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Re: Gauge Number from eBay ---- Wiring question, about 24 volt and "bridges" -- update for today

Electri-Cal
 

The volt/amp guage is from  ------ cosupower888 ------  item #  363000785546

Yep, just the gauge, the box, no install notes, or anything beyond the info. on the eBay web site.  No mention of any bridge, hole size or uses.   I did look up other eBay identical gauges, some with more info.  I did just find that my inside boat long term battery charger also as a side effect made the instruments, and 12 volt converter for that quite warm, huh !!  I disconnected that and will check it today, maybe put a switch right close to it.  Looks like I need to isolate the charge current from going there, and find out why it would.  Even with all accessories shut off, that makes me wonder if there is an accidental drain going on that I don't know about.  Will look at that today, while I'm doing more boat stuff. 

I haven't turned on the instrument lights while running before.  I just used them as charge checkers, and the depth finder as a battery drain, since that buzzes, and shuts down.  I will figure the actual cut off points and use the LED instruments more now, probably make indicators for amp power for best range on the dial face.  A few things I didn't get to (forgot or lazy) while I was having  hip operations, and recovery months without boat oriented movements. 

Later coots,  ---- Cal



Later,   Cal  


Re: Wiring question, about 24 volt and "bridges"

 

John A informed me that the BMV-700 is a bit cheaper, but will do all most of us need:

https://www.victronenergy.com/battery-monitors/bmv-700

https://www.victronenergy.com/upload/documents/Datasheet-BMV-700-series-EN.pdf

Thanks, John!

On 8/30/2020 8:38 PM, I wrote:
...
Maybe someday Tuffy will get a Victron BMV-702 as a present. <g>
https://www.victronenergy.com/battery-monitors/bmv-702
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I am patient with stupidity but not with those who are proud of it. (Edith Sitwell)
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Re: Batteries again, Upgrade

 

My spreadsheet probably _could_ use some adjusting. ;o) I've attached it, in crude form, if anyone is interested. I could probably find a Peukert effect calculating spreadsheet somewhere on the Interweb, but then how would I learn anything? <g> The top part is if you know the 20 hour A/H rate for a battery, the lower part uses the 25 amp discharge time.

I based my calculations on the 25 amp rating Interstate gives -- 160 minutes. I get about 66 3/4 A/H at that rate. My calculations end up with a plausible run time for Cal's combined battery pack,near what 6 mid-range Interstate golf cart batteries in series would have.

I don't understand the "At a discharge of 25A ==> 56A effective (25 raised to the 1.25 power)" My math is rusty, but I don't see how that agrees with the Peukert Law formulae given on the Wikipedia page...

https://en.wikipedia.org/wiki/Peukert%27s_law

On 8/29/2020 7:58 PM, John A wrote:
John,
Perhaps your spreadsheet needs a bit of adjustment.
Interstate does not give an AH rating for that battery, but in general one might expect a good group 27 to be 100AH (20 Hr rate).  A Peukert constant of 1.25 should not be far off, maybe a bit low but probably not as much as 1.4.  Using my calculator I get the following for peukert 1.25:
At a discharge of 25A ==> 56A effective (25 raised to the 1.25 power), 107 min to full discharge.
At a discharge of 12.5A ==> 23.5A effective, 255 min to full discharge.
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Re: Wiring question, about 24 volt and "bridges"

 

I've got a Link 10 in Tuffy. I wish I'd done more research before I bought it. <sigh> It's designed for an installation where it's permanently (or nearly) hooked up to the batteries, and the batteries are charged in situ. I first hooked up the gauge on the downstream side of the battery switch, but when the switch was turned on the power introduction to the gauge was too "ragged" (Link 10's term) and more often than not the gauge display would freeze up. Now I've got the Link 10 hooked up directly to the battery bank, and the gauge only occasionally freezes up when it awakes. I pull the fuses to the gauge when I take the batteries out to charge them, and carefully reinsert them in the right order after the batteries are reinstalled. Sometimes it even works right on the first try! <g>

Maybe someday Tuffy will get a Victron BMV-702 as a present. <g>

https://www.victronenergy.com/battery-monitors/bmv-702

On 8/30/2020 11:22 AM, John A wrote:
Good comments Myles.  I have read many comments about the problems with Link and other similar.
I have used the Victron BMV-702 for 5 years or so without any problems, good readings and accuracy.  The power connection is on the shunt and connected directly to the battery through a fuse.  So power up is simultaneous with battery connection.  Installation sheet attached showing the arrangement graphically.
I did modify the arrangement in my installation so that the power to the BMV readout from the battery was after the main battery switch.  The BMV does draw a little current so doing this reduces a small battery drain when the boat is parked.
--
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Re: Wiring question, about 24 volt and "bridges"

 

It sounds like you just got the gauge itself. Cal. You need a properly rated shunt to hook it up. The gauge needs a particular mV rating, and needs to be rated well above the amperage you expect to draw. The instructions for the gauge should say something like, "use with a 50 mV shunt", or whatever. Unfortunately, the mV rating doesn't seem to be standardized... You mentioned that you've got a bunch of shunts lying around; if you're lucky maybe you've got one to match the gauge. Use one shunt per ammeter. Don't just hook the digital gauge to the shunt you use with your dial gauge, even if it's the proper mV rating.

Hook the shunt up into the common ground going into your battery bank(s) so the gauge reads all the current going out, or in, to the batteries. It should be easy enough to hook you temporary backup pack through the common ground.

If that gauge is indeed a Link 10 knockoff, it'll run on 24 volts with no problem.

On 8/30/2020 8:39 AM, Electri-Cal wrote:
Probably Myles Tweete has this, but others may wonder about this.  I just got in a new round gauge for Surprise. A dual amp and volt type, that should show all I need in a small package.  The info shows it will handle decent numbers of current, and also shows on several web sites where it is hooked up.  I'm not fond of running the full 24 volts through the wires, even though the draw is miniscule.  There has got to be more to thisthan i'm seeing ??
...
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Re: Batteries again, Upgrade

 

I'll bet that 88 A/H is at the 5 hr. rate, not the usual, 20 hr. rate. 88 A/H would be pretty feeble for a group 27 deep cycle, but about right at the 5 hr. rate. I think I've seen a group 27 so rated somewhere... The attached Trojan chart might be useful, to see how a battery manufacturer can easily give you more useful info.

On 8/30/2020 8:04 AM, John A wrote:
....dig deep (sigh) enough and you can find the info!  The Interstate Group 27 is rated at 88AH.  So the run times a bit less, 96min/225min.
Using AGM instead of flooded cell will give you more.  My Lifeline battery has a peukert of 1.12,
so at 25A ==> 37A effective, and at 12.5A ==> 17A effective, for 1.5x run time.
--
John <@Jkohnen>
The right to be heard does not automatically include the right to be taken seriously. (Hubert Humphrey)
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Re: Wiring question, about 24 volt and "bridges"

Electri-Cal
 

I just spent today mainly staring at wiring I did maybe 4 years ago.  Not much fun, but I did get some stuff redone, other stuff is maybe for later.  The results matter, but all works better if not perfect, but works.   

The first voltage gauge was partially shot, as it s led numbers showed low voltage and about  half a lighted green, yellow red outer statuss ring about  half working also.  I changed for the new similar gauge, voila -- there was the same voltage as my meter said.  Then I plugged in a voltahe lighted meter into my ciggie lighter, the voltage was within .01 of  the other meter, so thats a help.  Then after fooling around I found a different unused plug, which had 24 volts, so I could use that as the amps plug, big maybe !!   I can now read the pack voltage two ways, and when it drops to where to depth finder dies, switch packs, reading that voltage figure as safe.   

Shunts I got !!  Each set of cables connect to shunts, with recommended fuses for power maximums, trickle chge., 12v. accessories consoles, and etc.  Up to the  point where I have no more bolt space for new connections.  any more adding stuff and it would take custom fuse, acc. link holders.  Don't think I'd like to go there.   I don't think it will be fun to add another plug  system for the third pack.  Almost easier to think I can plug in the genset to the standard charge plug, and less weight too, yeah some noise !!  Think i'll call local Honda shop for the slightly odd size fuses required, shorter  length.

Now I'll reread all your good  previous notes, and see what to change or think about next, ---  a bit  hot to do much more right now,  Thanks coots, ---  Cal

 


Re: Wiring question, about 24 volt and "bridges"

johnacord
 

Good comments Myles.  I have read many comments about the problems with Link and other similar.

I have used the Victron BMV-702 for 5 years or so without any problems, good readings and accuracy.  The power connection is on the shunt and connected directly to the battery through a fuse.  So power up is simultaneous with battery connection.  Installation sheet attached showing the arrangement graphically.

I did modify the arrangement in my installation so that the power to the BMV readout from the battery was after the main battery switch.  The BMV does draw a little current so doing this reduces a small battery drain when the boat is parked.

John A


Re: Wiring question, about 24 volt and "bridges"

Myles Twete
 

Ditto.

If this round gauge is a descendant of the Link-10, which was a descendant of the E-Meter (designed/built in Arlington, Wa.), there’s definitely a need for an external shunt.  Worse, to the extent that these new round multi-function gauges (Amps/Volts/Amp-Hours, etc.) are knock-offs without a redesign, beware that both the E-Meter and Link-10 meters have a design flaw whereby the current monitoring (and A-H) features die a quick death if power is not applied in the right sequence to the inputs.  I didn’t want to risk it, so I did what others did and mounted a connector at the back end so that all the connections could be connected simultaneously, which works.  Still, I ultimately bricked at least one of these…

So hopefully these new Amphour gauges out there have been made more robust.

 

-MT

 

From: oregoncoots@groups.io [mailto:oregoncoots@groups.io] On Behalf Of Jove Lachman-Curl
Sent: Sunday, August 30, 2020 9:47 AM
To: oregoncoots@groups.io
Subject: Re: [oregoncoots] Wiring question, about 24 volt and "bridges"

 

Hey Cal,

Can you see us images and a website where we can look up the Guage in question other wise this is really hard to give input on.

I can say that current is usually measured via voltage drop across a calibrated low resistance resistor (typically called a shunt). That might be integral to your unit, and if so there would be fairly large terminals on your Guage to match the current.

You will not have much success running full amps through thin instrument wires but im sure you know that.

 

On Sun, Aug 30, 2020, 8:39 AM Electri-Cal <calboats@...> wrote:

Probably Myles Tweete has this, but others may wonder about this.  I just got in a new round gauge for Surprise. A dual amp and volt type, that should show all I need in a small package.  The info shows it will handle decent numbers of current, and also shows on several web sites where it is hooked up.  I'm not fond of running the full 24 volts through the wires, even though the draw is miniscule.  There has got to be more to thisthan i'm seeing ??

All my other gauges hook through the twin bus bars, with drop screws on each end so full power drops 24 volt to 12 volt.  I have fused blocks for these 12 v, accessories, lights, radio etc.  This new guage does not show that bus bar anyplace in the on line circuit, several I liiked at do not show any bus bar>>.  How does that work??  Do I just run light instrument wires at full power??  Is there another voltage drop bar, that  is assumed to be there??  Do I just connect to the pack 24 v. and it is handled inside the guage??  Hook to the regular 12v. take off, and the variable senses what is required??  maybe my confusion is because I haven't  done a mini//multi guage like this I recall.    Or last, just touch the terminals and hope the guage hangs together.

My normal inclination is to just visually double tha amp draw, but it was suggested I need to have the right numbers on the guage.   I figured colored tape at correct cruise speeds was good enough, but I bought tha guage since it is a lighted colored digital one.

Anybody with the right info on this ??  Thanks,  Cal



   


Re: Wiring question, about 24 volt and "bridges"

Jove Lachman-Curl
 

Hey Cal,
Can you see us images and a website where we can look up the Guage in question other wise this is really hard to give input on.
I can say that current is usually measured via voltage drop across a calibrated low resistance resistor (typically called a shunt). That might be integral to your unit, and if so there would be fairly large terminals on your Guage to match the current.
You will not have much success running full amps through thin instrument wires but im sure you know that.

On Sun, Aug 30, 2020, 8:39 AM Electri-Cal <calboats@...> wrote:
Probably Myles Tweete has this, but others may wonder about this.  I just got in a new round gauge for Surprise. A dual amp and volt type, that should show all I need in a small package.  The info shows it will handle decent numbers of current, and also shows on several web sites where it is hooked up.  I'm not fond of running the full 24 volts through the wires, even though the draw is miniscule.  There has got to be more to thisthan i'm seeing ??

All my other gauges hook through the twin bus bars, with drop screws on each end so full power drops 24 volt to 12 volt.  I have fused blocks for these 12 v, accessories, lights, radio etc.  This new guage does not show that bus bar anyplace in the on line circuit, several I liiked at do not show any bus bar>>.  How does that work??  Do I just run light instrument wires at full power??  Is there another voltage drop bar, that  is assumed to be there??  Do I just connect to the pack 24 v. and it is handled inside the guage??  Hook to the regular 12v. take off, and the variable senses what is required??  maybe my confusion is because I haven't  done a mini//multi guage like this I recall.    Or last, just touch the terminals and hope the guage hangs together.

My normal inclination is to just visually double tha amp draw, but it was suggested I need to have the right numbers on the guage.   I figured colored tape at correct cruise speeds was good enough, but I bought tha guage since it is a lighted colored digital one.

Anybody with the right info on this ??  Thanks,  Cal



   


Wiring question, about 24 volt and "bridges"

Electri-Cal
 

Probably Myles Tweete has this, but others may wonder about this.  I just got in a new round gauge for Surprise. A dual amp and volt type, that should show all I need in a small package.  The info shows it will handle decent numbers of current, and also shows on several web sites where it is hooked up.  I'm not fond of running the full 24 volts through the wires, even though the draw is miniscule.  There has got to be more to thisthan i'm seeing ??

All my other gauges hook through the twin bus bars, with drop screws on each end so full power drops 24 volt to 12 volt.  I have fused blocks for these 12 v, accessories, lights, radio etc.  This new guage does not show that bus bar anyplace in the on line circuit, several I liiked at do not show any bus bar>>.  How does that work??  Do I just run light instrument wires at full power??  Is there another voltage drop bar, that  is assumed to be there??  Do I just connect to the pack 24 v. and it is handled inside the guage??  Hook to the regular 12v. take off, and the variable senses what is required??  maybe my confusion is because I haven't  done a mini//multi guage like this I recall.    Or last, just touch the terminals and hope the guage hangs together.

My normal inclination is to just visually double tha amp draw, but it was suggested I need to have the right numbers on the guage.   I figured colored tape at correct cruise speeds was good enough, but I bought tha guage since it is a lighted colored digital one.

Anybody with the right info on this ??  Thanks,  Cal



   


Re: Batteries again, Upgrade

johnacord
 

....dig deep (sigh) enough and you can find the info!  The Interstate Group 27 is rated at 88AH.  So the run times a bit less, 96min/225min.

Using AGM instead of flooded cell will give you more.  My Lifeline battery has a peukert of 1.12,
so at 25A ==> 37A effective, and at 12.5A ==> 17A effective, for 1.5x run time.

John A


Re: September Columbia Cruise

Mark Neuhaus
 

I stopped by Fred's Marina yesterday to ask about fishing crowds and slips for the week of the cruise.  A fisherman said that fall salmon season on the Columbia was something like three days this weekend and one or two later this week. So it should be no problem launching and parking at Fred's.  The harbor master seemed to think slips would be no problem at that time either. I saw plenty of spaces open.

The fee for launching is ten bucks.  Ends up, if you leave your rig there, that's ten bucks a day. I asked about any discounts and he said he might be able to do a group discount if someone wanted to call or email him. Sorry, I forgot to ask slip fees.

So, attached should be his card and if someone who will be using their facilities is interested, you can contact him and work things out.

Hope this helps.

Mark


Re: Batteries again, Upgrade

johnacord
 

John,

Perhaps your spreadsheet needs a bit of adjustment. 

Interstate does not give an AH rating for that battery, but in general one might expect a good group 27 to be 100AH (20 Hr rate).  A Peukert constant of 1.25 should not be far off, maybe a bit low but probably not as much as 1.4.  Using my calculator I get the following for peukert 1.25:

At a discharge of 25A ==> 56A effective (25 raised to the 1.25 power), 107 min to full discharge.

At a discharge of 12.5A ==> 23.5A effective, 255 min to full discharge.

John A


Re: Batteries again, Upgrade

 

I did a little fooling around in a spreadsheet with Peukert's Law. If I calculated correctly, using the 25 amp rating of Interstate group 27 deep cycle batteries, and a, probably optimistic, Peukert constant of 1.25:

Cal's two battery packs of two group 27s are each rated at 160 minutes at a 25 amp discharge. 320 minutes total for the packs used separately.

If he hooked the packs together in parallel the current draw per battery would be cut in half, 12.5 amps. My calculations show that at that discharge rate the combined pack would go about 381 minutes. Almost 19% longer, and similar to four mid-range Interstate golf cart batteries hooked up in series.

Using a pessimistic Peukert constant of 1.4 the run time with the combined pack at 12.5 amps would be about 423 minutes.

Halve the minutes above for the real world, where you want to use the batteries more than once. <g>

The truth of Cal's batteries' Peukert constant lies somewhere in between these extremes, and I may be way off base with my calculations... <g>

https://en.wikipedia.org/wiki/Peukert%27s_law

--
John <@Jkohnen>
Wind is to us what money is to life on shore. (Sterling Hayden)


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Re: Batteries again, Upgrade

 

Thanks, Myles! I think I now understand why parallel connections are riskier than serial ones. Sounds like fuses between batteries, or battery banks, hooked up in parallel are a Good Idea. Cheaper than current limiting isolators? IIR Susanne and Phil's article on Lily (I gave a bunch of old MAIBs to John McC, who was gonna cut out the Bolger articles and/or scan them, I'm hoping he's got a copy of that one) they said there was some power loss through the isolators. More than through fuses? I suspect that a fuse sized to blow at a current well above the maximum draw from the motor wouldn't have much resistance at normal operating currents...

Dennis B, who's soon gonna have a motorboat named after him <g>, had a catastrophic failure of one of the six golf cart batteries hooked up in series in his tug, Lady-J. That one battery got hot enough to melt the top of the case, but the other batteries survived the ordeal and served for a few more years.

I really appreciate you sharing your actual experience with electric boating with us, Myles.

On 8/28/2020 7:25 PM, Myles T wrote:
I’ve had a lot of experience paralleling batteries on an electric boat---arguably as much or more than anyone else.
...
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John <@Jkohnen>
For will anyone dare to tell me that business is more entertaining than fooling among boats? He must have never seen a boat or never seen an office, who says so. (Robert Louis Stevenson)
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Re: Batteries again, Upgrade

Electri-Cal
 

Wow!  Tons of great input on this.  The interstate M series seem to be a slight improvement over 27 standard builds.  Too bad I can't just plug a pair into the other battery pack, due to different capacities, and age, not much but not the same.  Looking at adding another input plug for #3 battery pack with a on/off switch.  That way I can isolate the original 4 battery pack.  Makes for a 4 bat. pack to cruise, with a two battery new pack behind the seat for reserve, turn off main, flip switch on for secondary, easy to do, and satisfies my desire for that backup reserve.  Maybe get this extra plug in Monday or so, but there are some connector issues, like running out of connector bolt threaded length, always something!!

The gen set plugged with my110v. variable charger could -- as a different option to the third pack, not together -- then can use the original charge input, just like on land.  Again, to extend range, probably not enough to replace the total draw amps. That is to be tested as option Two, with a different result.  Weight is like one battery, output to be tested on land next week.  Charlie and I for Tuesday, John K. on Wed.  I need to find a "close by" better lake than Dexter, that has water!!

Surprise can only handle just so much weight, so unless I add mega$$$, that will always be an issue, Later Coots --- Still Reading all This ---   Cal. 


Re: Batteries again, Upgrade

Richard Green
 

Huh?  Wha..?

Rich

On Aug 28, 2020, at 7:25 PM, Myles Twete <matwete@...> wrote:

I’ve had a lot of experience paralleling batteries on an electric boat---arguably as much or more than anyone else.
I converted the outboard on The Reach Of Tide to electric in 2003.  Initially, it was powered by a 60# ADC series-wound motor and a series string of 6 - 6volt Trojan 220ah batteries.  When I opted to double the capacity by adding another string of Trojans, I briefly considered paralleling batteries at the battery level, but ultimately decided to parallel at the string voltage instead.  In the extremely rare case of shorting a cell, a paralleled battery pair (6v) definitely could see a lot of current flowing one to the other given perhaps a 30% voltage stress (2v/6v) with a shorted cell.  Paralleling at the string level though, a single cell short in one of the batteries in a string would only stress about 5% (2v/36v), so wouldn’t expect a lot of current.  I ran with this arrangement and without even fusing between the strings for many years.  I NEVER ran with one string, then switched to the other---always I considered Peukert loss as more important and always kept the strings paralleled, whether at rest, cruising or charging.  I never had any issues.  This pack was rated 36v & 450ah or so (20hr rate).
 
Since 2014 or so, I’ve been running with lithium (nom.42v & 700ah).  Effectively, I have q:20 42v lithium batteries all connected up in parallel.  I do have a nom. 10amp (or is it 20?) fuse at each of these.  Each of these batteries is actually a stack of 12 pairs of lithium cells---i.e. 240 lithium cells are paralleled up with a partner.  If I happened to have a shorted cell (or more likely, a leaky cell), the immediate effect is to stress the adjacent cell.  Nothing new there, as this is the same risk when used in cars.  Typically either a leaky cell or a leaky BMS transistor causes this and I’ve had about 6 cell pairs in my pack that have been impacted.  With 12 pairs in the internal series string, and paralleling at the string level, a leaky cell or BMS channel results in that cell voltage dropping (and so also the string voltage).  But with 19 other strings in parallel, the string voltage is maintained.  The result?  In the bad string, 11 cell pairs see their voltage increase while the leaky pair continues to collapse.  It’s important to not let that situation continue, so at least occasional monitoring of cell voltages is important---I check the cell voltages in the pack about once a year, or about once every 5 charge cycles.  I do not trust the BMS to be connected and powered continuously---they do draw power (about 1watt each) and MOSFET bypass transistors can fail shorted or leak, so I only power them when I need to.
 
Even with just 1 of these lithium strings, the Peukert effect is minimal with my setup.  With 20x strings in parallel, I could use my pack as an arc-welder power source and it wouldn’t flinch.  And so, it’s important to put current protection in the right places.  My motor draws up to 200amps continuous at up to 48v with the pack as it’s configured.  Each of those strings only sees about 10amps, or about 0.3C current draw.  And for a typical cruise (maybe 50-80amps continuous), the cells only see about 0.1C.  So this pack is very minimally stressed compared to the perhaps 1C discharge and regen rates seen with these batteries in an EV.  This pack might outlive the boat. J
 
Anyway, I don’t use diodes, but I love fuses and I don’t have a problem with paralleling batteries at the right levels for the right reasons.
 
Your mileage may vary-
 
-Myles T.
 
 
 
From: oregoncoots@groups.io [mailto:oregoncoots@groups.io] On Behalf Of Randy Torgerson
Sent: Friday, August 28, 2020 4:26 PM
To: oregoncoots@groups.io
Subject: Re: [oregoncoots] Batteries again, Upgrade
 
John,
 

Yes, "runaway current from a strong battery to a weak one" is a real concern.  If one battery shorts a cell then the stronger battery will try to equalize the voltage with a large current resulting.  The large current can melt the interconnecting cables, the terminal and sometimes cause a battery to expand or explode.  Isolating the batteries when charging will lessen the risk.  Also if you are going to parallel batteries make sure they are the same type, manufacturer and date code.  This only only lessens the risk.  Fuse between the batteries can be a life saver.  An ACR (Automatic charge Relay) are now used to change two batteries from the same charge source.  The first  battery is charged and when the voltage reaches a setpoint then the second battery is charged also.  If the second battery's voltage is too low the ACR disconnects and the cycle repeats slowly.

Randy 



Re: Batteries again, Upgrade

Myles Twete
 

I’ve had a lot of experience paralleling batteries on an electric boat---arguably as much or more than anyone else.

I converted the outboard on The Reach Of Tide to electric in 2003.  Initially, it was powered by a 60# ADC series-wound motor and a series string of 6 - 6volt Trojan 220ah batteries.  When I opted to double the capacity by adding another string of Trojans, I briefly considered paralleling batteries at the battery level, but ultimately decided to parallel at the string voltage instead.  In the extremely rare case of shorting a cell, a paralleled battery pair (6v) definitely could see a lot of current flowing one to the other given perhaps a 30% voltage stress (2v/6v) with a shorted cell.  Paralleling at the string level though, a single cell short in one of the batteries in a string would only stress about 5% (2v/36v), so wouldn’t expect a lot of current.  I ran with this arrangement and without even fusing between the strings for many years.  I NEVER ran with one string, then switched to the other---always I considered Peukert loss as more important and always kept the strings paralleled, whether at rest, cruising or charging.  I never had any issues.  This pack was rated 36v & 450ah or so (20hr rate).

 

Since 2014 or so, I’ve been running with lithium (nom.42v & 700ah).  Effectively, I have q:20 42v lithium batteries all connected up in parallel.  I do have a nom. 10amp (or is it 20?) fuse at each of these.  Each of these batteries is actually a stack of 12 pairs of lithium cells---i.e. 240 lithium cells are paralleled up with a partner.  If I happened to have a shorted cell (or more likely, a leaky cell), the immediate effect is to stress the adjacent cell.  Nothing new there, as this is the same risk when used in cars.  Typically either a leaky cell or a leaky BMS transistor causes this and I’ve had about 6 cell pairs in my pack that have been impacted.  With 12 pairs in the internal series string, and paralleling at the string level, a leaky cell or BMS channel results in that cell voltage dropping (and so also the string voltage).  But with 19 other strings in parallel, the string voltage is maintained.  The result?  In the bad string, 11 cell pairs see their voltage increase while the leaky pair continues to collapse.  It’s important to not let that situation continue, so at least occasional monitoring of cell voltages is important---I check the cell voltages in the pack about once a year, or about once every 5 charge cycles.  I do not trust the BMS to be connected and powered continuously---they do draw power (about 1watt each) and MOSFET bypass transistors can fail shorted or leak, so I only power them when I need to.

 

Even with just 1 of these lithium strings, the Peukert effect is minimal with my setup.  With 20x strings in parallel, I could use my pack as an arc-welder power source and it wouldn’t flinch.  And so, it’s important to put current protection in the right places.  My motor draws up to 200amps continuous at up to 48v with the pack as it’s configured.  Each of those strings only sees about 10amps, or about 0.3C current draw.  And for a typical cruise (maybe 50-80amps continuous), the cells only see about 0.1C.  So this pack is very minimally stressed compared to the perhaps 1C discharge and regen rates seen with these batteries in an EV.  This pack might outlive the boat. J

 

Anyway, I don’t use diodes, but I love fuses and I don’t have a problem with paralleling batteries at the right levels for the right reasons.

 

Your mileage may vary-

 

-Myles T.

 

 

 

From: oregoncoots@groups.io [mailto:oregoncoots@groups.io] On Behalf Of Randy Torgerson
Sent: Friday, August 28, 2020 4:26 PM
To: oregoncoots@groups.io
Subject: Re: [oregoncoots] Batteries again, Upgrade

 

John,

 

Yes, "runaway current from a strong battery to a weak one" is a real concern.  If one battery shorts a cell then the stronger battery will try to equalize the voltage with a large current resulting.  The large current can melt the interconnecting cables, the terminal and sometimes cause a battery to expand or explode.  Isolating the batteries when charging will lessen the risk.  Also if you are going to parallel batteries make sure they are the same type, manufacturer and date code.  This only only lessens the risk.  Fuse between the batteries can be a life saver.  An ACR (Automatic charge Relay) are now used to change two batteries from the same charge source.  The first  battery is charged and when the voltage reaches a setpoint then the second battery is charged also.  If the second battery's voltage is too low the ACR disconnects and the cycle repeats slowly.

Randy


Re: Batteries again, Upgrade

Randy Torgerson
 

John,


Yes, "runaway current from a strong battery to a weak one" is a real concern.  If one battery shorts a cell then the stronger battery will try to equalize the voltage with a large current resulting.  The large current can melt the interconnecting cables, the terminal and sometimes cause a battery to expand or explode.  Isolating the batteries when charging will lessen the risk.  Also if you are going to parallel batteries make sure they are the same type, manufacturer and date code.  This only only lessens the risk.  Fuse between the batteries can be a life saver.  An ACR (Automatic charge Relay) are now used to change two batteries from the same charge source.  The first  battery is charged and when the voltage reaches a setpoint then the second battery is charged also.  If the second battery's voltage is too low the ACR disconnects and the cycle repeats slowly.


Randy