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

Jove Lachman-Curl

Good info guys,
here is a good diagram from another ebay meter I came across. (nice URL link feature John will like that)
I think Cal should be able to use voltage as a good proxy for how much capacity he has left. He may want to throttle off, and measure pack voltage, that is one area where the steady voltage decline of lead acids is realy helpful vs lithium ion which don't seem to have much voltage sag over the central 90 of their capacity so voltage doesn't tell you much unless you're FUL or very empty. This should negate the need for a "reserve tank"... second image. C rate on the right side of the curve is full battery discharge per hour. so C=1 is discharged in one hour. C/3 =3hours. The article is an interesting read.

On Mon, Aug 31, 2020 at 6:02 PM johnacord <jcacord@...> wrote:
If you are running 80A, a 100A shunt is fine.  If you run a bit more than 100A it will just heat a little and that's OK for short periods.

I like to keep a shunt and meter around for testing and setting things up.  A meter made for panel mount is generally not so practical, generally needs voltage too, so I just use a shunt and my digital voltmeter.  The photo attached is a 50A 50mv shunt:  each mv read across the shunt is an amp.  I just wire it into whatever circuit I want to measure.

I don't know why 75mv shunts seem prevalent.  ?? Makes the reading an odd factor of amps, ie 75mv = 100A.  So how many amps is 32mv.........??

Remember, a shunt is just a precision resistor.  If you want to measure small currents just go buy a 1% resistor of the appropriate value from the electronic supply house and use the same way as in the photo.

John A

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

johnacord

If you are running 80A, a 100A shunt is fine.  If you run a bit more than 100A it will just heat a little and that's OK for short periods.

I like to keep a shunt and meter around for testing and setting things up.  A meter made for panel mount is generally not so practical, generally needs voltage too, so I just use a shunt and my digital voltmeter.  The photo attached is a 50A 50mv shunt:  each mv read across the shunt is an amp.  I just wire it into whatever circuit I want to measure.

I don't know why 75mv shunts seem prevalent.  ?? Makes the reading an odd factor of amps, ie 75mv = 100A.  So how many amps is 32mv.........??

Remember, a shunt is just a precision resistor.  If you want to measure small currents just go buy a 1% resistor of the appropriate value from the electronic supply house and use the same way as in the photo.

John A

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

Here's a quick sketch of where to hook up an ammeter shunt so it measures all the current coming in or going out of Cal's current setup, two battery banks, running one at a time. (see attachment)

On 8/31/2020 4:15 PM, I wrote:
Nice USB charger, worthless ammeter. <sigh> ALL the current flowing in and out of the batteries has to go through the ammeter, or it's shunt, to give any meaningful information. Cal's two 80 lb. thrust motors should draw in the neighborhood of 80 amps at full load. That little ammeter could go up in a puff of smoke if abused with that much current. <g>
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Re: Gauge Number from eBay ---- Wiring question, about 24 volt and "bridges" -- update for today

I talked to Cal a little while ago. He disconnected a possibly faulty cigar lighter socket and the 24-12 volt converter cooled right off. It's a good idea to have switch for the converter anyway.

On 8/31/2020 7:50 AM, Electri-Cal wrote:
...
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.
...
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Re: Gauge Number from eBay ---- Wiring question, about 24 volt and "bridges" -- update for today

There are some inexpensive battery monitors on Amazon. They're bound to be better than the little bitty one Cal just got. here's one:

https://smile.amazon.com/exec/obidos/ASIN/B01JOUZELG/themotherofal-20

The shunt isn't rated very much more than the maximum draw of Cal's motors, so a more robust one of the same mV rating might be needed:

https://smile.amazon.com/exec/obidos/ASIN/B07MNVZN7Z/themotherofal-20

Another possibility is to use a gauge that uses a Hall effect transformer to sense the current:

https://smile.amazon.com/exec/obidos/ASIN/B073W6453F/themotherofal-20

I'm not endorsing any of these products. Just showing some of what a quick look-see on Amazon turned up...

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Re: Mini 12 meter Boomer parts for 4 boats

Richard Green

It was a fun trip.  Two of us, 29 1/2 days to Astoria.  Sailing out and around the north pacific high we clocked about 3800 miles.  One day of gale winds but going our way, so to sing.  Stays’l only for the gale, hand steering hour on, hour off. Otherwise we self steered with surgical tubing to the tiller countering the stays’l sheet.
I cooked due to my food allergies.  Worked out great, didn’t have to do the dishes.  Heh.  That all was forty years ago right now.  1980.

Rich

On Aug 31, 2020, at 4:08 PM, Jove Lachman-Curl <jovelc87@...> wrote:

I bet that was quite an experience Rich, I'm jealous!
-Jove

On Mon, Aug 31, 2020 at 4:07 PM Richard Green <chaos5@...> wrote:
I sailed a FC version of Suhaili named Suhail, cutter rigged,  from Honolulu to Astoria in1980.  Fun trip, a bit bouncy.

Rich

On Aug 31, 2020, at 3:51 PM, Jove Lachman-Curl <jovelc87@...> wrote:

John,
As the fern ridge sailing season tapers off, I'm finding myself more and more interested in RC boats again.
Where can I catch people sailing RC boats around here?
How did the Boomer project go for everyone last year?
Are there any boomer hulls or other RC sailing equipment available?

Here is a nice picture of an RC model of Suhaili, Robin Knox-johston's 32'er. made by some French RC group.
At this point, I'd really like to try sailing and RC boat to just see if I like it before invest much more time or effort into the idea, So if anyone has a boat, knows a group, or etc. Let me know.
<image.png>
best,
-Jove

On Sun, Feb 24, 2019 at 4:50 PM Electri-Cal <calboats@...> wrote:
John, Dan, Andy and I have enough of the needed wires  coming in as a donation, to convert some servos, battery pack snaps, and enough RX battery cases to fit all 4 boats coming in soon.  I also have the keel to deck sealing tubes to be watertight.  Maybe more stuff will be added, but that is a complete list, until I actually get the work started.  I can order a bunch for all direct from source, so what I have is free, to those who don't mind waiting till it all comes in.  You guys can let me know if you want any of this, before it comes in.  John is covered, I will have the right stuff.  How about Dan, and  Andy,  are you interested or wish do do it yourself, no problem if you do??   A slight mod. needed to switch wires for fixing on the servos, and I ordered parts for that, or I might do those here as needed. So, let me know so I can start a "reserved boater packages" thing as goodies arrive, the rest I got, will restore a couple planes I have ready to convert.

Later,  Away we go , to the lonely sea and sky ,etc. ---   Cal                     RE, --  by John Masefield (Not me)  What a GREAT poem, tears, tears, -- etc.

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

Nice USB charger, worthless ammeter. <sigh> ALL the current flowing in and out of the batteries has to go through the ammeter, or it's shunt, to give any meaningful information. Cal's two 80 lb. thrust motors should draw in the neighborhood of 80 amps at full load. That little ammeter could go up in a puff of smoke if abused with that much current. <g>

A shorter link to the gauge:

https://preview.tinyurl.com/yxhon727

On 8/31/2020 8:18 AM, Jove wrote:
Here is the URL for the gurage, for anyone else looking.
https://www.ebay.com/itm/Dual-USB-Charger-LED-Digital-Display-Voltage-Amp-Meter-Voltmeter-Round-Car-Gauge/363000785546?hash=item5484886a8a:g:ipQAAOSwzEdeSFyE Cal,
to me it looks like it's designed that full amps would run through
that, but it is limited to 10A.
I bet there is a low ohm resistor in there calibrated with a voltage
gauge to display as current.
Not sure what your peak running amps is. You could bypass it with a
switch for sure, then just switch the ammeter in when you want to
check. That would prevent it having to tolerate all the current and
heat.
Heat is a function of amps in a device like this, so it's limit is
going to be heat dissipation and overheating, so if you only
switch it in when needed, it will survive a lot more. Perhaps it
will be willing to read higher amps, but if you put 20 amps through
it I bet it will blow after a few mins. It's all about cooling and
time. If the resistor is inside the plastic enclosure it will not
get much cooling, you could cut the back open if you wanted to cool
it more. even add a heat sink to that resistor.
If you're using up 4 of those full batteries in 8 hrs, that would be
one per 2hrs, ~500Wh/ hr. at 24v. =20 Amps, does that sound right?
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Re: Mini 12 meter Boomer parts for 4 boats

Jove Lachman-Curl

I bet that was quite an experience Rich, I'm jealous!
-Jove

On Mon, Aug 31, 2020 at 4:07 PM Richard Green <chaos5@...> wrote:
I sailed a FC version of Suhaili named Suhail, cutter rigged,  from Honolulu to Astoria in1980.  Fun trip, a bit bouncy.

Rich

On Aug 31, 2020, at 3:51 PM, Jove Lachman-Curl <jovelc87@...> wrote:

John,
As the fern ridge sailing season tapers off, I'm finding myself more and more interested in RC boats again.
Where can I catch people sailing RC boats around here?
How did the Boomer project go for everyone last year?
Are there any boomer hulls or other RC sailing equipment available?

Here is a nice picture of an RC model of Suhaili, Robin Knox-johston's 32'er. made by some French RC group.
At this point, I'd really like to try sailing and RC boat to just see if I like it before invest much more time or effort into the idea, So if anyone has a boat, knows a group, or etc. Let me know.
<image.png>
best,
-Jove

On Sun, Feb 24, 2019 at 4:50 PM Electri-Cal <calboats@...> wrote:
John, Dan, Andy and I have enough of the needed wires  coming in as a donation, to convert some servos, battery pack snaps, and enough RX battery cases to fit all 4 boats coming in soon.  I also have the keel to deck sealing tubes to be watertight.  Maybe more stuff will be added, but that is a complete list, until I actually get the work started.  I can order a bunch for all direct from source, so what I have is free, to those who don't mind waiting till it all comes in.  You guys can let me know if you want any of this, before it comes in.  John is covered, I will have the right stuff.  How about Dan, and  Andy,  are you interested or wish do do it yourself, no problem if you do??   A slight mod. needed to switch wires for fixing on the servos, and I ordered parts for that, or I might do those here as needed. So, let me know so I can start a "reserved boater packages" thing as goodies arrive, the rest I got, will restore a couple planes I have ready to convert.

Later,  Away we go , to the lonely sea and sky ,etc. ---   Cal                     RE, --  by John Masefield (Not me)  What a GREAT poem, tears, tears, -- etc.

Re: Mini 12 meter Boomer parts for 4 boats

Richard Green

I sailed a FC version of Suhaili named Suhail, cutter rigged,  from Honolulu to Astoria in1980.  Fun trip, a bit bouncy.

Rich

On Aug 31, 2020, at 3:51 PM, Jove Lachman-Curl <jovelc87@...> wrote:

John,
As the fern ridge sailing season tapers off, I'm finding myself more and more interested in RC boats again.
Where can I catch people sailing RC boats around here?
How did the Boomer project go for everyone last year?
Are there any boomer hulls or other RC sailing equipment available?

Here is a nice picture of an RC model of Suhaili, Robin Knox-johston's 32'er. made by some French RC group.
At this point, I'd really like to try sailing and RC boat to just see if I like it before invest much more time or effort into the idea, So if anyone has a boat, knows a group, or etc. Let me know.
<image.png>
best,
-Jove

On Sun, Feb 24, 2019 at 4:50 PM Electri-Cal <calboats@...> wrote:
John, Dan, Andy and I have enough of the needed wires  coming in as a donation, to convert some servos, battery pack snaps, and enough RX battery cases to fit all 4 boats coming in soon.  I also have the keel to deck sealing tubes to be watertight.  Maybe more stuff will be added, but that is a complete list, until I actually get the work started.  I can order a bunch for all direct from source, so what I have is free, to those who don't mind waiting till it all comes in.  You guys can let me know if you want any of this, before it comes in.  John is covered, I will have the right stuff.  How about Dan, and  Andy,  are you interested or wish do do it yourself, no problem if you do??   A slight mod. needed to switch wires for fixing on the servos, and I ordered parts for that, or I might do those here as needed. So, let me know so I can start a "reserved boater packages" thing as goodies arrive, the rest I got, will restore a couple planes I have ready to convert.

Later,  Away we go , to the lonely sea and sky ,etc. ---   Cal                     RE, --  by John Masefield (Not me)  What a GREAT poem, tears, tears, -- etc.

Re: Mini 12 meter Boomer parts for 4 boats

Jove Lachman-Curl

John,
As the fern ridge sailing season tapers off, I'm finding myself more and more interested in RC boats again.
Where can I catch people sailing RC boats around here?
How did the Boomer project go for everyone last year?
Are there any boomer hulls or other RC sailing equipment available?

Here is a nice picture of an RC model of Suhaili, Robin Knox-johston's 32'er. made by some French RC group.
At this point, I'd really like to try sailing and RC boat to just see if I like it before invest much more time or effort into the idea, So if anyone has a boat, knows a group, or etc. Let me know.

best,
-Jove

On Sun, Feb 24, 2019 at 4:50 PM Electri-Cal <calboats@...> wrote:
John, Dan, Andy and I have enough of the needed wires  coming in as a donation, to convert some servos, battery pack snaps, and enough RX battery cases to fit all 4 boats coming in soon.  I also have the keel to deck sealing tubes to be watertight.  Maybe more stuff will be added, but that is a complete list, until I actually get the work started.  I can order a bunch for all direct from source, so what I have is free, to those who don't mind waiting till it all comes in.  You guys can let me know if you want any of this, before it comes in.  John is covered, I will have the right stuff.  How about Dan, and  Andy,  are you interested or wish do do it yourself, no problem if you do??   A slight mod. needed to switch wires for fixing on the servos, and I ordered parts for that, or I might do those here as needed. So, let me know so I can start a "reserved boater packages" thing as goodies arrive, the rest I got, will restore a couple planes I have ready to convert.

Later,  Away we go , to the lonely sea and sky ,etc. ---   Cal                     RE, --  by John Masefield (Not me)  What a GREAT poem, tears, tears, -- etc.

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

Electri-Cal

Hi, Jove --- My motors are rated at 80 amps EACH full whup!!  That's a lot of drain, so I don"t do that.  If my gauge reads 10, that's a 20 amp draw.  Previous cruise was really 40 amps Up till the other day.   I was unaware of that high draw fact.  Now I plan on lowering the draw to say 15 amps, and see how I like the range.  "The range", "run time" etc. has to be longer, but every trip is depending on variables, what I need to get into is at what point do I turn back to the dock -- safely ??  New bigger batts will be a help when all is finished, and other options tried.

20 amps in 8 hours, that would be great, but I'm not there yet.  At full20 amps aver. per hr.  --- both banks as one, might make 4 hours plus a bit below battery good sense discharge rate.  Charlie called to say that we might get closer at 15 amps, both banks linked, --- ah, no reserve doing that.  However, just finished some wire-redo from gotta finish mode !!  I kept the old amp meter on when charging, before today.   The 24 to 12 volt reducer had then been left on whenever charging.  That  equipment drain was constant, an unwise procedure as it was the whole reduction setup always on, and staying hot to the touch.

I simply unplugged the ciggie light, and the whole system went cool, the new voltage light now lights up, and works fine.  No more extra leakage, the meter works, and four power transfer points are now rebuilt a bit better.  That's more like it, fixed that drain.  Charlie is bringing some gear to test stuff, then off to Dexter tomorrow.  Yet today I plan on a note card as to what I SHOULD do to preserve batteries.  I like to run at 4 to 5 mph, but not possible with two coots, so will be trying 3 to 4 max mph.  Not much difference, maybe I can learn to go that slow.  I plan on the new batteries to have a second pair in a month or two, then I can change the whole thing out. .

Meanwhile it works, a good deal !!  ----  Cal

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

Jove Lachman-Curl

Here is the URL for the gurage, for anyone else looking.

On Mon, Aug 31, 2020 at 8:17 AM Jove Lachman-Curl via groups.io <jovelc87=gmail.com@groups.io> wrote:
Cal,
to me it looks like it's designed that full amps would run through that, but it is limited to 10A.
I bet there is a low ohm resistor in there calibrated with a voltage gauge to display as current.
Not sure what your peak running amps is. You could bypass it with a switch for sure, then just switch the ammeter in when you want to check. That would prevent it having to tolerate all the current and heat.
Heat is a function of amps in a device like this, so it's limit is going to be heat dissipation and overheating, so if you only switch it in when needed, it will survive a lot more. Perhaps it will be willing to read higher amps, but if you put 20 amps through it I bet it will blow after a few mins. It's all about cooling and time. If the resistor is inside the plastic enclosure it will not get much cooling, you could cut the back open if you wanted to cool it more. even add a heat sink to that resistor.
If you're using up 4 of those full batteries in 8 hrs, that would be one per 2hrs, ~500Wh/ hr. at 24v. =20 Amps, does that sound right?

On Mon, Aug 31, 2020 at 7:50 AM Electri-Cal <calboats@...> wrote:
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: Gauge Number from eBay ---- Wiring question, about 24 volt and "bridges" -- update for today

Jove Lachman-Curl

Cal,
to me it looks like it's designed that full amps would run through that, but it is limited to 10A.
I bet there is a low ohm resistor in there calibrated with a voltage gauge to display as current.
Not sure what your peak running amps is. You could bypass it with a switch for sure, then just switch the ammeter in when you want to check. That would prevent it having to tolerate all the current and heat.
Heat is a function of amps in a device like this, so it's limit is going to be heat dissipation and overheating, so if you only switch it in when needed, it will survive a lot more. Perhaps it will be willing to read higher amps, but if you put 20 amps through it I bet it will blow after a few mins. It's all about cooling and time. If the resistor is inside the plastic enclosure it will not get much cooling, you could cut the back open if you wanted to cool it more. even add a heat sink to that resistor.
If you're using up 4 of those full batteries in 8 hrs, that would be one per 2hrs, ~500Wh/ hr. at 24v. =20 Amps, does that sound right?

On Mon, Aug 31, 2020 at 7:50 AM Electri-Cal <calboats@...> wrote:
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: 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

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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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,
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:
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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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.
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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

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