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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  


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  


Jove Lachman-Curl
 


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  


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 


 

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?
--
John <@Jkohnen>
I have noticed that people who are late are often so much jollier than the people who have to wait for them. (Edward Verrall Lucas)
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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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John <@Jkohnen>
Missionaries, my Dear! Don't you realize that missionaries are the divinely provided food for destitute cannibals? Whenever they are on the brink of starvation, Heaven in its infinite mercy sends them a nice plump missionary. (Oscar Wilde)


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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.
...
--
John <@Jkohnen>
I want people to talk to one another no matter what their difference of opinion might be. (Studs Terkel)
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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>
--
John <@Jkohnen>
The security of the Kingdom is increased by every man being more or less a sailor. (Capt. Marryat)
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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


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.
image.png
image.png

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


 

That's good to know. Thanks, John. That means for about 16 bucks Cal could get a battery monitor that seems to work alright, from the reviews, and wouldn't have to buy anything extra:

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

I keep learning... I thought that the voltage drop rating -- mV -- was for a set current determined by some standard. Say 100 amps, so a 75 mV shunt would have a voltage drop of 75 mV at 100 amp current, whether the shunt was rated to handle 100 amps or 500 amps. No. That'd make life too easy. <g> If your gauge says to use a 75 mV, 100 amp shunt, then you'd better use a shunt just like that:

"Shunts are rated by the maximum current and voltage drop at that current. For example, a 500 A, 75 mV shunt would have a resistance of 150 microohm, a maximum allowable current of 500 amps and at that current the voltage drop would be 75 millivolts. By convention, most shunts are designed to drop 50 mV, 75 mV or 100 mV when operating at their full rated current and most ammeters consist of a shunt and a voltmeter with full-scale deflections of 50, 75, or 100 mV. All shunts have a derating factor for continuous (more than 2 minutes) use, 66% being the most common, so the example shunt should not be operated above 330 A (and 50 mV drop) longer than that."

https://en.wikipedia.org/wiki/Shunt_(electrical)

I'm gonna visit Cal Wednesday to see what's going on with Surprise's wiring.

On 8/31/2020 6:02 PM, john acord 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.
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John <@Jkohnen>
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johnacord
 

Jove,

That's an interesting graph of state of charge, SOC, vs discharge rate, and appears to be at a constant load (with various load rates graphed).  How does that relate to varying loads?

SOC of a lead acid by voltage reading is normally determined at rest, and for an accurate SOC at rest for 12-24 hours.  When the load goes to zero, or some small %, then the battery will rise to a voltage less than true reading of SOC.  This can be a good representation of SOC with a somewhat small bias short of real SOC as long as you take the reading in the same way consistently.

Before I had an Amp-Hour meter I just had two readouts, voltage and current.  By reading the voltage a time after the current dropped to the minimum value (assuming there were always some small loads) I would get a good idea of the SOC.  It seemed to be within a few percent, but the main thing was to see that I did not discharge too deeply.

John A


Electri-Cal
 

Hey, Jove, had a cheap to do idea for an easy voltage check.  The cigarette plug got a lighted double USB plug that also shows the voltage from my 12 volt reducer for lights, smokes, or whatever.  So, I just plug it in fully, and there is the voltage, for a 12 volt single batt.  Just double that and thee is the 24 volt status, or use the single figure to see when to turn back home.  A common sense idea, that backs up my depth finder going dark at 11.5 volts -- or a low battery pack overall.

Catch you Later, ---  Cal


Electri-Cal
 

Didn't replace the higher limit amp meter, still the 150 amp reading for now.   I'm just replacing the fuse for accessories, and using the ciggie lighter with amp gauge.  Mentally double the draw, and that is the true figure, again -- for now.  With new battery hook up, I can blow accessory fuses if I push it too fast, couldn't do that before -- hah.

I'm installing a new 10kv genset in a sound resistant box, with home hookup stuff, that is enough project till I get the new gauge in from China to put in.  meanwhile, time to get wet this fall !!!

Later, Coots ----  Cal


 

Didn't you install the ammeter shunt in the common ground, like we had it for the separate two-battery banks? That'd give the true current draw.

I'm glad the serial/parallel single bank worked out as expected.:o)

On 10/2/2020 10:55 AM, Electri-Cal wrote:
Didn't replace the higher limit amp meter, still the 150 amp reading for now.   I'm just replacing the fuse for accessories, and using the ciggie lighter with amp gauge.  Mentally double the draw, and that is the true figure, again -- for now.  With new battery hook up, I can blow accessory fuses if I push it too fast, couldn't do that before -- hah.
I'm installing a new 10kv genset in a sound resistant box, with home hookup stuff, that is enough project till I get the new gauge in from China to put in.  meanwhile, time to get wet this fall !!!
--
John <@Jkohnen>
If liberty means anything at all, it means the right to tell people what they do not want to hear. (Eric Blair)
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