? Interpreting an ammeter... ?

[TimC]

The nice thing is I'm camping and if I run out of power it isn't the end of the world. ...I'll still be able to function without the phone.

MADNESS!!!

Tom

Haa haa. Many places I roam a dead battery is not the problem. Cell signal is another issue entirely. Like many of us i am on my phone more than I care to admit. I do manage to function without it though.

[saltydawg]

Okay my real answer

I like the ali 41 buck meter from amazon, it gives a % of charge used/remaining etc

[TimC]

After you use a few times and monitor it you can get a feel for what its got left. There are charts like this one in the morning before the solar starts charging see what the voltage is and compare to the chart. For example if it says you used about 30% because voltage is 12.3 ish, then the watts you used would be about 30% of capacity. In my case, my 85AH battery is acting more like 100AH.
Tom

Tim

So I am revisiting this thread as I am experiencing some battery bank problems. Seems the state of charge is dropping way off but I'm not sure I am testing enough times to make a determination. Maybe Tom will chime in again and let me know what else I could test. This was an AGM 144 aHr bank when new.

I charged the battery fully with a NOCO 7200. Disconnected the charger and my solar is not producing any watts being in a garage. Here are the ammeter numbers. Ignore the lower meter, that is production. The top image is the load.

At full charge before any load


I then turned on everything, fridge, lights, radio, fans, and even a 12v blanket. After three hours and at about 10.53v the fridge low voltage setting turned it off. The blanket had shut off on its own 45 minute timer. The 10.53v is worrisome and I don't understand if that is a normal reading or reflects a very weak battery.



By learnmetrics.com's calculations the 143wh is about 11.92 aHr. After an 18 minute rest with no load the battery is up to 12.43v. I know it should probably rest for hours to be more accurate. I'll read it again in the morning after a good 12 hour rest.



So, if I'm understanding Tom's explanation that a 12.43v value shows I have used 20% of my battery capacity. If the battery could actually provide another 210wh that would mean it gave up 50% or 350wh (29.7 aHr). That's assuming a straight line depletion and I'm doubting that it will give another 30% since it showed already at 10.53v.

Are my calculations faulty, or my method faulty or is my bank really in poor condition? Should I do this test several times and average the results? This is a six year old bank and I accept that it may be ready for the recycle bin. I am just trying to figure out what the end of battery life looks like.

Thanks, Tim

[Socal Tom]

So there are one or two things going on.

1) You can't really trust the voltage measurement when you have a big amp draw, the blanket and the fridge pull big numbers, so its going to give an artificially low number, additionally deep cycle batteries don't like rapid discharging. The are designed for a long slow drain. ( but a bigger wire between the battery and the fridge might help with that, but ultimately that electric blanket is probably creating a big draw and the battery can't keep up with both.

The way I do the math, 143 wh are 20% of the battery capacity, so total would be 715 wh, or 57.2AH. However, before you trash the battery, try doing the test this way. Charge the battery, unplug it and let it sit over night. Then run your fridge overnight. Then turn everything off and see what the voltage is at that point.
Tom

[TimC]

... However, before you trash the battery, try doing the test this way. Charge the battery, unplug it and let it sit over night. Then run your fridge overnight. Then turn everything off and see what the voltage is at that point.
Tom

Thanks Tom. Im still learning how to interpret these ammeters. I won't give up yet. Will charge today. Let sit until Sunday afternoon then run the fridge overnight. I never run everything like that. Fridge and a couple case fans, maybe one light instead of four. I guess a typical draw rate would give me better results instead of a quick drain. I see Will P doing fast draws and thought that's the way to do it. Maybe he's working on batteries than are designed to take that kind of "abuse".

Before recharge and after a little more than 12 hour rest the voltage improved. Does that mean I have used very little of the capacity? Maybe less than 10%?

[TimC]

... ( but a bigger wire between the battery and the fridge might help with that...
Tom

I read that somewhere else as well. Easy part is from my fuse panel to the dedicated APP outlet. I probably have 18awg in that run which is probably only a foot long. What I'd like to see is if I can replace the power cord that came with the fridge. It is excessively long for my purpose and looks like it is just 18awg zip cord. The fridge has a special plug on the fridge end that I would have to rewire unless there is a replacement available. The fridge is out of warranty so maybe I'll install an APP outlet in the case and make my own cord out of 12awg SO cord with APPs on each end?

[Socal Tom]

... However, before you trash the battery, try doing the test this way. Charge the battery, unplug it and let it sit over night. Then run your fridge overnight. Then turn everything off and see what the voltage is at that point.
Tom

Thanks Tom. Im still learning how to interpret these ammeters. I won't give up yet. Will charge today. Let sit until Sunday afternoon then run the fridge overnight. I never run everything like that. Fridge and a couple case fans, maybe one light instead of four. I guess a typical draw rate would give me better results instead of a quick drain. I see Will P doing fast draws and thought that's the way to do it. Maybe he's working on batteries than are designed to take that kind of "abuse".

Before recharge and after a little more than 12 hour rest the voltage improved. Does that mean I have used very little of the capacity? Maybe less than 10%?

Will is testing LiPo batteries, they can take higher draw rates vs deep cycle batteries. Deep cycle LFAs do best with a slow discharge. If you didn't do any charging and it came back up to 12.6 volts, then yes, it seems like there is still quite a bit of capacity in the battery.

... ( but a bigger wire between the battery and the fridge might help with that...
Tom

I read that somewhere else as well. Easy part is from my fuse panel to the dedicated APP outlet. I probably have 18awg in that run which is probably only a foot long. What I'd like to see is if I can replace the power cord that came with the fridge. It is excessively long for my purpose and looks like it is just 18awg zip cord. The fridge has a special plug on the fridge end that I would have to rewire unless there is a replacement available. The fridge is out of warranty so maybe I'll install an APP outlet in the case and make my own cord out of 12awg SO cord with APPs on each end?

18ga is probably too small. for the length you want to consider both legs of the circuit. If I guesstimated right when you did the first test you were pulling about 12 amps. I'm gonna guess the distance from the battery, to the panel, to the fridge is probably 4 or 5 feet of wire including the cord, and the distance back to the battery is another 4 or 5 feet. The the electric blanket might even be a bit longer, I suggest you upgrade that wire to at least 12ga, and probably 10. How are your grounds running back to the battery?

I used this page as a guide for the wire sizing
https://www.boatus.com/expert-advice/ex ... -wire-size

Tom

[TimC]

... I'm gonna guess the distance from the battery, to the panel, to the fridge is probably 4 or 5 feet of wire including the cord, and the distance back to the battery is another 4 or 5 feet. The the electric blanket might even be a bit longer, I suggest you upgrade that wire to at least 12ga, and probably 10. How are your grounds running back to the battery?

Tom

So you got me thinking and I measured the OEM cord for the fridge. It is 16awg and including about 6" inside the fridge case it is 11' long. I started to prep some wire for an APP outlet on the fridge case and was thinking about how long to make the new cord. I keep the fridge on the bed most of the time and have an additional APP outlet in my galley so I'm thinking four feet will be good. I have some 14awg that I'm going to try. If I had 12awg I'd build with that instead but I think 14 and 4' long will be a enough difference. I'll document the install of the APP with a couple photos in case anyone wants to check it out.

Battery to fuse block to the fridge APP outlet is probably no more than three feet. I haven't looked at that wire gauge.

Thanks again for the help and suggestions.

[TimC]

Recharged the battery bank until the NOCO 7200 told me it was pretty much done. Then a good eight hour rest and the battery has settled in at 13.1v

While that was resting I made a replacement for the OEM 16awg cord on my 12v fridge. The old cord was 11' long. The new 14awg cord is about five feet long with an APP on each end. I installed an APP outlet on the fridge and instead of removing the original OEM plug outlet I just spliced into the wiring just inside of the OEM outlet. The wire nuts aren't real elegant but each one has a tie wrap around the three conductors, then good 33+ electrical tape and another tie wrap to secure both hot and neutral.

I don't know if the 14awg is going to make a big difference but the combined length and bigger gauge should help. I had all the components so it was really a quick upgrade. The ammeter is reset to zero watt hours and I have a backup ammeter to verify the numbers. I'll leave the fridge plugged in until it kicks out with a low voltage cut off. It's only pulling around 50 watts when running and typically uses an average of 14 aHr/day last time I checked. This could take a while but at Tom's suggestion I want to do a slow draw more like what a typical camping trip will draw. I'll kick on my ventilation fans each night for about eight hours and maybe a light now and then.

I'll also be able to check the average aHr per day again and see if the original numbers are valid. They should be close and others here on tnttt have verified that their 12v fridges of similar size pull around that much power in a day.







Note to anyone who may do this cord update... while you are in there if you have any rattles or other fan noise now is the time to secure things with some tie wraps. After I bought my fridge I had a small rattle and discovered one of the copper tubes in the fridge was touching the fan mounting frame and would vibrate when it fired up. I put a small piece of foam between them and tied it in place. Easy fix and now a very quiet fridge (It's usually right there next to me while I sleep and I can barely hear it now.

I'll update this in a few days to see if my battery bank capacity test reveals anything new. If you see a situation that makes you think "What the hell is is doing that for?" let me know. I don't claim to be an expert and you shouldn't remove the shroud on your fridge if you are not comfortable with it.

[DrewsBrews]

https://www.youtube.com/watch?v=ija2LmLVZHA

Neat comparison vid, but they talk about general voltage drop issues @~11:15 and some wiring change examples @~22:15

[TimC]

https://www.youtube.com/watch?v=ija2LmLVZHA

Neat comparison vid, but they talk about general voltage drop issues @~11:15 and some wiring change examples @~22:15

Interesting! He really likes 12v fridges doesn't he?

I've switched most of my power cords to APP. They just work without falling out. I had a bad experience with the old cigarette lighter plugs falling out under the lightest of road vibration. I now use the Powerpole plugs for almost everything that has a power cord (shower pump, fridge, portable fans). My solar plugs are set up with Anderson SB plugs because I originally used a portable solar system and it was plugged in and out a lot so I thought SB would handle that better. Now that I have 200 watts on my roof I almost never unplug. If I ever replace those I will use APPs.

[TimC]

OK, that didn't take long to drain the battery! 8 1/2 hours to go from 13.1v to 10.6v with a total of 121 watt hours used. 103 watt hours of that was used by the fridge. I'm going to connect the fridge to 120v through my kill-a-watt meter tomorrow and make sure it is not causing problems. I doubt there is an issue as it was only pulling around 50 watts when it was running.

The fridge faulted at around 10.6v and shut down. I verified the current voltage on the MPPT charge controller, the two ammeters and the in-line ammeter on the cord feeding the fridge. I shut down all the loads (two case fans and one light) and will check in the morning for a voltage reading. I suspect something around 12.2 after it rests overnight. So my conclusion is it is past time to replace the battery bank.

I spent the evening cutting down the depth of the two drawers that the bank sits behind. I'll probably go with a 100 aHr battery and most of the offerings are just a tad too wide for the space. I'll start with one and save up some funds for another later this fall or next spring. I don't remember the reason I went with eight 18 aHr batteries after I built the camper. It must have been a really good one though...

[lfhoward]

That’s an interesting experiment with the fridge wiring. I have an Alpicool fridge with the same connector and probably the same thin long cord. There is definitely a voltage drop involved. I wonder how much power it gives back with the shorter, thicker wires? Will be watching to see once you get your new AGM sorted.

[TimC]

The upgraded wiring for the 12v fridge didn't tell me anything. I'm sure it helped but it's hard to see it under the circumstances.

12.2v battery bank after a 10 hour rest. I'll end the testing and declare the bank dead.

[Socal Tom]

Yep, something isn’t right with that battery.