BBQ! (Basic Battery Question)

[Urlauber]

Certainly more elegant and sophisticated, yes.

It seems that over time, I am getting the hang of this based on the voltage.
For example, it is evening and I see 12.6V, I'm happy and have a drink. If I see 12.4, I know I need to check in the morning and make sure it's still at 12.2 or above. If I see 12.3, I need to consider turning down the fridge. Etc etc, it becomes sort of second nature. Every evening I sort of predict what it will be in the morning and over time I get better and better at that.

Thing is, fridge and (in Winter) heater are my two main energy consumers, and both cycle... so the predicted longevity based on the current current is never correct... unless there is a way to average the last couple of hours.

[Urlauber]

Originally Posted by SteveJ

We've been using a monitor similar to this(there are several that appear identical under different brand names), in our Trek. We do boondocking for up to 2+ months at a time without plugging in. I've noticed no creeping of WH available. from what I've seen there is no provision to allow for the Peukert effect but it does reset so no apparent issue. For the low $$ it works fine with our two group 31 FLA batteries, I think.

https://smile.amazon.com/AiLi-Voltme...s%2C178&sr=8-3



We used two of the cheaper one way coulometers(one for each direction of current flow) in the RT which did have a building spread in the WHs in/out.

Link:

https://smile.amazon.com/bayite-6-5-...%2C178&sr=8-34

Have fun, y'all.

I finally stopped the procrastination and purchased the coulometer linked above. So thanks everyone and especially Steve, wouldn't have done it without you.

Squeezed myself under the van, found the negatives, constructed a copper piece to screw the shunt against the chassis, and connected all the wires. Seems to be working so far. Tomorrow I will charge up the batteries and set the 100% point.

Will need to figure out how to protect it from the elements. I kinda like zipper bags, duct tape and zip ties. 🤫

[Urlauber]

I may need some help from the experts...

So I connected the shunt and monitor pictured above. Seems to be all functional.

Then I set the capacity to 200Ah according to the two 100Ah batteries in the camper.

Next I fully charged them via the solar panel, ending up at 13.6V. I set the capacity gauge to 100%.

Disconnected the charging, voltage went to 13.2V.
Put a mild load on it (1-3A), voltage dipped to 12.8V.

So it has been discharging for almost a day, and it is now showing 80% capacity, or 160Ah. However, the voltage is 12.4V, again, between 1 and 3A are being drawn.

Does this sound right? I guess if I remove the load the voltage will go up slightly. I am going to let it discharge further (50%?) and see what the voltage is then.

There are options to set a voltage on the meter to indicate "battery empty", not sure if that would be truly empty, or the much discussed 50% mark. I guess that depends on whether I want to see the gauge reflecting the capacity I want to pull out of them, or the full capacity. Not sure.

Also, when they say "fully discharge the battery" - what does that mean? 11.65V at open circuit? So discharge them more then that, then remove the load and let them sit to reach the 11.65? Isn't that bad for the batteries?

[booster]

Originally Posted by Urlauber

I may need some help from the experts...

So I connected the shunt and monitor pictured above. Seems to be all functional.

Then I set the capacity to 200Ah according to the two 100Ah batteries in the camper.

Next I fully charged them via the solar panel, ending up at 13.6V. I set the capacity gauge to 100%.

Disconnected the charging, voltage went to 13.2V.
Put a mild load on it (1-3A), voltage dipped to 12.8V.

So it has been discharging for almost a day, and it is now showing 80% capacity, or 160Ah. However, the voltage is 12.4V, again, between 1 and 3A are being drawn.

Does this sound right? I guess if I remove the load the voltage will go up slightly. I am going to let it discharge further (50%?) and see what the voltage is then.

There are options to set a voltage on the meter to indicate "battery empty", not sure if that would be truly empty, or the much discussed 50% mark. I guess that depends on whether I want to see the gauge reflecting the capacity I want to pull out of them, or the full capacity. Not sure.

Also, when they say "fully discharge the battery" - what does that mean? 11.65V at open circuit? So discharge them more then that, then remove the load and let them sit to reach the 11.65? Isn't that bad for the batteries?

I assume we are talking about AGM batteries at those voltages??


If so, it is highly likely they were not anywhere near full from the charging. It can take upwards of 10 hours of absorption time to get there.


What solar controller do you have and what are the charge settings? How do you "know" the batteries are full?



Most controllers are lucky to get to 80% full as they limit absorption time to prevent overcharging. If the batteries have been chronically undercharged they could already have reduced capacity.

[Urlauber]

Correct, two Trojan Grp31 100Ah AGM batteries (as described in the OP).

That's a good point! The SCC is a GoPower 30A PWM 30SQ controller, set to the AGM charging profile.

I'll let them run down to 50%, take note of the voltage under load and open circuit, and then go through a full absorption charge and after that set it to 100% and try again to compare.

[booster]

Originally Posted by Urlauber

Correct, two Trojan Grp31 100Ah AGM batteries (as described in the OP).

That's a good point! The SCC is a GoPower 30A PWM 30SQ controller, set to the AGM charging profile.

I'll let them run down to 50%, take note of the voltage under load and open circuit, and then go through a full absorption charge and after that set it to 100% and try again to compare.

I don't think that will necessarily fix anything because many/most solar controllers don't really know if the batteries are full when they go to float because they use voltage, time, or an algorithm to determine full batteries and those methods can be hugely inaccurate. I will have look to see what the GoPower uses for charge control, but if you are not in absorption for about 6-8 hours at full voltage you are very likely not getting full and will be somewhere in the 65-90% full range depending on the time you were in full voltage absorption.


on edit, I just found a spec sheet on that controller that lists absorption as 1-2 hours total per day. You are almost certainly running somewhere considerably short of full batteries, probably in the 80% range.


I just looked at the manual and they list a different spec for absorption time. They say 14.9 amps but that would be too the coach not necessarily the batteries alone so actual could be anything under that to the batteries. 1.9 amps is like 7.5%C for 200ah of batteries so way too high to be fully charged. AGMs will normally be taking 1%C or less at fully charged.



The also list a 4 hour absorption timer so that must be the max time per day in absorption and it is about 1/2 of what you need to get full from 50% down. They do that to prevent severe overcharging of batteries that are full when solar activates.

[Urlauber]

The manual for the GP-PWM-30-SQ does not specify for how long it does the absorption charging... Until full.

OK, I see your edit. Not that I understand all of this. I know the output of the single solar panel maxes out at about 10A. This may be too low for a proper, quick, full charge, but I thought that this just means that it will take a bit longer to fill them up.

[booster]

Originally Posted by Urlauber

The manual for the GP-PWM-30-SQ does not specify for how long it does the absorption charging... Until full.

OK, I see your edit. Not that I understand all of this. I know the output of the single solar panel maxes out at about 10A. This may be too low for a proper, quick, full charge, but I thought that this just means that it will take a bit longer to fill them up.

You are pretty close on your thoughts on the size of the solar. If the panel could do 10 amps continuous and the batteries had a 100% charge efficiency, it would take 10 hours to recover 100ah. Both are not going to happen in the real world though. You usually get about 4-5 hours of high sun a day and panels never run at max output besides. The charge efficiency will be near 100% up about 80% full at 10 amps into a 200 amp bank, but you won't have 10 amps so it will take a lot longer. The last 20% of charge on AGMS is going to take 6-8 hours no matter how many charging amps you can supply because the batteries won't accept much in the last 20% of the charge.

[SteveJ]

Originally Posted by Urlauber

I finally stopped the procrastination and purchased the coulometer linked above. So thanks everyone and especially Steve, wouldn't have done it without you.

Squeezed myself under the van, found the negatives, constructed a copper piece to screw the shunt against the chassis, and connected all the wires. Seems to be working so far. Tomorrow I will charge up the batteries and set the 100% point.

Will need to figure out how to protect it from the elements. I kinda like zipper bags, duct tape and zip ties. 🤫

Congrats. I used a semi flexible plastic 8oz deli container with the lid that came with it. I cut a whole in each side to run the cables to the shunt placed inside then snapped the lid on it. I placed mine on the top of the battery with the negative to ground connection.

[Urlauber]

Originally Posted by SteveJ

Congrats. I used a semi flexible plastic 8oz deli container with the lid that came with it. I cut a whole in each side to run the cables to the shunt placed inside then snapped the lid on it. I placed mine on the top of the battery with the negative to ground connection.

Ha, thank you!

I installed it a bit differently, by hammering a piece of copper pipe flat, bending it, drilling it, and using it to attach the shunt to the point where a bunch of the negative wires were screwed to the chassis. Because my van has two batteries which are not easily accessible this was my solution. No plastic container, but I'll figure out something.

So, after setting the monitor to 100% yesterday, I used up 100Ah which left it at 11.99V (under load 5A), After disconnecting it went up to 12.20V which, according to the rainbow chart posted earlier, would be ~65% SOC. This seems a bit too good to be true, so I dunno. In any case, tomorrow I will charge them back up and see if anything changes, and then just keep monitoring to get a better understanding of how voltages and SOC associate with each other.

[Blueboy1]

Originally Posted by Urlauber

Certainly more elegant and sophisticated, yes.

It seems that over time, I am getting the hang of this based on the voltage.
For example, it is evening and I see 12.6V, I'm happy and have a drink. If I see 12.4, I know I need to check in the morning and make sure it's still at 12.2 or above. If I see 12.3, I need to consider turning down the fridge. Etc etc, it becomes sort of second nature. Every evening I sort of predict what it will be in the morning and over time I get better and better at that.

Thing is, fridge and (in Winter) heater are my two main energy consumers, and both cycle... so the predicted longevity based on the current current is never correct... unless there is a way to average the last couple of hours.

I have installed this unit 6 years ago and it is very useful. Since it displays the energy used (Watts) it is quite easy to figure out your overnight consumption.
It has also a low/high voltage alarm that you can set. A bit on the cheap side but it works, along with your solar controller display, you will have all the information needed
https://www.amazon.com/MNJ-Motor-Mul.../dp/B07JJWL62G

[Urlauber]

Originally Posted by Blueboy1

I have installed this unit 6 years ago and it is very useful. Since it displays the energy used (Watts) it is quite easy to figure out your overnight consumption.
It has also a low/high voltage alarm that you can set. A bit on the cheap side but it works, along with your solar controller display, you will have all the information needed
https://www.amazon.com/MNJ-Motor-Mul.../dp/B07JJWL62G

From what I have learned over the last few months, I would say that unit is missing the SOC display provided by a Coulometer like the one Steve recommended. Wattage and Whrs are certainly useful, but in the greater scheme of things, it is nice to have a quick look at the display and know how empty your batteries are, how many Ah you need to add to fill them to 100% etc.

Also, 100A may be just a bit on the low side. Things like starting the generator may exceed the rating, even if just for a few seconds.

As Harry says so succinctly in post #2.

[booster]

Originally Posted by Urlauber

From what I have learned over the last few months, I would say that unit is missing the SOC display provided by a Coulometer like the one Steve recommended. Wattage and Whrs are certainly useful, but in the greater scheme of things, it is nice to have a quick look at the display and know how empty your batteries are, how many Ah you need to add to fill them to 100% etc.

Also, 100A may be just a bit on the low side. Things like starting the generator may exceed the rating, even if just for a few seconds.

As Harry says so succinct in post #2.

The thing to remember with any of the low cost, simple, monitor/counters is to be sure that there is a way to calibrate them after charging but before discharging, preferably automatically during use, but also manually if needed. Many of the low end units don't do that and also can't be set for charging efficiency and that can make accuracy even worse over time.

[Blueboy1]

Originally Posted by Urlauber

From what I have learned over the last few months, I would say that unit is missing the SOC display provided by a Coulometer like the one Steve recommended. Wattage and Whrs are certainly useful, but in the greater scheme of things, it is nice to have a quick look at the display and know how empty your batteries are, how many Ah you need to add to fill them to 100% etc.

Also, 100A may be just a bit on the low side. Things like starting the generator may exceed the rating, even if just for a few seconds.

As Harry says so succinctly in post #2.

Just for the information , the unit does display SOC, and most battery manufacturer do provide SOC chart for their products, but I do not want to start an argument , just adding infos Have a nice day

[Urlauber]

Oh, I missed that. So it counts the Wh's up and down correctly? That is cool, for the price.

[booster]

AH both up and down is just as useful, maybe more, to me that a SOC reading the is just a calc off of the AH reading.

The big deal to me is if the counter resets based on getting a confirmed full charge so it stays accurate over time and isn't going more and more inaccurate because of charge efficiency.