Issue with House Batteries

[DaveBad]

I have a 2007 Great West Van Classic. When I bought it the batteries were toast. I replaced them with 2 AutoCraft Marine Batteries, Group size 27M. The batteries for the most part have been well taken care of. Removed from the van every fall, fluid level checked and placed on battery tenders for the winter. I installed the batteries a couple of weeks ago and have not put them to use yet.
https://shop.advanceautoparts.com/p/...dc-2/2080036-P

I have a 130watts of solar power connected to a 20 AMP MPPT Controller. The controller shows the battery at 100%. When I turn on the fridge to put a load on the batteries the battery display drops down quickly (in 15 seconds) to 50-45%. When I turn the fridge off the battery display slowly climbs back up.
The attached images were taken while doing the load test for a third time. I have ordered a hydrometer to check each cell.

Any Thoughts?

Dave

[rowiebowie]

What you're seeing may be a tad extreme, but not unusual for voltage to drop quickly under a heavy load and then recover nearly as quickly.

When you say turn on your fridge, is it a compressor fridge? If so, this shouldn't happen as it should only draw 3-4 amps.

But if you are operating an absorption fridge on 12volts, then that may be a severe enough stress to cause what you are seeing. I don't know what the draw is in this case, but pretty large I'd guess.

[markopolo]

Is that 12.6V no load after a few tests and 10.5V with a 100 amp load from the load tester?

If so, they seem OK to me.

Some info about the fridge as Rowie noted would be good to have.

Do you know what the battery voltage is at when the display shows 50-45%?

[DaveBad]

Its a Dometic3-way fridge. Model RM2354.

Hmm, using 12V draws 14.6Amps. That seems like a lot. WE never run the fridge off the batteries.

Absorption Fridge

[booster]

For gp27 and an absorption frig on DC power, that is likely not all that bad as all you are reading is voltage and the frig will drop it some as it will be 10-15 amps. You are seeing about 2v so kind of on the edge. Most of the "marine" batteries are not really deep cycle which tend to not be nearly as durable as golf cart batteries and you may only get 2-3 years on them in use. That is about what we saw on our Roadtrek that had similar batteries.



You are starting at about 12.6v if you can believe the meter which may not be right on (it is Harbor Freight). 12.6v is not all that bad for that kind of battery in most cases. You may find the the specific gravity to also test a bit low even on a good battery. I usually see no more than about 1260 on them with temp correcting hydrometer (EZRed) and often lower.


Best thing to do would be a true capacity test. Put on a relatively small load and run until you get to the 10.5v limit and see how long it has run. It is a good idea to do that test whenever you put in new batteries so they are easy to check later.


As with all of this battery stuff, putting in a shunt based battery monitor is likely the best thing you can do, IMO, as then you will know for certain what is going on.

[Rockwood27]

Originally Posted by DaveBad

Its a Dometic3-way fridge. Model RM2354.

Hmm, using 12V draws 14.6Amps. That seems like a lot. WE never run the fridge off the batteries.

Absorption Fridge

That seems right. If you look at the 120V draw, it's 1.5A, or 1/10 the 12V draw. I use to run my refrigerator on 12V and had the inverter on to charge laptops and phones while driving. My twin, 6V AGM batteries would die...the engine alternator couldn't keep up. I switched the refrigerator to LPG and the issue went away. 2012 Roadtrek 190P on Chevy Express.

[DaveBad]

So as asked previously.
After putting a load on with the fridge for a short time and applying the the load tester 3 times after about an hour with no charging applied my digital volt meter reads 12.8 volts.
The thing that I don't understand is why the charge controller is displaying the battery at 75%. Before applying the loads it was at 100%.

https://www.renogy.com/rover-li-20-a...ge-controller/

The Harbor Freight Load tester was bought years ago when I was trying to determine if my car had a bad battery or a drain.

Dave

[markopolo]

On your Renogy unit:

The Battery Capacity (SOC%) is estimated based on the charging voltage.

So when a load, even if temporary, pulls the voltage down the SOC estimate also drops. It's not an actual shunt based amp hour counting SOC meter.

[DaveBad]

Thanks for all your input. I was concerned that I may have to go out and get new batteries. They seem like they're pretty healthy for now. We don't do a lot of boondocking but I like to have some power when we are away from shore power for a few days. We run the fridge on propane.

When these die I will be searching for some true Deep Cycle batteries. The 6V's I've seen are to tall for my compartment. My max height is 9", depth is about 13" and my total width that fits 2 batteries is 14".

Thanks Again, Dave

[eric1514]

Originally Posted by DaveBad

So as asked previously.
After putting a load on with the fridge for a short time and applying the the load tester 3 times after about an hour with no charging applied my digital volt meter reads 12.8 volts.
The thing that I don't understand is why the charge controller is displaying the battery at 75%. Before applying the loads it was at 100%.

https://www.renogy.com/rover-li-20-a...ge-controller/

The Harbor Freight Load tester was bought years ago when I was trying to determine if my car had a bad battery or a drain.

Dave

I have that solar controller and a Trimetric battery monitor. I'm not sure how the Renogy controller arrives at it's number for battery charge status. You can set the capacity on it but it really has no idea of how many Ah you've taken or replaced with some other charging source like a converter plugged into shore. In short, I think it's a terrific controller and a horrible battery monitor. I trust my Trimetric to tell me what's really going on, including what the controller is doing.

[booster]

Originally Posted by eric1514

I have that solar controller and a Trimetric battery monitor. I'm not sure how the Renogy controller arrives at it's number for battery charge status. You can set the capacity on it but it really has no idea of how many Ah you've taken or replaced with some other charging source like a converter plugged into shore. In short, I think it's a terrific controller and a horrible battery monitor. I trust my Trimetric to tell me what's really going on, including what the controller is doing.

Your Trimetric should be able to tell you if the Renogy is doing a good job of charging, which would be interesting to me as they are very sketchy as to how they determine the battery is truly full but not over charged.


Would you be able to post the Trimetric settings you have for the transition to float amps or % whichever it uses, the battery bank size setting and the maximum/minnum time in bulk/absorption. Also what style and brand of batteries you have. That will tell you if the batteries are really being charged to full on not too full. If set right, the Trimetric should show full charged light at the same time the Renogy is going to float if it is doing it correctly. I am always looking for charging sources that do a good job of complete charging without a shunt, but it is very hard for them to get right, it appears. I fear they may have an issue if they don't really know what the state of charge is as that is critical to charging.

[eric1514]

To know when the controller transitions to different charge modes would require me to baby sit the thing and I don't see that happening anytime soon but here are some numbers I gathered this morning. I had the refrigerator (NovaKool R3100) on all day and night. When I checked after dinner, the Trimetric said the batteries were at 100%.

This morning at 7am my time, 1/2 hr after sunrise, the Trimetric said the batteries were down 11.2 Ah. I have 210 Ah of AGM battery so 11.2 is about 5% down and the Trimetric said I had 95% and voltage was 12.8. All's good.

The controller on the other hand said the voltage was also 12.8 but that the batteries were at 83%. The controller has no way of reading amps in or out so I don't know how it came to its conclusion. It does know I have 210Ah of battery because I told it so. There was enough light at 7am to produce .4 amps at 17.5 volts according to the controller (the van is completely in the shade at this time of day) but the Trimetric was showing only .1 in the positive going to the batteries. The discrepancy makes sense because of draw by a Trik-l-Start, smoke/propane detectors, the Trimetric, etc.

I pleased with the controller as far as its ability to charge the batteries. It's just not a good monitor. I leave its display showing how many amps are being produced by the panels and I leave the Trimetric set to show me how many Ah I'm down.

[DaveBad]

"Best thing to do would be a true capacity test. Put on a relatively small load and run until you get to the 10.5v limit and see how long it has run. It is a good idea to do that test whenever you put in new batteries so they are easy to check later."

This may be much more info than you want but it does attempt to explain a lot.
It also details exactly how to do a 20hr test and a 2hr test.

https://marinehowto.com/programming-a-battery-monitor/

Dave

[booster]

Originally Posted by eric1514

To know when the controller transitions to different charge modes would require me to baby sit the thing and I don't see that happening anytime soon but here are some numbers I gathered this morning. I had the refrigerator (NovaKool R3100) on all day and night. When I checked after dinner, the Trimetric said the batteries were at 100%.

This morning at 7am my time, 1/2 hr after sunrise, the Trimetric said the batteries were down 11.2 Ah. I have 210 Ah of AGM battery so 11.2 is about 5% down and the Trimetric said I had 95% and voltage was 12.8. All's good.

The controller on the other hand said the voltage was also 12.8 but that the batteries were at 83%. The controller has no way of reading amps in or out so I don't know how it came to its conclusion. It does know I have 210Ah of battery because I told it so. There was enough light at 7am to produce .4 amps at 17.5 volts according to the controller (the van is completely in the shade at this time of day) but the Trimetric was showing only .1 in the positive going to the batteries. The discrepancy makes sense because of draw by a Trik-l-Start, smoke/propane detectors, the Trimetric, etc.

I pleased with the controller as far as its ability to charge the batteries. It's just not a good monitor. I leave its display showing how many amps are being produced by the panels and I leave the Trimetric set to show me how many Ah I'm down.

I think you are missing my point on watching the controller to see when it transitions. This is not something you do on a regular basis. You only do it to determine if the batteries are being charged properly by the controller. IMO, the only decent way to tell if the controller is doing a good job is to look at the amps to the batteries at the transition to float point, while still at the absorption voltage. Essentially every controller that uses an algorithm or pure timers to control the charging will be over or under charging on nearly every recharge cycle, which shortens the life of the batteries. By making certain that a Trimetric is programmed properly to light the "charged" lamp, you have all that information right in front of you on the Trimetric. If you are over or undercharging the batteries, it will shorten the life by some, non quantifiable amount. It all depends on the severity of the over or under charging.



I think a lot of this an issue with how the manufacturers state things about their charging. It is not just solar controllers, but also shore chargers, remote alternator regulators, and B to B chargers as nearly all of them use algorithms or timers, or both. There are very, very few shore or solar chargers that control accurately off the battery charging amps that are actually to the battery, and no alternator ones that I know of.


Some chargers, particularly shore chargers have started to read charging output internally and transition at a predetermined level, sometimes roughly settable. While this is a better setup, it does not account for any power that is being used for running the van. If you have something like a couple fans, lights, tv, compressor frig running, they can lock the charger into absorption until the max timer trips out, almost assuring an overcharge.


Also be aware that the Trimetric saying 100% may or may not mean the batteries are full, that is why I always ask for the settings in Trimetric which have to be met to determine full batteries. The Trimetric needs to get to those to reset to 100% calibration on the next discharge, but on a charge cycle you can see 100% long before the batteries are full, if the charged lamp isn't on.


My point is, as always, that you really don't know how well any charger is taking care of your batteries unless you test it, as the claims by the sellers grossly overstate how accurate they can charge on a regular basis, IMO.

[engnrsrule]

I had a similar experience trying to run my absorption fridge on 12 volt. Mine pulls about 11-12 amps.

I upgraded to two 6v golf cart batteries for 235 ampere hours and do ok now, but even that won't support the fridge much more than overnight. I do not have solar, so recharging requires running generator, getting to a shore tie or moving down the road.

If you are not using a true deep cycle battery (like golf cart batteries) they will not take kindly to the amount of cycling you are subjecting them to.

My protocol is this. If 110 is available, run the fridge on 110. If rolling run it on 12v (including for short stops enroute less than a few hours) otherwise run it on propane.

Good luck.

[Sehc]

Dave. Just the link I was going to post. Rod Collins freely gives much good information. I try to buy things from Rod's store. I am thinking about the new Balmar SG-200.

[engnrsrule]

My golfcart batteries are here, about $150 each. https://www.batteriesplus.com/productdetails/sligc125

They measure 7 x 10 x 11h so too tall for your compartment. smaller sizes may be available.