Need Input...Re Hawk Battery Issue..."On The Road In The Cold"

[Wallowa]

When using furnace and fridge my 2 AGM 75 Ah battery voltage declined slowly from 13.6 V to 10.63 V (Zamp controller showed one idiot light at low voltage) but my BMV indicated a SOC that started at 100% and dropped to a low of 90% SOC....when I turned off the furnace the voltage slowly increased to 12.6 V and SOC went up to 96%...battery temp 26 to 32F...no solar, no sun during this.

Any ideas why the disparity between voltage and SOC?

Since then, battery temp 5F, but with sun/solar and no appliances on...Zamp reads "full" (4 idiot lights) and BMV SOC at 100%....BMV has been scynd with batteries...

I am in Kellogg Id and headed to Whitefish where current temps are well below zero...warming some mid-week...my options are to motel it, use my Honda 2200i or go for broke and see if AGMs will entirely crop out.

Any and all ideas welcomed!

Thanks....Phil "Out In The Cold"

 

[Wallowa]

Oops, can moderator please send this to FWC discussion group?

Sorry
..Phil b

 

[Vic Harder]

Phil, the voltage going back up to 12.6 is reassuring. That would equate to nearly a full charge if the batteries where just sitting there with no load/charge. The drop to 10.63 is scary, given that you have a very low load on the batteries. Nothing if not confusing and scary.

Hoping rando and craig can jump in here....

 

[JaSAn]

My Trimetric does not take temperature into account in determining state of charge.

Lead-acid batteries loose a lot of capacity below 0ºF:


This chart show at what temperature your battery electrolyte will freeze:

 

[Wallowa]

Assuming the SOC was 100% the "freezing temp" is -94F..is that chart applicable for AGMs?

Are AGMs considered "lead/acid" batteries?

And does "capacity" mean Watts?

None of this explains the disparity between the amount of voltage decrease and lower drop in SOC; in short, are my batteries damaged?

Thanks the help everyone...

Phil

 

[rando]

Where was the voltage measurement taken? If you have a bad connection (ie high resistance) to the battery and you have a load running it would cause a voltage drop, giving you an unreasonably low voltage reading. It could also be possible there is an issue with your batteries. While you do loose capacity at lower temperatures, you mentioned your batteries were around 0C, so the capacity loss is small, maybe 10-20% and would not explain what you are seeing.

How old are the batteries?

 

[Wallowa]

Where was the voltage measurement taken? If you have a bad connection (ie high resistance) to the battery and you have a load running it would cause a voltage drop, giving you an unreasonably low voltage reading. It could also be possible there is an issue with your batteries. While you do loose capacity at lower temperatures, you mentioned your batteries were around 0C, so the capacity loss is small, maybe 10-20% and would not explain what you are seeing.

How old are the batteries?

Thanks Rando...'16 Hawk so batteries are at least that old, always in shop with 110/Iota..

Yes, heck of a place to find out batteries are punking..out..it is what it is..BMV712..checked and tightened battery leads before this trip ..voltage on Zamp and BMV equal..

Phil

 

[rando]

When the voltage drops, what is the current that the loads are drawing (the BMV will tell you)? There is a slight possibility that something is drawing more current than it should causing the voltage to sag, but this is unlikely.


If the connections are all good, then a battery issue seems like the most likely culprit. Low temperatures due tend to bring out the latent issues in a battery system.

 

[Wallowa]

Can't remember the BMV load...seems, -2+ Ah...furnace and fridge..

Yup, on batteries...will task the system and see if voltage bottoms...still do not understand why the SOC never went below 90%...

Thanks Again,
Phil

 

[rando]

The SOC is not based on the voltage, it is based on the amps being drained multiplied by the time (ie Amp-hours). Assuming you have 150Ah of batteries, an SOC of 90% means you have pulled 15Ah since the last time it was fully charged. The BMV doesn't know what the actual capacity of your battery is, only how many amp hours you have used.

 

[Wallowa]

OK...I get that SOC is based on amps going in and out of batteries through the shunt...but the BMV was programed with AGM and battery capacity (amps in this case)of 150 Ahs..the Zamp controller I believe "estimates" the SOC purely based on voltage level...wish there was a real-time Watt level meter...


What explains the Zamp (and BMV) voltage of 10.63V but BMV measured SOC OF 90%?

Currently in Whitefish...will not 'test' the system until next week...too cold to ski..while driving here the battery temp was 12F...but zamp @ "full" and SOC 100%...my guess is that if I put a load on the batteries...the voltage will take a dive..meantime found a great motel!

Thanks for leading me through this..

Phil

 

[JaSAn]

AGM batteries are Lead-Acid batteries.

Capacity is watt-hours or amp-hours.

My Trimetric determines SOC based on amps in vs. amps out. BUT that full capacity is not available at temperatures lower than 77ºF.
LA batteries loose 10% capacity at 60º, down to 35% at -0º, and 50% at -22ºF

At lower temperatures battery acid condenses increasing cell voltage. At 0ºF a12V charged battery resting voltage will be around 12.9V. (This is why you need temperature compensation on a battery charger).
At lower temperatures battery internal resistance increases, making the battery work harder to deliver amps, voltage drops faster.
The increased internal resistance and resultant faster voltage drop is the reason you can't utilize all the battery capacity. The capacity is still there (as can be measured by a short circuit), the voltage drop is too big to drive 12V devices.

Your batteries will not be at 100% in the morning after running your furnace all night. I could not find anything that would tell me when a battery would freeze without knowing the SG of the acid mix.

I hope this isn't too obtuse. My brain sometimes outruns my fingers and I miss explaining steps.

 

[Wallowa]

Just lost a reply...JaSAn, thanks..interesting that low temps both raises voltage while increasing internal resistance which "constipates" my AGMs and choaks off the flow of Amps..

My Victron 712 measures the SOC just like your Trimetric, BUT the Zamp guesses at the SOC based on type of battery and the voltage.

So what caused the disparity when the Zamp showed 1 idiot light at 10.63V while BMV showed SOC of 90% at the same 10.63V ? One of them was inaccurate.

Thanks for the help..

Phil

PS...Or was the BMV SOC correct and since the voltage was so low only 10% of the amps could be extracted from the batteries?

 

[ri-f]

It kind of sounds like the plates in one or both of your AGM's are toast or close to it. Seems like it won't hold a charge any longer. You may still be able to charge it up to a fully charged voltage state, say 12.9 volts or so when in the resting state, but when you apply your normal loads next time, the voltage may start to drop unreasonably quickly and before you know it your at 11 volts or in your case 10.6, which would normally indicate a zero SOC. If you disconnect the loads and let the battery rest, the voltage will begin to rise again, but still remain low, like 12.1 volts until you recharge again. 12.6 volts seems like about 75-80% SOC. It just seems like it simply won't hold a full charge and then discharges quickly. It wouldn't be particularly unusual for an AGM to fail after 5 years. They're supposed to go 5-10 years. I've had AGMs that wouldn't hold a decent charge after 2-3 years. I assume you measured the voltage with a good multimeter directly at the battery terminals to confirm the BMV 712? Maybe the SOC reading from your BMV 712 is being fooled by the fact that your voltage is low, but you didn't consume very many amp hours on your way down to 10.6 volts. The BMV was just doing the math (not taking a real reading, like your voltage or current draw. Just a thought.

Rich

 

[Wallowa]

No multi-meter here in Whitefish...and home shop is 400+ miles away...I assume that since the Zamp and BMV show identical voltage values...that the voltage was correct..not certain what else could I measure? Also I thought the BMV does in fact measure amperage flow across the shunt when current flows in or out of the batteries...what am I missing?

Weak/damaged cells seems to unfortunately be my reality...Soooooo.guess it is time to "Adapt, Improvise,Overcome" until I complete my ski trip...

Thanks..for your help...scheduled to Li in June..

Phil

 

[ri-f]

Don't think you're missing anything. measuring with the multimeter only to confirm the voltage directly at the terminals vs through the wires to the other meters. Chances are your meter reading will be the same. Well, a cheap AGM swap out until the new Li, which I'm sure you'll really like maybe in the cards. At least you have your 2000i for now.

Best,
Rich

 

[Vic Harder]

Phil, the SOC is calculated based on the number of amps that flow through the shunt. If the BMV was synchronized after you stuffed 150AH into the batteries, and 15AH have "flowed" out through the shunt, then you will see 90% on the BMV. In the meantime, the batteries appear to have suffered a catastrophic failure and there really are not that many AH left in the battery.

It is like as if you had filled a barrel with 150 gallons of water, and measured that you drank 15 gallons, so you still have 135 gallons right? Not if someone/thing poked a hole in the barrel and the water is leaking out.

What caused the failure? I'm guessing, but perhaps the batteries were weak and they froze when it got really cold?

 

[Wallowa]

Thanks for all the information and support; greatly appreciated...as stated for the remainder of my ski sojourn I will be in a motel (prefer my Hawk) , on the Honda 2200i or in the few available RV spots with 110...too tight to spring for new AGMs 3+ months before Li conversion June 4th...funny but inspite of issues with Hawk, I greatly enjoy my "Hawk Cave"...

Take Care,

Phil

 

[fuzzymarindave]

Too bad I'm not closer, I'd give you my old AGM. I just removed the AGM battery from my 2016 Hawk for my Lithium Ion conversion which I'm starting this week. Maybe you can source an old but usable cheap AGM marine battery near you since there is a lot of boating activity around Flathead Lake. Of course the motel will be more comfy given the cold temps.

 

[Wallowa]

Too bad I'm not closer, I'd give you my old AGM. I just removed the AGM battery from my 2016 Hawk for my Lithium Ion conversion which I'm starting this week. Maybe you can source an old but usable cheap AGM marine battery near you since there is a lot of boating activity around Flathead Lake. Of course the motel will be more comfy given the cold temps.

Fuzzy

Many thanks for the thought and offer...resigned to living off Honda 2200i after leaving Whitefish Sat...hey, this is why they call it an adventure! One eye opener is how much resistance the cold temps cause to raising and lowering the top..hypalon stiffens up..all part of learning curve...

Thanks..Phil