battery voltage under load ?

[coolerinfrederick]

since i put my 3) 200 ah batteries in my van i watch the volt meter like a hawk, i have a ctek d250sa and smartpass 120 for charging and a powermax pm4 converter/charger when im home, so when my voltage drops below 12.3 with " no load " on the batteries I'll plug in the powermax, i dont drive the campervan much throughout the week but very satisfied with the ctek for charging when i do drive, anyway the other day i was working in the van and decided to see if my 1000 watt inverter could run my 5k btu window unit i installed, and to my surprise it handled it like a champ, ok l thought lets plug in the 115v 1.7 cu ft fridge, and again handled it like a boss with both appliances on, once it cooled down alittle the amp draw from the inverter on the 12v side was only 19 amps and the appliances began to cycle with no issues ( note i have hard starts on all the appliances ), after about 3 hours of running and cycling etc. etc. i noticed while " both appliances were on the voltage would drop down to 11.8-11.9, the inverter never faulted but i didnt like to see it drop so low, i decided to turn the inverter off,,, with no load on the batteries after about 45 mins. the volts came back up to 12.4, hmmm i was about to fire up the generator to recharge when i saw 11.8, but when i shut everything off and let it stabilize i still had a decent charge ( 12.4 volts ), im trying to create a pattern of when to charge ( solar is coming next year ) manually or basically through the powermax, i always look at no load volts, at 12.3 i plugin the powermax and im good but maybe im all wrong here, secondly, why did volts drop so low when the ac and fridge were on even though i still had like a 70% charge on the battery and is it bad for them ?

 

[John61CT]

Wow hard to read all that with no whitespace,

Volts are a very approximate indicator of SoC.

A cheap AH counter would help you avoid going below 50% too often for good longevity

without stopping too early and wasting capacity.

Link to your Powerwerx?

 

[highdesertranger]

charging should be done as often as possible. everyday is best. if you let the battery sit on a partial charge it will negatively effect the life of the battery. highdesertranger

 

[Canine]

Very good to keep a float on them for a few hours whenever possible as well. Just because you have a green light saying it is full, doesn't mean you should take off the charge. FLA type of batteries like to be on float for a while to get a full charge as possible. I'm not sure if this answers your question as I didn't take the time to read the whole post.

 

[MrNoodly]

I get nervous when my batteries get down to 12.5V. But that's just me.

 

[coolerinfrederick]

12.5 is like an 80% soc and is really not necessary to charge at this point, I’ll make it a short question, why did my batteries voltage drop to 11.8 under load and at what voltage under load is unsafe for them ?

 

[MrNoodly]

11.9V is a 50% charge at 60°F. It's 12.06V at 70°, 12.16V at 80° and 12.26V at 90°.

 

[skyl4rk]

The voltage drop under load is related to the physics and chemistry of a lead acid battery. The no load voltage is an OK reference point but there are meters that will tell you much more about your battery status.

 

[John61CT]

And is something **completely** different if there has been a load or charge current applied.

Full resting voltage requires isolation for 12-72 hours.

The voltage-SoC correspondence varies by battery model.

And changes for a given bank as it ages.

 

[skyl4rk]

http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

mod edit, the above link takes you to battery university's article on measure state of charge(SoC). it's a good read.

 

[Weight]

With lead acid chemistries, yes it is proper to charge when 80%. That chemistry is designed to be fully charged. The problem users have is the battery never gets charged much above 80% using what most have for recharging. If not always on mains, you will like solar.
How low you read voltage across your battery is a result of how much draw you have. 50 amps will be different than 100 amps. Voltage drop is not a way to check SOC.

 

[John61CT]

http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

mod edit, the above link takes you to battery university's article on measure state of charge(SoC)

I have found that site contains a lot of over-generalizations and outright errors.

An excellent resource for general noob orientation and terminology, not so great for precision and implementation details.

 

[John61CT]

DC Electrics 101 thread https://vanlivingforum.com/showthread.php?tid=28197

And Frater's wiki site