Amp Hours in a Battery

[Fred Mc]

My house battery system has 2-12 v. marine deep cycle batteries which I think means its not a true start battery or deep cycle.
So to try and determine the capacity I ran a fan on my converter that draws 55 watts(according to my Killowatt gauge) So I ran it for an hour which should work out to 55 watt hours which is about 4.5 amp hours. However my Balmar Smartgauge showed that the battery capacity went from 100% to 82%. So something is amiss somewhere. Is there a way to determine the amp  hour capacity in a battery or/or can the battery store do it?

Thanks

Fred

[richard5933]

Have you tried looking up the make/model online to see what you can find? Most every battery made in recent days should have data posted somewhere.

As a side note, I've found that meters/gauges attempting to read out the state of charge are really useless and not very good at doing their job. On most, they'll show a lower number while the load is drawing current and then bounce back up after the load is disconnected. I try to watch the Ah which we consume as a fuel gauge of sorts - but having that work depends on knowing how many Ah total are in your batteries.

[neoneddy]

Yeah, look up the brand / model and get the amp hour rating. Or you can convert "reserve time" into amp hours. It's a similar standard measurement.

Then get a shunt based monitor if the one you have isn't . If it's using voltage , it's an educated guess at best.

Last thing to consider is , amp hour rating is at a 20h rate usually. So of you run 2x that rate you'll actually see up to 30% less capacity. Likewise if you run at a 40 hour rate, you'll see 10-15% more capacity.

[Fred Mc]

Looking up the specs only tells you what the battery SHOULD have when new.
And the Balmar Smart Gauge doesn"t use a shunt  and supposedly can read the amount left in the battery in %.

Some people feel the only way is to count amps in and  amps out but according to tests and reports I have read (https://marinehowto.com/smart-gauge-battery-monitoring-unit/ ) the Smartgauge determines the reserve other ways.

But, regardless which gauge I use I have to know where I'm starting from .Maybe the batteries are no good.

[neoneddy]

That's a good question. I think testing of specific gravity can get you in the right direction.

If you have the time to use the battery then let it rest 24 hours you could get an idea of it's capacity.

I'd say I've it should charge to 14.5 v or so for a few hours minimum ( if 12v) then figure a load that should be a 25% Depth of discharge, or whatever number works for you.  Run the load then stop when complete. Let the batteries rest 12-24 hours then take a voltage measurement.  Then compare to a chart on voltage to remaining charge chart.

Only other way would be to do a CCA test at an auto parts store. I talked to a guy at the rally this weekend, he swore by the desulfater you can buy on Amazon as a way to restore capacity.

[buswarrior]

Fred Mc,

How long has the Balmar Smart Gauge been installed in the system?

It needs a number of cycles to "learn" the batteries.

I would continue with a week of cycling, various loads, and recharge to full.

Then see where it all drifts to?

There are proper procedures for measuring a battery set that aren't worth doing for this pair.
Compass Marine has a lot of technical articles on electrics that apply just as much to a busnut as they do to a sailor.

Not much can beat a Balmar Smart Gauge for being idiot proof, both in install and in useful information to make decisions about charging and loading your electric system.

happy coaching!
buswarrior

[Fred Mc]

The smartgauge has been in for a while and has been through enough cycles to be accurate...i like it because its easy to monitor but also for the technical aspects of it. It does all the technical things behind the scene so i dont have to.
My next step is to chkekc the s.g. With a hydrometer to try and ascertain if im dealing with good batteries or not.

Regards
Fred

[Geoff]

I know my house batteries are bad when they go dead in a few hours. 

[Dave5Cs]

My Magnum Hi bred inverter lets me know by shutting off the inverter starting the charger and a red light will come on and tell me low batteries. You can set it for what you want to be low battery or use the pre-programed one. 

[Geoff]

My Magnum Hi bred inverter lets me know by shutting off the inverter starting the charger and a red light will come on and tell me low batteries. You can set it for what you want to be low battery or use the pre-programed one.

Yes, that is what I meant-- my Trace SW2512MC also cuts off the batteries before they get to an unsafe charge, which can be adjusted.  The Magnum is a nice inverter, but the Trace has a much better digital readout.
Geoff

[Fred Mc]

"I know my house batteries are bad when they go dead in a few hours. "

Im trying to determine that point at home rather than discouver it at 4 in the afternoon while camping.😀😀😀

[Dave5Cs]

Geoff magnum has a Digital readout on my remote that can hookup to the internet and get upgrades as they come out provides everything you need to run the inverter and the 120 amp charger. Can even remotely start the genny if needed or automatically if I want it too but don't set that feather just in case the genny had a problem And we weren't there. here take a look.

https://www.magnum-dimensions.com/sites/default/files/MagDocs/64-0030-Rev-C-ME-ARC_CD_Web.pdf

[tuccitown]

Man I love my Magnum inverter but couldn't justify the $$ for the remote monitor.

https://www.amazon.com/Magnum-Internet-monitoring-automatic-generator/dp/B00CWX0NJG/ref=sr_1_1?ie=UTF8&qid=1534376718&sr=8-1&keywords=ME-MW-W

Jack

[Dave5Cs]

Jack  for what we saved on the original unit at the time it just made sense to get it for the updates alone and it was only 222.00 when it first came out now it has gone way up.

[richard5933]

We're using the Victron battery monitor, model BMV 712. I went with this one because it has the Bluetooth connection built in which makes adjusting the settings very easy through a smart phone. https://www.victronenergy.com/battery-monitors/bmv-712-smart

I find that the amp usage metering is pretty spot on, and it also will monitor the voltage on a secondary battery bank. Of course, you'll need to know the amp capacity of the battery bank and use a shunt between the ground connection on the battery and the rest of the system.