Load Testing a pair of T-105's

The assumption folks in the battery charger community...

"You ain't got the brains to charge a battery right!"

(so we'll fixya up with a high frequency charger that weighs two pounds, uses a guesstimate seventeen cent chip and we'll charge you ten times as much for the Art Deco masterpiece as we paid for it)

If you read Trojan's specs on charging you will find that NO COMMERCIALLY AVAILABLE AUTOMATIC CHARGER MEETS THEIR REQUIREMENTS !

Batteries need several hard cycles to fully permeate the plates with electrolyte. Unless they sit eternities connected to a power pedestal only charging at 14.8 volts until they bubble (generator) can do this. And even with power pole service the only way to verify that they are being fully charged is by dipping with a trusted hydrometer. Usually TOP CHARGING a top quality flooded like a 105 is a good-enough assumption the batteries are prepped for a drawdown test.

Taking them down to 10.5v over 20 hrs would be very hard on the batteries. That is a 100% DOD.

EDIT--I see that was 10.5 loaded when the inverter shut down, so it would have not been as much "resting voltage" after bounce back.

You can get the capacity close enough by just going down to 50%, which is the usual recommended limit. (Of course you can get away with going lower but you aren't supposed to make a habit of it)

It is supposed to be linear for discharging, but I find it speeds up a little from 75-50 compared with 100-75. Got to keep an eye on the SG getting close to 50 or you will overshoot easily.

If using 12v lights as your load, you do have to add another light part way through to maintain the 20 hr rate, as lights dim and draw fewer amps as battery voltage declines. If using inverter as the load, it is the opposite, where the inverter pulls more amps as battery voltage declines. Start with just under the 20 hr rate and end up just over so it averages out roughly, close enough--it doesn't have to be exact for this test to be able to tell how your batteries are doing.

Mine are T-145' s, and I charted them every hour, on the hour from 100% SOC on the Magnum as well as wet bulb, all the way to 10.5v cutoff adjusting a constant 20a draw at each measurement point. Something I wouldn't do very often but now there's a future benchmark on record.

That's good for about 22hrs constant 20A draw

I am one of those that really don't need to know the absolute state of my battery charge state status. I only need to know that I can camp for up to 10-12 days using my Battery bank starting out with a full Charge state set of batteries. Then I will normally draw around 22-24AMPS DC current from 6PM to 11PM each evening when camping off grid in addition to having a 24/7 parasitic drain of 1-2 AMPS all the time.

This will drop down my DC VOLTAGE to around 12.0VDC around 8AM the next morning when I am usually allowed to run my generator to operate my on-board PD9260C 60AMP Converter/charge for around three hours of generator run time. This brings my battery bank back to somewhere around the 90% charge state I guess... All I care about is I do this routine over and over for long camping trips and my batteries will maintain the roughly same performance times. If I don't get them somewhere around 90% charge state to start with then the DC VOLTMETERS drops down to the 12.0VDC reading quicker then it previously did... It gets below the 12.0VDC around 10PM i quit using the batteries and wait until 8AM the next morning to re-charge the batteries.

After doing the so called 50% to 90% charge state cycles for 10-12 days in a roll I then start loosing my battery performance level. I have to stop the 50% to 90% cycle and recharge my battery back for about 12 hours then before I can start doing all of this all over again.

I really don't give a hoot what the absolute charge states are as this works great for me. Been doing it since around 2009 and just last season I was not able to re-coup my battery bank telling I must be getting close to the end of life for my batteries...

Most of my camping off-grid trips is three days or so but I have done a few full week camping trips with no problems...

I call this NOT BAD for these three 12VDC 85AH GP24 Interstate Batteries I call my 255AH battery bank I installed on my OFF-ROAD POPUP trailer in late 2008...

Roy's Image

Works good for me...

Roy Ken

I've seen lots of new Trojans holding 12.7 volts but at 90-92% state of charge.

Some forms of logic insist a person speed up so they get to a gas station before they run out.

But as long as people asssssssssssume voltage means state of charge, this type of question will keep resurfacing. It's like saying "There's 13 lbs of pressure in the radiator - it CAN'T Be Low On Water!

Your new T-105s should have been fully charged at 14.8v from a deep cycle and then overcharged as required to get their SG right up to spec before starting the test. Just being at 12.75 is not enough evidence of being full after first getting them home new.

The inverter causing unusually low voltage for the same amps as before could be a sign of that. Or you have a wiring issue with the new installation adding to the R the inverter sees.

The 20 hr rate on a pair of T-105s is 11.25 amps (225/20) so 10 is not enough for this test. You do need the hydrometer to know when you are near 50% (which can come early if they are not at 225AH--eg they can be sulfated or just in the cold. At 45F they would be down about 10% to 202AH approx.)

Of course if they are in the cold and at 202 then now your 10a is about right. I stay with the 11.25 and adjust the AH results for temp afterwards. Not too sure how you are supposed to deal with that properly.

The 11.9v seen after a time is the loaded voltage so you have to wait a bit after removing the load when your hydrometer says they are at 50% (1.175ish ) to see what voltage they bounce back to. Should get to 12.1ish within an hour. Don't expect perfect line up between the SG and bounce back voltage for the 50% marker. If you have an AH counter that also helps. You have to get then all close enough and just "declare victory."

Don't forget temperature!!! If it is 50F instead of 80F your spec hydrometer SG will be higher, your voltages lower, and the adjusted correct capacity will be lower too.

IE, your 50% SG marker will be higher than 1.172, your bounce back voltage will be under 12.1, and your time will be less than 10 hours for under 225 and it will all be good as. Temperature!!!!

That is a timed capacity test, to see how much you can draw out
Aka how many ampHrs the battery has
A load test uses a much higher amp draw for 15 seconds and the voltage has to stay in the green on the load tester
In your case perhaps 100 amps
Your coffee maker will draw any where from 700w aka 60 amps single cup brewer, to 1500w 130 amps for a full size kurige
Our under cabinet drip maker is 900+ watts

Are you trying to brew coffee from full charge or after the capacity test

Trying to brew coffee from at or below the 50 percent SOC
Seems like a bad idea to me

Why not charge to full, do a normal night of tv etc..
And then check voltage and brew coffee in the morning

Check all cables especially chassis ground, remove clean re-tighten

You could try a non calibrated load test, by brewing coffee with fully charged batteries