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2x100AH lead acid leisure batteries 3 years old. Assuming 80AH usable in total.
CTEK D250s, 120W solar, 20AH engine charger
NASA BM1 Battery monitor
All cables well spec'd (over spec'd) - negligible voltage drop in all scenarios.
All fuses/connections good.
Assume almost zero solar input for the example.
Compressor fridge @ 2.5A when running, 1/3 of the time, max, say 25AH per day
Diesel heating, 20A startup for 2 mins, (pulsed, so shows 10A). 1A when running
Lights (LED), pump, and other bits negligible.
I make that as the fridge should run for 3 days (72H), and the heating for a few hours a day quite easily.
At the Hereford meet, the LBs were fully charged (from driving/solar, but also put on hookup before we left and the 240v smart charger agreed and did nothing!)
Arrived at 16:00 Saturday, but by 08:00 Monday the fridge stopped working for the first time ever, and battery voltage looking a bit low. That's 40hrs - and far below expectation and past experience.
Put the heating on and the voltage went <11v for a few seconds and as expected everything shut down. So appears batteries were dead.
On Monday afternoon we started the van engine for 30 mins, @ 20AH charge, and hence put 10AH back into the battery. During this time, the heating was on and running. We didn't put the fridge back on, but did use lights, pump, charge phone etc - with no flickering of lights. Then, even with this slight top up, the heating worked quite happily a couple of times thereafter with no slowing of fan or issues during high current startup-shutdown. Normal voltage behaviour.
The fridge is pulling the correct current (easily seen on BM1) and ran happily for a short duration post engine run, but we left it off as beer was cold enough
Odd.
Driving home, 2hrs, 40Ah max back into battery, and NASA BM1 reading fully charged, and the ctek was just dribbling in 6A by the time we parked on the drive.
Now - I'm 100% happy the CTEK is working perfectly, and is putting in 20A when driving (unless batteries full). Alternative smart charger agrees with CTEK when batteries are full.
Odder.
So - question is, how can 2x100AH batteries die, then work well after a minimum top up, and then be full with only a small charge applied that shouldn't have filled them up?
Have them out now under individual load testing to see if either has failed, or if its just an old age thing, or if something weird went on that caused the voltage to drop massively before its time?
Notes:-
* Batteries removed, both at 13.3v after 15 minutes away from power
* Load test is running a 240v halogen 20W light via a naff inverter, best I can knock up to be consistent.
* Batteries tested individually with same results, suggesting one battery hasn't failed.
* Batteries drop to 12.9v within 30 seconds
* After 40 minutes, batteries at 12.38v
Currently running longer duration load test on 2x50W halogens via inverter (9A or so draw)
I was expecting one obviously duff battery, but appears not.
(EDIT TO ADD: The BM1 reported batteries as flat <5%, and after 30 min engine, 17%. But overnight (with no extra charging) went up to 90% - so not sure the BM1 is overly trustworthy!)
Thoughts?!
CTEK D250s, 120W solar, 20AH engine charger
NASA BM1 Battery monitor
All cables well spec'd (over spec'd) - negligible voltage drop in all scenarios.
All fuses/connections good.
Assume almost zero solar input for the example.
Compressor fridge @ 2.5A when running, 1/3 of the time, max, say 25AH per day
Diesel heating, 20A startup for 2 mins, (pulsed, so shows 10A). 1A when running
Lights (LED), pump, and other bits negligible.
I make that as the fridge should run for 3 days (72H), and the heating for a few hours a day quite easily.
At the Hereford meet, the LBs were fully charged (from driving/solar, but also put on hookup before we left and the 240v smart charger agreed and did nothing!)
Arrived at 16:00 Saturday, but by 08:00 Monday the fridge stopped working for the first time ever, and battery voltage looking a bit low. That's 40hrs - and far below expectation and past experience.
Put the heating on and the voltage went <11v for a few seconds and as expected everything shut down. So appears batteries were dead.
On Monday afternoon we started the van engine for 30 mins, @ 20AH charge, and hence put 10AH back into the battery. During this time, the heating was on and running. We didn't put the fridge back on, but did use lights, pump, charge phone etc - with no flickering of lights. Then, even with this slight top up, the heating worked quite happily a couple of times thereafter with no slowing of fan or issues during high current startup-shutdown. Normal voltage behaviour.
The fridge is pulling the correct current (easily seen on BM1) and ran happily for a short duration post engine run, but we left it off as beer was cold enough
Odd.
Driving home, 2hrs, 40Ah max back into battery, and NASA BM1 reading fully charged, and the ctek was just dribbling in 6A by the time we parked on the drive.
Now - I'm 100% happy the CTEK is working perfectly, and is putting in 20A when driving (unless batteries full). Alternative smart charger agrees with CTEK when batteries are full.
Odder.
So - question is, how can 2x100AH batteries die, then work well after a minimum top up, and then be full with only a small charge applied that shouldn't have filled them up?
Have them out now under individual load testing to see if either has failed, or if its just an old age thing, or if something weird went on that caused the voltage to drop massively before its time?
Notes:-
* Batteries removed, both at 13.3v after 15 minutes away from power
* Load test is running a 240v halogen 20W light via a naff inverter, best I can knock up to be consistent.
* Batteries tested individually with same results, suggesting one battery hasn't failed.
* Batteries drop to 12.9v within 30 seconds
* After 40 minutes, batteries at 12.38v
Currently running longer duration load test on 2x50W halogens via inverter (9A or so draw)
I was expecting one obviously duff battery, but appears not.
(EDIT TO ADD: The BM1 reported batteries as flat <5%, and after 30 min engine, 17%. But overnight (with no extra charging) went up to 90% - so not sure the BM1 is overly trustworthy!)
Thoughts?!
Last edited:
But I did expect an instant obvious failure, as we can't explain some of the behaviour.
