Experts please critique my analysis/handling of electrical problem.

[nicholsong]

SCENARIO

Several relations visiting, MH chosen for our own 'spare bedroom'. First evening Truma blown air heating turned on pre-supper. All OK. Second evening Truma on 2000, charger on EHU working.

PROBLEM

About 2300+ return to MH, 2x85Ah L/A batteries down from 12.6v to 11v. EHU had disconnected.

ANALYSIS

I started first with EHU supply. Changed cable EHU supply and battery charging restored, RCDs not tripped, so that disconnection was separate IMO.

What damage to batteries at 11v?

I left batteries on charge for 48 hours with no load. Then left them at rest for 2 hours to dissipate residual charge on plates. Voltage read 12.6v at control panel (even with new batteries never reads more at panel and usually 0.1v higher at terminals.)

Next test is to load batteries. Most lights on, but not Truma fan in case fault is there. Load showing 2.5A discharge, maintained for 6 hours.

Left batteries at rest to recover for 12 hours. Batteries then show 12.4v., after 3 days they are down to 12.3v with no charge (EHU nor Solar)

QUESTIONS

1. Is it likely that the Truma fan without EHU charging could have drained the batteries from 12.6v to 11v in 3.5 hours? Should I be looking for another original problem, e.g. Truma fan motor?

2. Was a load of 2.5A for 6 hours sufficient to test whether there is permanent damage to the batteries or should I load them for longer and how long?

3. According to answers to above Qs my next test would be to activate the Truma heating and observe the discharge. The fuse had not blown so presumable not a dead short, but maybe a mechanical fault(bearing?) causing a higher drain on the batteries?

4. Is my analysis logic and testing correct so far?

I would welcome expert opinion and advice please, not speculation.

Geoff

 

[scotzsue]

No idea Geoff hope some suitably knowledgeable person comes along who can help.

 

[TheBig1]

What is the age and condition of the batteries Geoff? 2.5a continuous draw for 6 hours is15ah. If the batteries are weak, they look like they are charged but the capacity in ah is greatly diminished. 11v briefly is not terminal unless done too often or left at that state of charge. If you have access to a maintenance repair charger, use it occasionally to desulphate the lead plates

 

[Jimbohorlicks]

Just put them on a seperate battery charger for 12 hours plus and then see what they are like .

 

[nicholsong]

What is the age and condition of the batteries Geoff? 2.5a continuous draw for 6 hours is15ah. If the batteries are weak, they look like they are charged but the capacity in ah is greatly diminished. 11v briefly is not terminal unless done too often or left at that state of charge. If you have access to a maintenance repair charger, use it occasionally to desulphate the lead plates

Sorry, I should have included info that batteries are 2 1/2 years old and are kept well charged by EHU at home and B2B on road.

Discharge of 2.5A is the max I can load them at as we do not have much load other than lights. To really check that I will not get a failure when travelling should I load them for longer than 6 hours?

It is a pity that drop testers have been banned by H&S.

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[AdrianChen]

Not an "expert" so please ignore......

How old are the batteries? They loose capacity naturally every year.
Are they Flooded,AGM or Gel? I've assumed flooded.

1. If the batts capacity is 170amps, and it was all gone with just that load and no charge source it was running at 48 amps. Too high for a fan on its own.
2. The test removed 15AH from the batteries the final voltage recorded of 12.4v equates to roughly 80% of capacity, so roughly 20% of batt capcity used. 20% of 170AH = 34AH, so decline is double (56%) what might be expected. Batts possibly 95.2AH capacity.
To test - Separate the batteries and test them individually at 4.25a/C20 (one may be worse), and use an accurate multimeter (with a good battery installed in it) for measurements. 4 hours would give a very clear result (especially if they are down to 50% capacity), but with the meter just log the voltage every hour, stop at 50% (12.07v) and allow time to settle check rested voltage and do the maths.
3. Testing the Truma fan amps draw is fine, and may help as there may be a fault or wiring issue, but at that discharge I would expect fan fuse to blow so the batteries capacity seems to be at the root of it from the numbers you have quoted.
4. Logic fine. I would complete a better capacity test of the batteries, and from that understand their true capacity, which will include any permanent damage that may have been caused recently.

 

[Lenny HB]

It is a pity that drop testers have been banned by H&S.

That would have been useless for testing a leisure battery, they are for starter batteries.

Sounds to me like one or both batteries have had it, when charging them they should have got up to 14.2 - 14.4v and after resting still be over 12.9v
If one battery is faulty it will drag the other one down with it, best to seperate the batteries and test each one with a slow discharge

 

[TheBig1]

As above test the batteries separately on a controlled discharged, measuring state of charge every hour. It does sound like one or both are now bad. I know people think leaving batteries on charge prevents them going bad, but especially with a dumb charger, the opposite is true

 

[AdrianChen]

Sorry, I should have included info that batteries are 2 1/2 years old and are kept well charged by EHU at home and B2B on road.

Discharge of 2.5A is the max I can load them at as we do not have much load other than lights. To really check that I will not get a failure when travelling should I load them for longer than 6 hours?

It is a pity that drop testers have been banned by H&S.

Please do say if they are AGM/Gel/Flooded. AGM would be much higher resting voltage 12.8, standard chemistry flooded 12.6.

 

[nicholsong]

Please do say if they are AGM/Gel/Flooded. AGM would be much higher resting voltage 12.8, standard chemistry flooded 12.6.

I said L/A (Lead/Acid) in my OP.

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[funflair]

I said L/A (Lead/Acid) in my OP.

AGM and Gel are both still under the Lead Acid heading Geoff, I guess you mean yours are "Flooded Lead Acid"

 

[nicholsong]

AGM and Gel are both still under the Lead Acid heading Geoff, I guess you mean yours are "Flooded Lead Acid"

Yes Martin.

Does it make much difference to the problem and analysis?

 

[AdrianChen]

Yes Martin.

Does it make much difference to the problem?

No, but it might help with further assistance following more tests, and being young batteries it may help to be sure what type.

Didn't mean to be a pain

Sorry

 

[funflair]

Yes Martin.

Does it make much difference to the problem and analysis?

Only to the diagnostic process I think as the different types have different resting voltages, as has been suggested it might be worth pulling them off the van and testing each one separately.

 

[DBK]

Is it possible you misread whether the EHU was working as you describe in your first paragraph? If it wasn't working the batteries may have been already well discharged at the outset. The best way to test would be to reproduce what you did, running the Truma fan but perhaps only for a couple of hours after starting with fully charged batteries and without EHU. If the battery voltage drops to anything like 12 volts after just a few hours of use it sounds, as Lenny suggests like a goosed battery or two.

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