Battery Testing Help re: Figures (1 Viewer)

[Emmit]

Hi All,

Finally received my digital Multimeter through the post so now have the necessary to check (Confirm actually) that the Batteries in the 'van are FUBAR.
This is what I have;
2 x 110volt leisures wired in parallel.
2 x 55 watt headlamp bulbs wired in series for test lamps

So I have 220Ah of Batteries and 110watts of bulbs which equates to 9.1 Amps.

I intend to put the bulbs on for 6hrs by which time I should have used 55Amps of juice which is a quarter of the available output of the batteries.

The starting voltage of the batteries was 12.63 which I know is a sign the batteries are beyond redemption before I've started.

Other than that, are my calculations correct?

Thanks in advance

 

[Poohbear]

12.6V is perfect for a start point and indicates a healthy battery

 

[funflair]

Well your batteries are ah not volts, but you knew that.

Your bulb/bulbs will be connected each one straight to the battery/batteries so 9 ish amps looks OK.

I would be tempted to separate the batteries and possibly just run one bulb each battery so then 10 hours (45ah) your battery should still be above 12volts.

Martin

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[tonyidle]

Your calculations are correct ........... ish. Battery capacity in Ah used to be quoted in relation to a standard which was the "20 hour rate". What this means is a fully charged 100Ah battery discharged at 5A (100 / 20 = 5) could be expected to last for 20 hours before being fully discharged. Unfortunately lead-acid batteries don't conform to a linear discharge relationship so the same battery would not take 10 hours to discharge if the load applied drew 10 amps - it would actually last for less than 10 hours. All that is bad enough but battery manufacturers do not all quote at the "20 hour rate" - to make their batteries appear to be of higher capacity they might quote capacity at a 30 hour rate. Or more likely dream up a capacity that suits the appearance of the battery.

Voltages: you will find tables published that relate volts to state of charge. The measurements must be taken after the battery has been totally disconnected from either the charger or any load for at least one hour. Temperature also influences the readings. The battery must be fully charged for the test which, with a smart charger, may take more than 20 hours per 100 Ah capacity. Without a smart charger it may never happen.

 

[pyro]

Am I going mad here?

Surely the two bulbs should be wired in parallel, not in series, to get the required current drain?

If you wire them in series, you double the resistance, halve the current

 

[Emmit]

Funflair wins the Grand prize for noting my deliberate mistake
That's a week for two chasing the pigeons off my veggies when I go on my hols.
Second prize is two weeks doing the same

Thank you for your suggestion as to testing the batteries separately. May do that as the batteries were not a matched pair and it would be good,(if they pass the first test) to see the relative performance of each one.

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[pyro]

Funflair wins the Grand prize for noting my deliberate mistake
That's a week for two chasing the pigeons off my veggies when I go on my hols.
Second prize is two weeks doing the same

Thank you for your suggestion as to testing the batteries separately. May do that as the batteries were not a matched pair and it would be good,(if they pass the first test) to see the relative performance of each one.

In other words the bulbs should be run in parallel. I'll pass on the second prize

 

[funflair]

Am I going mad here?

Surely the two bulbs should be wired in parallel, not in series, to get the required current drain?

If you wire them in series, you double the resistance, halve the current

You see I bottled out of the theory and opted for separating the batteries and a bulb on each so no confusion

But that was my interpretation of V=IR

Martin

 

[Emmit]

Plan C now in operation.

Replacing anything I've lost in the above c*ck up by plugging in the EHU.
Will go back to the 'van tonight and after giving the batteries an hours rest from EHU, test the batteries one by one overnight using one bulb only as per @funflair suggestion.

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[denisejoe]

You are assuming you have 220 amps of power but I think you'll actually only be able to use 110 before the batteries are knackered.

Joe

 

[Emmit]

You are assuming you have 220 amps of power but I think you'll actually only be able to use 110 before the batteries are knackered.

Joe

Thanks for that Joe but I was aware that I couldn't go below half of the 'Headline ' Amps. The 220amps is purely for the purpose of the test.

 

[Emmit]

Update on this.

Today I divided the batteries and attached a 55watt bulb to one of them.
I left it on for 6hrs which I calculate at about 27amps worth (approximately 25% of 110 Amp capacity)

I'm left with a battery showing 10.55 volts.

Can I assume the battery (and therefore it's mate of three years) is dead, kaput, FUBAR'ed.

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[funflair]

I think the one you tested is certainly suspect/fubar, if you fancy saving the other one if possible test it the same but if the result is the same "It's dead Jim" ok your not Jim but hey ho, out of interest are these sealed batteries or open and if open have you checked electrolyte level?

What batteries are they and have they been left flat?

Martin

 

[Emmit]

Just for the info.
The older of the two batteries was six years old having migrated from our days as a tugger.
The second battery is now over three years ago having been put in by the selling dealer when we bought the van.
Both of them are nondescript and I have no complaints.

The older one had a pretty hard life before it went into the van and has dragged the 'newer' one down. On another thread I have discovered that the charger fitted to the 'van has been out of action for apparently a long time and the batteries have been fed soley by the solar on the roof.

Now that the charger is up and running I don't expect the same scenario once I replace the batteries.

I have in mind to fit 2 x 120Ah AGM's which I am led to believe, will give me more depth of use than 'Wet cell'

 

[funflair]

Just for the info.
The older of the two batteries was six years old having migrated from our days as a tugger.
The second battery is now over three years ago having been put in by the selling dealer when we bought the van.
Both of them are nondescript and I have no complaints.

The older one had a pretty hard life before it went into the van and has dragged the 'newer' one down. On another thread I have discovered that the charger fitted to the 'van has been out of action for apparently a long time and the batteries have been fed soley by the solar on the roof.

Now that the charger is up and running I don't expect the same scenario once I replace the batteries.

I have in mind to fit 2 x 120Ah AGM's which I am led to believe, will give me more depth of use than 'Wet cell'

Can your charger handle AGM's? there are certainly people on here who don't like AGM's and I don't see the place for them a motorhome personally, we have GEL and think they are great but that's just based on the service they have given and still give us, if I wasn't using GEL I would go for good quality deep cycle Flooded lead acid.

Agree though the old ones don't owe you much.

Martin

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[Emmit]

Thanks for thinking about us Martin.

When I sent my duff charger off to the repairers I specifically asked the question re putting in AGM's and I had a conversation with 'the man' .
He stated categorically that the charger in our van was not only up to the job but that AGM's in the 'van would be fine.