Force 30 A/H Charge or Diagnose the problem?

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The Laird
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Joined: Thursday, July 30, 2009 - 00:47
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Force 30 A/H Charge or Diagnose the problem?

Hello Folks,

I have noticed that one or two people have intimated that they are willing to use the 'force 30 A/H charge' which is available via the Vectrix diagnostic software.

I have no wish to tell anyone what to do BUT, it may not be a good idea to use this facility.

Consider this. The battery is your 'fuel tank'. It can hold, at best, 30 ampere hour. If it is not accepting 30 A/H under normal charge conditions OR if it it not providing 30 ampere hour after being charged, then there is a 'fuel tank' problem.

Forcing 30 ampere hour into a 'fuel tank' capable of holding less (due to the fault condition) is going to do damage. Far better to locate the cause of the problem than to force charge the battery. Just because Vecrtix have given us a means of forcing 30 a/h into the battery, it doesn't necessarily follow that we have to be dumb enough to use it.

Diagnosing a faulty battery is not that difficult. There are four things to check.

Capacity. Does each cell hold the same (30 A/H) amount of charge? If not, then do they all hold the same (or near abouts) charge as each other? Discharge the battery and then re-charge the battery at a know current. Measure the time taken to reach 1.45 volts per cell BUT DO NOT allow any cell to exceed 1.45 volts.. Multiply the time (in hours) by the current (in amperes). This is the battery capacity in ampere hours, if the result is greater than 24 ampere hour then the battery is fit for further service as it has 80% or more of it's original capacity.

Internal resistance / impedance
. Has each and every cell got the same internal resistance?

The cell resistance is quoted by 'Gold Peak' as being less than 1.2 milliohms per cell or alternatively 0.0012 Ohms per cell. To measure the internal resistance all that is required is a digital meter having four digit (a 1 and three 0's - sometimes known as a three and a half digit readout) readout and a scale of 2.000 volts. And a suitable load resistor such as a 12 volt 55 watt motor car headlight bulb.

Take a block of (say) nine cells. Measure the voltage of each cell using the 2.000 volt scale of the meter. Connect the 'load' (the car headlight bulb) and again measure the voltage of each cell. Subtract the second voltage from the first (for each cell). Measure the current draw by the load.

Now divide the voltage (the one obtained by subtracting the second reading from the first, two steps ago) by the current drawn by the load (the car headlight bulb) The resulting decimal figure is the resistance of the cell in ohms. They should be within 10% of the quoted 1.2 MilliOhms. If they are all the same as each other that too is acceptable. As long as they are less than 3.0 MilliOhms the battery should remain serviceable.

Open circuit voltage when charged. Are all cells the same voltage as each other? (Use a three digit meter for this measurement) The voltages should at least be within 0.01 volts of each other. Ideally, to get best results allow the battery to stand overnight before making this measurement Or discharge it for half an hour with that motor car headlight bulb.

Look for bulged cells. this is the easiest of all checks, the ends of the cell - the side of the cell groups - should be dead flat. Any bulging indicates 'overcharge damage'. the cell might still be in reasonable condition however and still serviceable. Excessive bulging usually denotes a cell unfit for further service.

I didn't say that these are all easy checks to make but they are the ones that will indicate serviceable / unserviceable cells / batteries.

Keep smiling, it can only get easier,

The Laird

Mik
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Joined: Tuesday, December 11, 2007 - 15:27
Points: 3739
Re: Force 30 A/H Charge or Diagnose the problem?

Great post, thank you for that!

One test that can add valuable insight would be a self-discharge test: Charge entire battery (or all cells of segments in quick succession) and let all parts stand for several weeks under identical temperature conditions. Then, test the remaining capacity by discharging the battery.

I've added this to the Collaborative Handbook, so please stay on topic.

This information may be used entirely at your own risk.

There is always a way if there is no other way!

X Vectrix
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Last seen: 3 months 1 week ago
Joined: Tuesday, August 4, 2009 - 05:20
Points: 298
Re: Force 30 A/H Charge or Diagnose the problem?

Or if you have access to that particular diag you could reset the capacity measuring routine and let the SW measure the available capacity. The catch is that if your batteries are in too bad of shape to accept a full charge you will have to set the gauge to full after charging in order for the routine to work. Or you could manually set the AmpHrs to something lower than 30.

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