Lotus Elan

How long to charge a battery?

PostPost by: Hongokongo » Sun Aug 24, 2014 4:56 pm

Wanted to go for a spin today. After three or four turns of the key the battery was flat (or appeared so) and so I put it on charge. After 15 minutes the car started as if the battery was new. Surely it should take longer to charge the battery, and I wonder what else it might be.
Any ideas?
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PostPost by: Chancer » Sun Aug 24, 2014 8:11 pm

Its the heating effect of putting it on charge that temporarily lowers the internal resistance releasing more power.

You can do the same thing with a flat bettery on a cold day by carefully pouring a kettle of boiling water on it.

Taking the battery in the warm and charging it for 15 minutes will usually start a car that would not even crank in cold weather.
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PostPost by: StressCraxx » Sun Aug 24, 2014 9:15 pm

Sometimes an older battery will deteriorate due to sulfidation or loss of electrolyte and only take a "surface charge". First, check the integrity of your chassis grounds(earths) and battery connections.

If you suspect the battery is bad, take it in to a trusted shop to have it load tested.
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PostPost by: AHM » Sun Aug 24, 2014 9:41 pm

It did all of the work getting fuel in the right places the first four times - so it didn't have to do much and 15 minutes was enough to recover.
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PostPost by: bob_rich » Mon Aug 25, 2014 10:17 am

Hi

If the engine is in good condition then only a small part of the battery's total capacity is required to start the car. 15 minutes of charging could easily be enough to get enough cranking power to start the car -- but it may not be anywhere near full charge the warming during the small charging will also help.

why did the battery only crank for 4 attempts? Check charging is OK. and or battery is in good condition. If you have a volt meter check the drop at the battery terminals when you switch on say the headlights should around 0.3V without engine running. If you car is standing for a long time is there a drain on the battery? or is the battery a bit old and its charge is leaking away internally

hope this helps best of luck

Bob
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PostPost by: denicholls2 » Mon Aug 25, 2014 2:03 pm

What the posters above didn't state is that if your battery was charged for only 15 minutes from flat, it's still almost flat. And in this state will deteriorate much more rapidly than it would when charged. Lead-acid batteries do not like storage in the discharged condition.

The battery is charged when the ammeter says it is (current stops flowing to it from the generator/alternator). This is the value of an ammeter over an idiot light.
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PostPost by: Hongokongo » Tue Sep 16, 2014 6:34 pm

Hi, an update, but I am a real novice with car electrics. The battery shows just under 12 volts when not used, but drops to about 6 when under load, so needs to be recharged.
Also, when the engine is idling, the ammeter is just in negative, and when driving with no lights etc on, just slightly in positive.
Is it the battery, or could it be the alternator, or even the ammeter.? Both are fairly new, but unused.
Thanks
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PostPost by: billwill » Tue Sep 16, 2014 6:58 pm

When running normally above idle, the ammeter should indeed show only a small + current, but just after starting the engine there should be a significant + current for 2 or three minutes as it replaces the power used during starting.


But a battery showing only 6 volts on load indicates that you are doing a massive overload or the battery is worn out.

It depends a bit on where you measured it, but if that was direct from the battery terminals it is pretty certainly dying. However if it was from one terminal to chassis or elsewhere in the car, you may just have bad earthing connections.

Under full starter motor power with a good battery it may drop to about 9 volts output.
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PostPost by: Hongokongo » Tue Sep 16, 2014 7:48 pm

Thanks Bill,
The battery is 4 years old, but the car has only done 2500 miles in that time. I assume it is the lack of use that has caused it to deteriorate. I tested it across the terminals, a new battery I suspect.
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PostPost by: billwill » Wed Sep 17, 2014 1:06 am

It's long periods with the car unused that most often ruins batteries.

I've lost several that way.
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PostPost by: fasterbyelan » Wed Sep 17, 2014 10:51 am

Hongokongo wrote:Thanks Bill,
The battery is 4 years old, but the car has only done 2500 miles in that time. I assume it is the lack of use that has caused it to deteriorate. I tested it across the terminals, a new battery I suspect.



Almost certainly the reason, they just don't store well.

I gave up replacing my battery after the 3 failure whilst my Elan was stored. I now use a Varley Red Top battery (VRT 40) ,which does not suffer from this problem (I get them for free with very little use on them). I hope to be able to install this type properly when I finish my restoration.
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PostPost by: Plus 2 » Wed Sep 17, 2014 3:15 pm

If storing the car for long periods and you can get close to a power supply then invest in a battery conditioner.

I have got the CTEK conditioners (not trickle chargers) on all my cars and they have already paid for themselves and it ensures the car starts when you want it to.

If a standard car battery is allowed to fully discharge it can not be charged back to its full capacity. I used to be responsible for maintaining over 300 engineering prototypes and was always receiving 'lectures' from the Battery Engineers (usually Doctorates in physics) on why the batteries had to always be kept charged.

All the best

Steve
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