Low battery

[robb4100]

Hi all,

Tried to start the car (S2 elan)last night and ignition light was on, fuel pump working etc. Tried to crank the engine but was unable to generate enough power to turn it over.

This AM checked the voltage (11.7), ran a set of jumper cables to the car from my jeep and it started right up. I removed the jumpers and after a couple of minutes I shut the engine and re-started without the jump. I gather from this I had enough juice to start a warm enging but not enought to turn over the cold one. I currentlu have the battery on a charger.

I want to get to the root cause of this.

Some driving history for this year.
Replaced the front harness this winter. Battery was out of the vehicle all winter, plenty of power to start the car after the harness job was done. I drive 1-3 days per week for oughly 1/2 h twice on those days.

Voltage across battery at 1000 rpm is 11.7 should this be higher?
Is this likely a generator (has not been fitted for an alternator) issue?
i am about to dig out the workshop manual but would like to get your insight in parallel.

thanks

Robb

[MintSprint]

To be honest, I'd anticipate problems with that sort of usage (irregular/short trips) with a dynamo (generator). It will only be putting charge into the battery at higher revs and it is likely that starting the engine is draining almost as much juice as the dynamo will replenish in a half hour drive.

Voltage across battery at 1000rpm is not surprising, if the battery charge is a little low, since at these revs the dynamo probably won't be giving charge and current is being drawn from the battery to feed the ignition, etc.

It would be worth checking that the regulator is correctly adjusted, though, to control the maximum voltage and cut-in point on the dynamo. The workshop manual gives instructions how to do this, but if you can find an auto electrician with experience of old English cars, it would only take him ten minutes to check and adjust. It wouldn't do any harm to make sure all the terminals and connections are clean and tight, too, to minimise resistances.

Other than that, you probably need to think about keeping the car connected to a trickle charger when it's not in use, and/or convert to an alternator.

[elansprint]

Suggest you check the battery cable connections at battery & solenoid & solenoid to starter lead as well as engine earth. Check there is no broken strands. My starter motor lead had several broken strands replaced this & off she went the cable run is quite long from boot so when pulling 400 amps for starter the volt drop in the cable can be high unless in good condition. Get battery load tested could be battery past its best & as above would always connect a trickle charger will extend life of battery.
regards
Ian

[types26/36]

Tried to start the car (S2 elan)last night and ignition light was on, fuel pump working etc.
This AM checked the voltage (11.7),
Voltage across battery at 1000 rpm is 11.7 should this be higher?

A Fully charged battery should be 12.6volts, once it has dropped to 12v and under it is unlikely to start your car, measuring the voltage across the battery with the engine running the voltage should show an increase of voltage as the revs rise to a maxium of about 13.8V (depending on temp and battery state)
Even at 1000 rpm it should not be showing a discharge unless you have current consumers switched on (example lights)
The worst thing for a battery is not being used, a trickle charge and an occasional boost will prolong the battery life and the trend now is to use a battery conditioner.
As your battery had reached a low state of charge have it charged and then load tested as per other posts although if it is not chargeing at 1000rpm it sounds like you may have a generator/regulator problem.

[oldokie]

Meters can vary a bit, but I like to see 12.5 across the battery. If you can remove the caps, check that the 'burbling' is consistent in all the cells while on the charger, a short burst ( 10 min) @ 50 amps will often retard sulfation. Once the battery is fully charged a simple load test can be done with a multimeter, voltage drop with starter engaged should be less than 15%. Hope this helps.

[chicagojeff]

One good thing about having a battery cutoff switch installed is you can turn off the power when you park it, prolonging whatever battery life you DO have. Doesn't get at the root of your problem, but will help get you home more often.

[robb4100]

Thanks everyone as always the comments are great

This is what I can tell you so far.

measuring the voltage across the battery with the engine running the voltage should show an increase of voltage as the revs rise to a maxium of about 13.8V (depending on temp and battery state)

The voltage does not rise when the engine is revved. I will isolate the generator/dynamo and check to see if it is working.

I was able to get a full charge on the battery overnight so can run it and do some more diagnostics.

and the trend now is to use a battery conditioner.

I did a quick check online and most of the battery conditioners seem to be sold in the UK. Any recomendations for a US conditioner(want to avoid adapters)

Thanks!

[types26/36]

Sorry cant help with U.S. conditioners.
I am not sure which regulator you have, the later RB 340 three bobbin or the earlier RB 106 two bobbin, here are some links that may help you with your diagnostic but really you are wasting your time as the answer is to fit an alternator, "Lucas the Prince of darkness" takes no prisoners
http://www.ponypics.com/spitfire/regulator.html
http://www.mgoctagoncarclub.com/articles/regulation.htm

[oldokie]

You might try Northern Tool or The Battery Zone ( ads at bottom of this page) for a battery minder. Now, a stupid question, I have avoided fitting alternators all these years because mine are +earth( didn't want to change tachs, etc,), can I use an alternator without changing polarity?

[types26/36]

't want to change tachs, etc,), can I use an alternator without changing polarity?

The short answer is no but the Tach can be converted or a later Tach used. All other things will work on negitive earth but be aware if you have a radio it is ground sensitive.

[wojeepster]

You can buy a shumacher trickle smart charger at wally world for $17.44 It will sllllooooowwwlllllyyy charge your battery then go to float and keep it charged but not overcharged. It has a switch and you can carge 6 or 12v .

[RotoFlexible]

Now, a stupid question, I have avoided fitting alternators all these years because mine are +earth( didn't want to change tachs, etc,), can I use an alternator without changing polarity?

Fit the alternator, switch over the tach, and be happy. The dynamo just isn't up to the job unless everything is right up to snuff. The alternator will keep your battery fully charged while you are driving, even with the lights on at night (and by the way, they'll be brighter) - a bizarre concept for the Elan driver but there you are!

[oldokie]

Thanks guys, that's what I thought, I'm sure you're right about the lights. The H4's(90/130) do tax the system a bit!

[elansprint71]

Thanks guys, that's what I thought, I'm sure you're right about the lights. The H4's(90/130) do tax the system a bit!

130 watt main beams? I hope you upgraded your wiring and your fire extinguisher.

[robb4100]

Thanks everyone,

I have been working at a snails pace (too many competing priorities). Checked the Dynamo and it topped out at about 3 volts so it needs to be replaced.

Question: Why would I not switch to an alternator? The car is not original (cobbled together from 3 elans- frame; body; engine) so it is not a show car.

Thanks