Electrics - Battery goes flat too quickly

[Shaun_E]

I have a major problem in that the battery on my car goes flat after 2 days without a conditioner. this obviously precludes going away for a weekend ☹️.

The battery is a Red Top 15 purchased new in April and should have ample storage capability to last a few days even with the immobiliser on. It has now been almost completely discharged 3 times due to not having the conditioner available so I hope I haven't damaged it.

 

The question is where do I start in looking for the cause of the drain and how do I find/measure it? I have had a few electrical issues during the rebuild including a broken dip switch, fried headlight switch, reversing light blowing the fuse. I have disconnected the live to the reversing light (pending a propoer re-wire). What are the most likely causes of a short circuit?

 

This has to be my worst nightmare - I hate car electrics .

 

Yellow SL #32

[stevefoster]

Connect an ammeter in series. A 10A one should do.

You can do this without breaking power if you connect up first either side then remove the terminal from the batt.

This will tell you if there is something draining a lot but not what.

Have you charged the battery properly after it was flat? A trickle charger will never do it... nor will a drive and then leaving the car again. Verify the alternator by measuring the voltage across the battery, before, during and after starting / reving. You should have approx 12.8V then ~10V whiel cranking then ~14V running

A short should blow a fuse. You have a drain or a not properly charged or a duff battery by the sounds of it.

 

Be warned you should not really charge a gel cell for longer than a couple of hours on a normal batt charger or really leave a trickle charger conntected that is not specifically ment to these types of batts. There is lots on the archive discussing this.

 

I have the same batt and can leave it a long time and its still fully charged. I don't have an immobiliser and always switch off the batt cutout after any run.

The battery could of course be faulty...

 

Fried headlight switch? What caused this?

 

Good luck and let us know how you get on.

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

[Shaun_E]

Cheers Steve.

I have an ammeter so will check the drain. The battery was recharged with a Halfords intelligent (if that isn't a contradiction ) charger that works as a normal battery charger until the battery is charged and then switches to a conditioning mode. The alternator is fine - I get about 14.2 V when running (the Stack has a voltmeter on it) but I can't remember checking the voltage when not running so will double check that.

The fried headlight switch was my mistake when trying to find the dip switch problem - the headlight switch is very close to the big red starter button and when I was taking the switch out managed to touch the two together briefly 😳.

The problem is almost certainly a drain somewhere - my first suspect was my additional power sockets for bullet cam, etc as my soldering isn't the greatest but I've checked and there are no short circuits on any of the additional sockets I put in. I had problems with the reversing light blowing the fuse (also the brake light fuse!) as it is the old wiring with a permanent live feed to the light and earthed through the switch but this feed is switched through the ignition so shouldn'tbe a problem - I have disconnected it anyway but it wasn't the problem.

I was hoping that someone might have some ideas as to the type of thing that might be causing a significant current drain so that I could check them first, otherwise it's going to be one of those nightmare processes of elimination ☹️.

 

Yellow SL #32

[old captain slow]

I hate to be a gloom and doom merchant but if you have discharged the battery to "flat" it will be knackered I'm afraid. ☹️

 

C7 CDW

[stevefoster]

In theory to flatten the Redtop 15 in 2 days (13AH I believe it is) you only need 0.27 Amp / hr.

That's 3.24W. Enough to run a small interior bulb, a half bright sidelamp or a very dimly glowing brake light.

Just examples but it gives you an idea.

 

Hants (North) and Berkshire Area club site here

My racing info site

here

 

 

 

[Shaun_E]

Have just spoken to DMS and if I have completely discharged the battery then it could well be knackered - I might be lucky and just suffer a slight reduction in capacity but otherwise it's new battery time ☹️

 

Yellow SL #32

[Shaun_E]

Measuring with a cheap ammeter (i.e. not that accurate) the current draw is about 12 mA. The battery voltage is 12.8V - will check that again in a couple of hours now that I have disconnected it and removed the conditioner - as long as it doesn't drop then the battery should be OK.

I have a thin wire connected to the battery earth which, if connnected on it's own (i.e. main earth strap not connected), makes the ECU live and triggers what I think is probably the IACV. Is this correct (may be a red herring)?

I think I need to get better ammeter before progressing.

What should I start unplugging to see if it is the cause of the current drain? There can't be much that doesn't go through the ignition switch.

 

Yellow SL #32

[Shaun_E]

I connected the ammeter in series and then pulled each fuse in order - none made a difference. I then pulled the flasher unit out and replaced it as I have had a dodgy connection with it. I then tried the hazards which worked fine but since then the current drain has gone off the scale (only 250mA meter). Have pulled each fuse in turn again and still makes no difference.

If I understand this correctly the problem must therefore be on the battery side of the fuse box. What can I check or unplug to find the cause? I'm really struggling now.

 

The only slightly good news is that the battery is still reading 12.8V so I might have got away without completely destroying it.

 

Yellow SL #32

[Bob Corb]

Shaun

 

I dont suppose you have a roller barrel converted VHPD or similar (MBE management)? My car also discharges the battery very quickly. When I connect the battery master switch I get a click from the MFRU which I think is connecting the heater for the lambda sensor? I keep meaning to sort it. I've found out that R400s dont even use the Lambda sensor so I've taken it out and put a plug in the exhaust hole. I still get the click though which means the relay is still pulling in.

 

Try disconnecting the MFRU or the ECU and see what happens, if the power drain goes away your onto something. My new engine loom which I fitted with the roller barrels was totally screwed up. There was no power feed to the fuel pump relay and this bizarre click was puzzling me. Caterham fixed the fuel pump feed but drew a blank on the click...I'm hopefully going to have a nosey around an R500 soon so I'll compare the wiring of the ECU and MFRU pin for pin...

 

Bob

[Shaun_E]

Cheers Bob,

Don't have an MBE but that is something else for me to try. Will unplug the ECU and the MFRU and see what happens. At the end of my tether on this and will very shortly be looking for a professional to fix it for me.

Anyone know what the best route would be - an auto electrician or a Caterham service agent? Any recommendations in Berkshire/Thames Valley area?

 

Yellow SL #32

[LazerBrain]

Shaun,

 

I found that the ECU takes about 0.5A until it goes into standby mode when it drops to around 10-20mA (same as your measurement.) I think the time it takes to drop to standby is 10-15mins.

 

As you saw large current consumption when you had the hazards flashing, and the hazard switch is a known problem you could consider removing all the fuses except for the hazard circuit. Were the indicators on when you saw the >250mA reading?

 

Be careful about using a meter with a low current range when you are expecting higher currents. You might pop a fuse in the meter, or damage the meter.

 

cheers,

 

Darren.

[Shaun_E]

Right - I've got myself a decent multimeter and can now say that the current draw is about 13.5 mA which doesn't seem that much. Reading some of the other posts on this subject, a draw of 40mA would not be unusual so mine is quite low. Either there is another current draw I'm not aware of (intermittent?) or my battery really is knackered. The RedTop 15 has a capacity of 14Ah so should give 1000 hours before going flat with the above current draw. Could it be that the ECU is taking much longer to go into standby mode, by which time the battery is nearly drained? I think I can test this.

 

The battery voltage when everything connected back up is 12.89 volts which sounds good to me - it's been disconnected overnight. When charged it has no problem starting the car and after 24 hours it can still start the car easily. Is there perhaps another problem and the battery isn't flat at all? This doesn't make much sense to me at the moment.

 

Yellow SL #32