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        General >> Problems >> Cosworth Battery Draining
        
(Message started by: KeithCEng on Jun 26^th, 2015, 8:10pm)

Title: Cosworth Battery Draining
Post by KeithCEng on Jun 26^th, 2015, 8:10pm

Evening all,

My battery has been draining overnight on several occasions so I started investigating in detail. Using a "Clamp" Ammeter, I proved that the Alternator was working properly, putting 18A into the Battery on tickover; I turned off the ignition and radio and closed all the doors - the only thing open was the Bonnet (Alarm system OFF) and using the same Clamp Ammeter, I measured a drain of 0.6A from the Battery - I then removed and replaced fuses (one at a time) from the Central Fuse box to see if one was associated with the drain – made no difference - still had 0.6A drain. I then did a similar exercise with the fuses in the Auxiliary Fuse Box – made no difference! I then removed Relays R16, R17, R19, R21, R24 one at a time from this box – again made no difference. Went back to the Central Fuse Box and removed Relays R2, R3, R4, R5 in turn – made no difference!(I was unable to access the remaining Relays at the rear of this box).

I believe that PATS should only take about 0.1A? It seems that whatever is causing the drain is not routed via the Fuse Boxes.

Does anyone have any thoughts on this?

KeithCEng

Title: Re: Cosworth Battery Draining
Post by Andycan on Jun 26^th, 2015, 11:32pm

A common drain is the glove box light staying on.

Title: Re: Cosworth Battery Draining
Post by Simmo on Jun 27^th, 2015, 7:55am

Andy is correct but it seems that you have pulled ALL fuses. Has anything been fitted to the car that is directly connected to the battery or is it the battery itself which has failed? :-/

Title: Re: Cosworth Battery Draining
Post by Snoopy on Jun 27^th, 2015, 8:21am

Try disconnecting the alternator!

Title: Re: Cosworth Battery Draining
Post by KeithCEng on Jun 27^th, 2015, 9:26pm

Thanks to Andycan,Simmo and Snoopy for their inputs. I decided to double-check the accuracy of the clamp ammeter at low current levels by totally disconnecting the leads to the +ve of the battery while monitoring the current "clamped" around the -ve lead(s) - The current "drain" dropped from 0.6A to 0.3A which indicates that the meter is inaccurate at these low current levels (it should have dropped to zero!). I then connected a multimeter (DVM) in series with the +ve lead(s) to the battery - the drain current was 270mA, which dropped to 215mA after 5 minutes and then dropped to 85mA after 15 minutes (this was with all doors closed, bonnet closed and alarm "live") - This drain current seems to be in the right ballpark so it looks like either my battery is u/s or I need to drive the car for longer distances (I must admit I generally only do short trips these days).

KeithCEng

Title: Re: Cosworth Battery Draining
Post by Glyn on Jun 28^th, 2015, 1:59am

Had the same problem recently except took about a week to completely flatten the battery (to zero volts). Current drain less than 90 mA.
It was indeed the battery and a new one solved the problem.

Title: Re: Cosworth Battery Draining
Post by Mike H on Jul 24^th, 2015, 10:18pm

A clamp Ammeter only works with AC, not DC.

Title: Re: Cosworth Battery Draining
Post by a900one on Jul 24^th, 2015, 10:57pm

You can get clamp meters for AC and DC, but it is still better to get a meter inline to test low currents.

Title: Re: Cosworth Battery Draining
Post by PJDavis on Jul 25^th, 2015, 7:50am

Take the car for a decent run, more than 50 miles. Leave the car in the driveway for about 6 hours, then do a high-rate discharge for 15 seconds, that will test your battery! Take the car for the same run. Disconnect the battery and leave overnight, then put your meter across the terminals, you want it reading more than 12.5 volts ideally, but no-less than 12.35. Batteries don't seem to last as they used to, but modern cars have so much more electrics that the cheaper batteries can't cope. Buy a decent battery, it'll last longer and be able to withstand thos shorter journeys.