Battery Drain within an hour

[Jake89]

Looking for a little direction

I have a w203 Mercedes c220 CDi and its currently killing my battery within an hour. My battery is fine, alternators charging etc. but it's drawing 26 amps when the cars turned off.

I've done a search and the electric seats seem to be the common fault, but would it draw 26 amps? That's quite a lot, i've been advised to check glow plug relay.
Does anyone have any other suggestions or are their any known common faults? Electrics isn't my forte really but don't really want to take it to a Merc Garage £££

Thanks

 

[grober]

You might have a faulty diode pack in your alternator? Try disconnecting the main charging lead- careful its always live to the battery. or borrow a clamp meter Uni Trend Autoranging AC Digital Clamp Multimeter | Maplin

A GOOD AUTO ELECTRICIAN should be able to help at far less cost than MB

 

[Jake89]

OK mate, i will try that tomorrow. Just waiting for the battery to charge again overnight.

 

[Dec]

One thing that’s ON when the car is off is the car alarm, is it working properly?
Maybe its currently frying itself… https://www.google.ie/search?q=merc...hVHtg8KHfQ***4Q_AUIBigB#imgrc=NWdWBh6eiyP33M:

Dec

 

[Jake89]

Haven't noticed, but i'll have a look at that as well

 

[richard]

Alarm on a small fuse, so not 25A.

25A, something is getting hot. You should be able to find it by heat. I'd very strongly advise against disconnecting the alternator power lead whilst the battery is connected. Disconnect battery ground lead first then disconnect alternator power lead and insulate well, then use decent ammeter to measure current draw between battery and ground. If its something small it was your alternator diode pack

R

 

[Jake89]

If my diode pack has gone on my alternator, would it still charge my battery?

 

[whitenemesis]

I'd suggest the booster heater, well known for short circuiting and killing the battery.

Should be located on the side of the engine, easy to test, simply disconnect the big fat power cable...

 

[Ted]

At 300 watts something is getting hot enough to warm your hands on
Shouldn't be too hard to find.

 

[grober]

Alarm on a small fuse, so not 25A.

25A, something is getting hot. You should be able to find it by heat. I'd very strongly advise against disconnecting the alternator power lead whilst the battery is connected. Disconnect battery ground lead first then disconnect alternator power lead and insulate well, then use decent ammeter to measure current draw between battery and ground. If its something small it was your alternator diode pack

R

YES you are absolutely correct of course I took for granted the OP would know to do this -- but should not have assumed it.

 

[Jake89]

YES you are absolutely correct of course I took for granted the OP would know to do this -- but should not have assumed it.

Haha its ok, i know. Thankyou.

 

[ivan1983]

To help find which area its in could you not start by pulling one of the bigger fuses and see if the battery stays charged? When the battery stays charged at least you know what fuse its associated with

 

[MancMike]

At 25A 12V you should be able to tell which it is by seeing which fuse sparks as you go to plug it back in. No need to wait to see battery drain.

 

[BTB 500]

Yup I'd go via the fuses.

PS if a 26A draw is flattening your battery in an hour then you also need a new battery!

 

[190]

PS if a 26A draw is flattening your battery in an hour then you also need a new battery!

Possibly but it depends on the size of the battery. You can't assume that a battery that discharges 26 amps for 1 hour has a capacity of 26AH. It will be more like 52AH.

Batteries are rated at a 10 or 20 hour discharge rate so an 80 AH battery will provide 4 amps for 20 hours. Due to Peukert's Law if you increase the current beyond 4 amps the capacity of the battery is reduced and by the time you get to a discharge rate that flattens the battery in 1 hour the batteries capacity is approx. halved so that even a new 80AH battery will only provide approx. 40 amps for one hour.

 

[boyt]

Sounds like the booster heater on the engine block on the left side of the block, you can disconnect the main feed wire from the profuse box if I remember correctly, if you PM me your chassis number I can check which fuse it is,

 

[BTB 500]

even a new 80AH battery will only provide approx. 40 amps for one hour.

True. On the same basis (20 hour rated discharge time and Peukert constant of 1.3) a new 70Ah battery would be expected to give 38Ah when discharged at 26A.

So an effective capacity of 26Ah would mean a constant of 1.5 instead, which would suggest an aged/deteriorated battery.

 

[Jake89]

WDB2032082F684610

Cant send PM's yet boyt, thanks.

 

[whitenemesis]

I didn't think the booster heater/control module is fused, which is why when it malfunctions it drains the battery.

IIRC, the CDI control module instructs the boost heater control module when to operate (Multifunction display option set to Automatic or On and ambient temp ,8c and coolant temp ,78c).
The booster heater control module then detects excess capacity via the alternator reg pack and takes power directly from the alternator output to the heater element.

 

[Jake89]

Where do i find the heater booster to disconnect it? It's on the LH side block, is it under the airbox?