Thursday 1 October 2009

Van Saga Continues

Well, after various adventures and hoop-jumping I now have a down-plated 416i Mercedes Sprinter designated as a 3.5 tonne van. It even passed it's class 7 MOT. Some more hoops yet, but progress is being made.

My mechanic reckons the battery is being drained by the tachograph, which I now see no reason to keep. In fact, when funds allow, the space would be better taken up by a CD player.

The blessed tachograph instruction book funnily enough doesn't give any clues on how to remove the bleeding thing. Any advice and idiot proof instructions welcomed!

The Penguin


tacho man said...

Check your manual and find out which fuse it uses. Remove the fuse and at least it won't drain your power until you replace it with a stereo.
It's probably removed with the special headed ratchet bit. Usually hex or star shaped.
I've also got a digi tacho card for my job. Miles better than the old paper thing. That was a pain in the arse.

tacho man said...

Oh, the fuse box location will be in the Mercedes manual. Usually the fuse box is in the glove box or at the back of the engine up high somewhere.

Anonymous said...

Sorry, the above is incorrect. The Tacho will not have a separate feed as drivers used to pull the fuse in order to appear as if they were on a break. It will also most likely be linked into the Speedo. Any half way competant auto electrician, or tacho workshop will be able to remove it, and give you some cash for the head. Many Sprinter fuses are under the drivers seat,open the door and you will see a removable panel. Fuses are behind that.

Demetrius said...

Leave it unlocked down our street, it will soon be gone. As with anything else left in.

Anonymous said...

If the tacho is switched off it should not be draining the battery, once the vehicle is running, it is irrelevant. Anyway, a likely culprit is the alternator, either not charging, test with a voltmeter or it is discharging (backfeeding) through the regulator. Prove by measuring current drain with alternator regulator connected and then not connected.

mr fixit said...

Anon 20.09
Not really. The digi tacho needs to keep it's memory powered. Time, card user etc so it will always draw power even when switched off.
The altenator is fine as everything else is working.
"backfeeding through the regulator"
Now I know you're a bullshitter !
You can easily check the alternator by putting a meter across the positive and negative terminals of the battery. It will read 12V with engine off then 13.5V with engine running if alternator is working.

Anonymous said...

Mr Fixit, if 25 years as an electrical engineer makes me a bullshitter then so be it. I was trying to put into layman's terminology the fact that most mystery battery discharges are caused by one or more of the output diodes becoming faulty causing the permanent connection to the battery positive to find its way back to earth. If you've never heard of that then I can only conclude that you are a it of a thicko in electrics. "The alternator is fine as everything else is working" what? Electrical loads will work just fine until such a time as the battery gives up. Why are you struggling with the basics, check your alternator charge, check it is not discharging via the output connections and then look at other stuff. Oh and by the way, a digi tacho load is designed to be rather small, unless the vehicle is stood for a long time, this will not be enough to discharge the battery. But you know best, what are you qualified in = knitting? Dick-head.

microdave said...

"It will read 12V with engine off then 13.5V with engine running if alternator is working."

If that's the case you have a seriously buggered electrical system!

A fully charged battery with no load should be reading at least 12.6 volts, and preferably nearer 12.8 And alternators normally regulate at 14.3-14.5 volts. The only time you might see as little as 13.5 volts is if the engine is idling with absolutely everything electrical switched on.

I'm with Anon on on this one - you don't know what you're talking about.

The only guaranteed way of identifying the source of battery drain is to put a multimeter set to a current range in one battery lead, and then remove each fuse in turn. This needs to be done with every thing turned off, and will show up things such as a glovebox light that's not switching off. If this doesn't identify the culprit then you have to start disconnecting anything directly wired to the battery - the alternator being the most likely. But there can also be unfused feeds to engine management and ABS brake systems. Anything drawing more than a few milliamps will give problems if the vehicle is left standing for long periods.

You will probaly need the vehicle wiring diagram to see exactly where all the feeds go to.