Bongo Fury

hi, does anyone know why the voltage is not stable at 12 volts on my bongo (2.5tdi converted). With the ignition on, but engine not running, voltage on cigarette lighter and other utilities is 11.3 volts. With engine running volts rise to 12.5-13 volts. Do i need stable volts as i am having trouble with my low coolent alarm being activated in driving. I am wondering if unstable voltage is the problem. The alarm has been replaced and rewired by the fitter, so any ideas on cause of problem would be appreciated as i am at a loss.

thanks john4700

I'm no expert, but your voltage sounds low for a healthy battery/alternator - I think you should be getting about 14V. I run an LED voltmeter on the bike (following a dead alternator event a few years ago...) & the voltage this shows can vary quite a bit depending on whether lights, heated grips etc are being used. So I'd expect the running voltage on the Bongo to vary depending on what you're using accessory wise, but sounds as if your battery/alternator combination might be suspect.

However there are others with far more knowledge of things electrickal on here, and one of them will no doubt be along shortly....
Rhod

Personally I'd check the voltmeter is working ok, as I don't think the bongo would start on that low a voltage Dodgy battery or loose connections/earth strap?

Can we assume the voltmeter is giving accurate absolute values (I ask becuase the relative values - engine off / engin on - sound reasonable). How eagerly does the starter motor turn the engine over - I'd expect it to sound strained at 11.3v. Out of interest, what were the circumstances that left you certain the voltage was too low to activate the coolant alarm (i.e.e were you trying the test as per the installation guide?)

the battery voltage was at 12.4, the voltage on the cigarette lighter plus other auxillaries was 11.3. also, i was following installation instructions.
should voltage vary on cigarette lighter whilst battery charging

Must admit it all sounds fairly healthy to me. Could be (must be?) poor earth on the ciggie socket. Do I take it you are ftting the Mk2 alarm that goes into the ciggies socket. I'd PM Haydn for advice if so and the socket is not going off on test. Good luck.

We have spoken about this and our conclusion is that the voltage in your system is not stable. The coolant alarm is sensitive to this and has brought it to light. I understand a 2nd hand alternator was fitted and was of unknown history. I would suggest that the voltage it is putting out is fluctuating and causing the problem with the alarm. Replacing the diodes in the alternator may fix it or a replacement alternator.

When running, the voltage across the battery terminals should be around 14.2 volts.........after stopping the engine this should slowly (3 or 4 hours) drop back to around 12.5 volts. The voltage at your ciggy socket should be the same (as near as dammit) as your battery....11.3 volts means you are losing a volt somewhere. This is a mystery.......
I would beg a alternator from somewhere and try it.. If it dosn't solve the problem then we must think again.
And to think ...you were quite happy till you fitted the alarm !!!

thankyou all for your responses, i will try your recommendations and let u know

Hadyn said

The voltage at your ciggy socket should be the same (as near as dammit) as your battery....11.3 volts means you are losing a volt somewhere. This is a mystery.......

The LED voltmeter on my bike is wired in to the ignition circuit, so it's slightly removed from the battery, & always reads about 1V less than the voltage measured directly across the battery. Could be inaccuracy in the LED meter (it's only there to give me an early warning of alternator failure, not as a precision instrument), but I've always put it down to natural drop through the circuit.