12v Invertor woes

[LeCCy]

I use a small polco 12v inverter in the Bongo, which works fine with everything (laptop,phone charger) when the engine is running but with the ignition off it goes into a fault mode when powering the laptop ( still works phone and a battery charger fine)

I dont have the box/manual anymore for the invertor but I assume that the red light means that there isnt enough current for the device being powered? The laptop charger is 90w I think but still I have the twin battery setup in the bongo so they should have some ummph, and I have no probelms with engine starting. ( apart from last week when I left the lights and fan on for 90mins -doh!)

Is there a way to check that my batteries are ok with just the small multi meter I have? The Voltages are fine at just above 12v.

Thanks for any advice
Russ

[grumpo]

If the traction batteries are good enough to start the engine from cold,
then they will be more than good enough to run the inverter.

The red light usually means that the output transistors have shut down
due to over temperature normally caused by excess current.

If the inverter is as you say, small, it could be that the computer battery
is fairly low and requires a constant charge which may overload the
inverter, whereas an intermittant charge may not.

Try charging the computer battery fully using the mains supply and then
use the inverter again and see what happens.

[pippin]

I suspect that the inverter is sensing low voltage due to voltage loss in the thin wiring to wherever you are connecting it in the Bongo.

At 90W, the inverter is drawing 7.5A which can cause a significant loss in thin wiring.

The reason it works when the engine is running is that the alternator is raising the voltage just that bit higher to prevent the low voltage cutoff from operating.

You would do well to run it from a connection direct to the battery, via the obligatory fuse of course.

[LeCCy]

Thanks for replies gents.

I think that you are spot on Pip. I nipped out to test Grumpos theory after charging the Laptop to 100% and found that the fault signal comes in when the vDC at the invertor input drops below 10.6.

With the engine running the voltage is over 12, with the alt off it is generally around 10.7v but drops below this for periods quite often.

Pippin, are you saying I can just run two cables straight off the battery terminals into the passenger footwell or somewhere? What size fuse 10a? Thanks lots
Russ

[pippin]

Yes, that is probably your best bet.

You could even use the existing ciggy socket by disconnecting (and insulating) the existing connections.

[dandywarhol]

Is the laptop charger 90W at 12volts or 240 volts?
I'd be surprised if a laptop charger demands 7.5 amps - thats twice a coolbox consumption