Running a battery charger from a power inerter

[pierreeich]

Hello all,

I have a trailer mounted machine which runs on 24v D.C. (two 12v batterys).

I wanted to charge up the machine batterys while towing it behind my car so I bought a power inverter to run the existing charger from my cars 12v D.C. battery supply.

I have wired it up today and have power to the inverter. The inverter is 500w and the charger draws about 185w when plugged into the mains.

The problem I have is that when I plug the charger into the inverter, nothing happens. The needle on the dial stays at 0.0.

Is there some reason why this kind of charger cannot be run from an inverter or am I missing somthing.

Any help would be very much appriciated.

 

[GreenGiant]

Have you checked to make sure that the inverter works with other things?

does the car have to be on for the (im assuming) cigarette lighter plug to be active?

 

[Harald Kapp]

Let me repeat to see whether I understand correctly:

Your car has a 12 V battery (as usual)?
The inverter generates 115 V AC (or 230 V) I assume, right?
The charger runs on 115 V AC (or 230 V)?

Did you measure the output voltage of the inverter without and with charger plugged in? Which results did you get? The dial is on the inverter or on the charger? Does the charger indicate that it has mains power?

One reason your setup doesn't work as expected could be the waveform of the inverter's output. Most inexpensice inverters do not generate a sine wave (as is the waveforms of standard mains voltage) but generate a more or less square waveform. There is a chance that the charger does not comply with that kind of input voltage.
Another reason may be that the charger, a nominal load of 185 W notwithstanding, draws a much higher inrush current when switched on (or plugged into the inverter). For mains this is normally no problem, but the inverter may recognize this inrush current as a short circuit and may shut down the output to avoid damage. If this is the c ase, you could try to put an NTC (thermistor) in series between inverter and charger. However, there is no guarantee that this will work and it means that you are going to handle dangerous voltages. So dont do it if you lack experience with that kind of voltage!


Harald

 

[pierreeich]

Thanks for the advice.

The inverter works fine with other mains voltage devices and cuts out giving a bleeping sound and the fault light coming on when the power needed is too great. The charger also works fine from the mains.

I would suspect that your theory about the wave form would be correct. I wonder if an older charger would work rather than the new one that is currently fitted.

 

[Harald Kapp]

Does it give that bleeping sound and error light when you attach the charger? That would be more an indication of the charger drawing to much inrush current on power on (not a fault of the waveform).

Harald

 

[pierreeich]

No, its not. That's why I dont think its overloaded.

I'm looking at a "Pure Sine Wave" inverter on ebay. Do you think that would do it?

 

[Harald Kapp]

There's no guarantee. I doubt it.
Have you measured the waveform of the inverter?
What are the specs of the inverter and charger in terms of peak current?

Another idea, foregoing inverter and charger completely:
You could wire the trailer's batteries such that by throwing a switch they are in parallel instead of in series. Thus you'd have a 12 V battery which you can connect in parallel to the car's battery and use the car's charger.
If you want to use the trailer, throw the switch back to normal position, putting the trailer's batteries in serie to have 24 V.

Harald