CONVERTER OUTPUT ?

HF 400 watt is most likely an MSW... You have just about the minimum amount of battery for that size inverter (you need 200 amp horus per kilowatt you have 0.4 KW or 80 amp hours, A Group 27 is about 90 amp hours)

But there is a long, long, list of things that do not like MSW inverters, this includes a lot of electronics and some motors.

The last entery on the list is "Anyhthing needing too much power"

If you get a TRUE SINE inverter.. Then the list is much shorter,, In fact it has but one entry "ANything needing too much power"

Also, starting requirements can be many times operating power requirements

Though I'd think 400 Watts SHOULD run a fan


Finally,, how is the inverter connected... Plug in or hard wired. (12 volt side, 120 volt side does not matter)

hard wired much, much, much better Plug in only good for about 100 watts if that. If you can (if the power leads are such you can upgrade them) I would use 4GA starter cable, 3 pieces, and a fuse (one holder and fuse) 50 amps or so, to hook direct to the batteries.

My $12 150 watt inverter, that doesn't even have a fan in it, runs TV, DVD, computers, PA sound system, small scooter and automotive batt chargers, and even my little 1 gallon pancake air compressor, but it will not run a little box fan correctly, same as my 1500 watt would not run the microwave correctly. And if you hang an AC volt meter on a MSW, you will really wonder whats going on. So, don't question it, it is what it is, it either works, or it doesn't. MSW has worked well for my needs, If I absolutely needed anything that didn't, I would spend some money on a PSW.

Very true, Mr Wizard, the Tripplite and Freedom inverters are at the top of the MSW class. The Harbor Freight products are not, though.

If the devices in question operate fully when on utility power and won't run on the HF inverter, there is little deduction needed to pinpoint the problem.

The problem is no surge capacity, it can't handle the fan inductive load
Or the C-pap air pump


my $300? PV1250 weighs 22#, and has NOT let the 'Magic blue Smoke' out of anything in this RV in 6yrs of everyday use

The cheap parts store inverters are getting to the point, where there is almost to copper in them, no wire wound inductors, no transformers
It's all digital chopper chips changing the voltage
They are only good for supplying 120v power into other electronic switching power supplies

Edit: previous post belonged in a different thread,
Corrected this post

After suffering numerous noxious polyvinyl and discrete component emissions I wised up and bought a 300 watt Samlex. A cheap inverter will destroy a BiPAP Respironics unit. Playing yes/no Kiowa Telegraph wore thin very quickly for me.

joebedford wrote:
Lots of motorized thingies won't work on a MSW inverter.

Ditto: For example, many electric blankets or warmers will cook the controls. We have let the smoke out of several.


What it means is dirty electricity versus clean. Remember when mom used to use her sewing machine and it messed up the tv? Well, kind of like that. Some electronics want clean sine waves and not jagged waves.

Lots of motorized thingies won't work on a MSW inverter.

Oasisbob wrote:
The converter has served us well for TV etc,. Still does. I have my Harbor Freight horror stories but this is not one of them. Or is it? I am really stumped. Is there a way to test the output of this converter or what?

I don't buy any electrical gear from HF after some bad experiences. Yes the output can be tested but you are unlikely to have the required equipment and you wouldn't want to buy it either. If you know someone with an Oscilloscope they can check it.

My CPAP works off my modified inverter. It draws 80 watts.

Look closely at your friends CPAP machine. Does it have a square transformer in the power cord?
If so it is most likely 12 volt already. Many are.
If it is just buy a 12 volt cord for the machine. No need for inverter.

But just for funs what is the amp draw of the CPAP?
400 Watt only gives you about 3.4amps and if it has a built in water heater for humidification that could be more than 3.4 amps