Hardwiring an AC inverter (1 Viewer)

[robinhood4x4]

For one thing, those kinds of current will probably kill a standard relay pretty quickly due to arcing, plus I don't think inverters were meant to be switched on/off on the DC side like that. if you left something plugged in when you turned on your ignition, you could possibly cause power spikes that would destroy your appliences. It's probably not good for the inverter either. I think most inverters recommend a certain power on sequnce for connecting them.

Which is why you don't leave a device powered on during startup. As long there is little or now electrical load when the relays are fired, it should be fine. Also, I would assume Pete wants to wire it so the relays aren't dependant on the ignition so starting the truck won't cause the relays to de-energize.

But you're right, dont' leave anything "on" when you start the truck...the inverter doesn't like it. I had my laptop plugged in while playing a game (waiting for my wife at the eye doctor) and I started the car for some reason and the low voltage alarm on the inverted went off. Now the inverter beeps at me when it's working hard.

Pete, www.12voltguy.com has some 100 amp solenoids for $45 if you want to go that route. Also has some fuses and holders that go up to 175A.

 

[ducktapeguy]

Also, I would assume Pete wants to wire it so the relays aren't dependant on the ignition so starting the truck won't cause the relays to de-energize.

Hmm...I assumed just the opposite, it sounded like he did want to wire it to his ignition? Maybe I'm confused, but I thought he wanted the inverter to be triggered by the ignition switch, so the inverter is only on when the ignition is on and turns of when the ignition turns off.

I also assumed (maybe wrongly) that there would be a load connected to it during startup. Because if it was turned off with no load, then there's no advantage to wiring a relay in there, it's like having two switches in series.

 

[firetruck41]

If you shouldn't leave anything on when starting the truck, it makes the "ignition on" relay kind of pointless, you will have to unplug or turn on/off the equipment anyway. Might as well forget the relay and just flip the switch (which you have to do anyway).

 

[aamiggia]

My recommendation is based on the following assumption.

ASSUMPTION:

The 3 fuses in parallel go to 3 separate inverters inside the inverter case and then 3 separate AC outlets. So the path is:

battery --> 125 A fuse --> distribution block on inverter case --> 35 A fuse 1 --> inverter 1 --> AC outlet 1

... --> 35 A fuse 2 --> inverter 2 --> AC outlet 2
... --> 35 A fuse 3 --> inverter 3 --> AC outlet 3

This is probably how it is, but just in case I don't want you to burn up your cruiser. If all 3 fuse tie into 1 inverter then don't do the following, but I can't see how that would work. Parallel paths are parallel for a reason, basically they are 3 separate circuits.

If you have 3 outlets chances are the max power draw for each is 35 A x 12 V = 420 W x 90% inv. eff. = 378 W - 1/3 for power spikes = 252 W per outlet. This is exactly what the unit is rated for 750 W total / 3 AC outlets = 250 W / 120 V = 2.1 A. What's the load rating for each AC outlet?

Recommendation:

Down stream of dist. block on the inverter case you can wire the 40 A relays in parallel, one going to each fuse. I would suggest that you only wire 2 of the 3 outlets to relays. That way you can leave one hot when the ignition is off.

The max draw for each AC outlet is 35 A on the DC side, if you draw more than that from the AC side, the fuse will protect the circuit and the relay. The current through the relay will only be as high as the load requires, which is protected by the fuse. Technically from the above math you have 378 W / AC outlet or 3.15 A. I wouldn't run a toaster, but small motors, air mattress pump, laptop, etc.

The Toyota Service Technician training manuals I'm reading are paying off.

 

[firetruck41]

Not sure about that, though with the 3 fuses that could be the case. Most inverters advertise the fact that a 400w unit can power a ??? 300watt appliance, while a 800w unit can operate a ??? 750w appliance, etc. They are capable of the stated output from one outlet, not 1/2 of total wattage x 2 outlets. His inverter may be different than some of the ones I have been looking at though.

 

[aamiggia]

That's totally possible, hence the disclaimer. I've never taken a unit apart to see how it works.

The simple check is what is the max. load (AMPS) for each outlet. If it's 2.1 A then you have 3 separate circuits, 1 for each outlet. If it's 6.3 A then you have what Firetruck has said and avoid my recommendation.

 

[robinhood4x4]

Hmm...I assumed just the opposite, it sounded like he did want to wire it to his ignition? Maybe I'm confused, but I thought he wanted the inverter to be triggered by the ignition switch, so the inverter is only on when the ignition is on and turns of when the ignition turns off.

Woops, missed that part.

 

[Pete483]

Aamiggia - I took it apart already and it is wired in parallel prior to the inverter in that from the hook up on the outside, three 10 gauge wire go to three fuses and then join back into one wire.

I was also planning on running a swith between the relays and the ignition to control the inverter. Basically, the point of the relays was to avoid running down the battery if accidentally left on.

However, ducktapeguy's idea of relaying the on/off switch makes a hell of a lot more sense.

Therefore, it should work as follows:

Inverter is wired straight to the battery--fused on battery box
Relay interupts on-off switch unless ignition is on
Switch on the dash interupts relay for starting and when inverter is not needed.

 

[Boston Mangler]

Here is a diagram of my setup