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4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Sun, 20 Oct 2019, 21:59
by arnolde73
Hi everyone,

I drive a Peugeot Ion (identical to C-Zero and I-Miev) with a 350V/16kWh battery and since I do a lot of outdoor work around my property (fencing, gardening, welding, pumping, etc.) I'd like to add a high power (16A) 230V socket to my Ion. All I could find so far are 12V-to-230V inverter solutions which are only good for <1000W and only for short times, since the 12V battery and it's onboard charger are obviously not upto high loads.

Has really noone ever put a (280-380V) 350VDC to 230VAC inverter into his car (connected more or less directly to the main battery)? It seems so obvious to me? And since the voltage conversion is pretty slight, it should even be pretty efficient (>95%?)...

kind regards,
Ethan

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Sun, 20 Oct 2019, 22:40
by coulomb
arnolde73 wrote:
Sun, 20 Oct 2019, 21:59
Has really noone ever put a (280-380V) 350VDC to 230VAC inverter into his car (connected more or less directly to the main battery)?
I've not heard of it. You'd have to get access to the inverter's DC bus, arrange for pre-charge and suitable DC rated fuses, and somehow safely get access to the car's battery. This traction battery access would have to be water and dust proof, and finger safe. You could use the CHAdeMO outlet, assuming you have one installed, but the connectors are very expensive and hard to obtain, and you'd have to somehow send magic undocumented CAN commands (or something) to close the CHAdeMO to battery contactors.

I suppose if the inverter was to become a permanent part of the car, you could make a permanent connection somehow, but it all seems fraught with danger. I'd say this is why you don't hear about this being done.

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Sun, 20 Oct 2019, 23:43
by arnolde73
Yes, it's supposed to be permanent, inside the car, and I wouldn't want anything plugged into the Chademo outlet. But maybe I could tap onto the DC wires leading to the Chademo socket... and maybe I could rewire the Chademo contactor coil so I could alternatively close it with a manual switch. Or maybe I could use the DC supply to the electric heater (5kw) or aircon (both 350VDC)... maybe I'll check the car's wiring diagram. Accessing 350VDC shouldn't be that hard with a little thinking. At least the 5kW heater supply should be strong enough and also already fused.

What did you mean by "pre-charge"?

Maybe an old UPS can be modified... just need to find one that doesn't invert the 48V and then transforms that up, but has a (approx) 350V DC bus and makes a sinewave directly from that. For my purposes the output voltage wouldn't even need to be regulated very well, could easily range from 200-250VAC.

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Mon, 21 Oct 2019, 08:26
by coulomb
arnolde73 wrote:
Sun, 20 Oct 2019, 23:43
What did you mean by "pre-charge"?
The inverter will have large capacitors on the DC bus. These have to be charged up to within about 20 V of the battery before connecting directly to the battery. Otherwise, whatever contactor or switch you have between the battery and the inverter will have a very hard time, and the capacitors will be extremely stressed, and won't last long. So you have to have a resistor in place first, then short the resistor after a suitable delay. That resistor has to be able to handle a very large pulse power; there are some resistors made for that very purpose (e.g. can handle 25 x their continuous power rating a fraction of a second). This usually means two contactors, although the one doing the pre-charge can sometimes be a smaller one, as it handles less current.
For my purposes the output voltage wouldn't even need to be regulated very well, could easily range from 200-250VAC.
Ok, but usually the output voltage will be fixed. If that's say 230 VAC, then you need at least 230 × √2 = 325 V, plus various voltage drops, so at least 330 V on the battery, or the output will start clipping. That might not bother some loads, but it could be a problem for others. You might be able to fiddle with voltage sense resistors to change the fixed output voltage.

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Mon, 21 Oct 2019, 12:28
by Richo
You'd also loose the isolation as that is done going from 12V-400V prior to the DC bus.

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Mon, 21 Oct 2019, 12:57
by T1 Terry
If the PIP5048MG inverter was used with the battery connected to the solar input, would the capacitors still need to be precharged? Or would the inverter already have this as part of the design?

T1 Terry

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Mon, 21 Oct 2019, 13:52
by antiscab
it would still need pre-charging

This is true of grid tie inverters too

solar panels are nominally current sources, so their short circuit current is only little bit more than their maximum power point current.

batteries are nominally voltage sources, so their short circuit current is several orders of magnitude greater than their normal operating current.

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Mon, 21 Oct 2019, 14:44
by T1 Terry
Thanks Matt, makes sense that the solar would gradually charge the caps till the desired voltage was reached and then the system would turn on. if this isn't part of the inverter design then it would need to be added for using an EV battery to power the inverter. I know with the 48v MS model inverters, unless a light bulb is used as a visual indication resistor to charge the caps, the arc is enough to blow the end of the crimp terminal away and require a coffee and a sit down for a while to settle the nerves :lol: They can be rather tough on a Gigavac as well on a 48v lithium system, not so bad on the 24v systems and not an issue on the 12v systems unless an under rated Gigavac is used.

T1 Terry

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Tue, 22 Oct 2019, 11:13
by T1 Terry
More thoughts on this inverter. If the 48vdc battery was also used, wouldn't that keep the caps charged because it would be powering the inverter when the EV wasn't plugged in?
.
T1 Terry

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Tue, 22 Oct 2019, 12:49
by Richo
Sorry why couldn't an industrial motor controller/inverter be used?
couldn't one be be tricked into outputting 240Vac 50Hz.

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Tue, 22 Oct 2019, 13:11
by antiscab
Richo wrote:
Tue, 22 Oct 2019, 12:49
Sorry why couldn't an industrial motor controller/inverter be used?
couldn't one be be tricked into outputting 240Vac 50Hz.
it would need an output inductor (field windings off an old induction motor maybe?), and also likely a minimum load

it would be interesting to try out

I have thought about using a vfd feeding a star connected set of 3 single phase transformers pinched from old transformer based grid tie inverters (or even using them insitu)

Inverters built for the purpose can be probably be bought by the time I get around to trying it out

Re: 4kVA Inverter for 230VAC off a 350VDC battery?

Posted: Tue, 22 Oct 2019, 18:36
by coulomb
T1 Terry wrote:
Tue, 22 Oct 2019, 11:13
More thoughts on this inverter. If the 48vdc battery was also used, wouldn't that keep the caps charged because it would be powering the inverter when the EV wasn't plugged in?
.
Yes, that's right, though then you really have to pre-charge the 48 V capacitors to avoid the need for the nerve calming coffee :o

The other problem is that it may pre-charge to the wrong voltage; a bus voltage that is 60 V too high is not as bad as 360 V too low, but still bad.

In fact, the inverter probably has a small pre-charge power supply that runs off the 48 V supply. But again, it won't know to stop at 360 V or whatever the EV battery is at. When you pre-charge from the battery that is about to be connected via a resistor, the capacitor voltage gets asymptotically closer and closer to the battery voltage with time (ignoring the voltage divider caused by idle load). So as long as you wait long enough, you know it will be very close to the right voltage for final battery connection.