Compact Car Alternator & PS Inverter

[Larry619]

Question: What is a safe continuous amperage draw from a compact car (2008 Mazda 3) alternator for use with a pure sine wave inverter?

Background: I built a LiFePO4 24V portable solar generator. The battery is connected to a Growatt 24V3KVA. I use the AC Input to recharge the 24V battery when there’s no solar. The AC charging can be configured anywhere from 1A to 60A (24w to 1400w) charging.

I already have a gas inverter generator (Firman 1600w) and it charges at full speed nicely - but at full throttle it’s very loud in my townhome complex.

I’d like to try using my car connected to an inverter but I worry about overwhelming the electrical system - also the reason why I don’t want to mess with DC-DC solutions just yet. The car could be a more discreet (but inefficient) way of charging in an emergency. The PS inverter would be hardwired to the car battery. Likely scenario would be unattended charging at idle engine speed.

Would charging at a continuous 200w (12v ~ 20A) be okay? What about 400w continuous (12V ~ 35A)? I’d be hesitant trying to push 1000w for rapid charging, especially at idle.

Other thoughts on discreet charging so I don’t disturb the neighbors?

 

[camelCase]

A 2008 Mazda 3 came with a 90 amp alternator, which would be around 1200 watts peak. To keep it from melting itself down you'll want to derate that by a lot. 400W would be on the upper end of what I'd be comfortable with. 200W would be better.

 

[Larry619]

A 2008 Mazda 3 came with a 90 amp alternator, which would be around 1200 watts peak. To keep it from melting itself down you'll want to derate that by a lot. 400W would be on the upper end of what I'd be comfortable with. 200W would be better.

Nice! Straight to the point.

My current 24v battery is 70ah, it would take quite a while at 200w from empty but good to know I should avoid using the car - this will probably be last resort.

 

[pollenface]

I ran a 2000w psw inverter from a car with a 110a alternator ... it never really got thrashed, the biggest thing I ran was a 750w grinder

I think you pull about 38amps for every 1hp (746w)

 

[12VoltInstalls]

I think you pull about 38amps for every 1hp (746w)

At 12V from the car alternator?
I’d expect ~67A draw factoring efficiency and 12V nominal +/- 800W. Unless I missed the point somewhere

 

[camelCase]

Large interment loads aren't likely to harm the alternator, it's heavy continuous ones that will overheat things.

 

[yodamota]

Have you considered a higher output alternator? Or even adding a second alternator for this purpose? I really don't know the engine bay of mazda 3s. A second alternator might be moot if there is no room.

 

[12VoltInstalls]

Large interment loads aren't likely to harm the alternator, it's heavy continuous ones that will overheat things.

I wouldn’t sweat it.

Seeing what jeep club members do with their winches will convince you that alternators aren’t as wimpy and pansy as a lot of people think.