Vehicle Alternator/Inverter system

Electrical Engineering Asked by Abcd123 on September 15, 2020

I have a food van with a stock alternator on the engine, and a 3000w inverter setup. The inverter setup uses 2 Trojan leisure batteries. Somehow the inverter setup is also linked to the alternator (I’m sure of this). I have only ever used this for small items like a travel kettle or phone charging. Today I purchased a Slush machine which is rated at 920w. I tried it on the inverter and it ran for a few mins, however as soon as the compressor kicked in the inverter switched off.

The inverter is rated at 3100w continuous power, and 6200w peak power for 1 second.

When the compressor kicks in and inverter switches off, the watt meter on the inverter displays 1920watts.

Now obviously it’s clear that the inverter cannot run the slush machine, so I was wondering what possible solution there are out there.

I should also add that the inverter and batteries were not used for around 18 month prior to fitting the slush machine. What would be the best way to test their batteries? Voltmeter?

I was thinking of adding a second alternator in the engine, would this work to provide enough power to the inverter and it’s batteries to power the slush machine.

2 Answers

I would test the Slush machine on a known stable supply - you need to establish the starting characteristics of the compressor.

Some recommend that the inverter capacity has to be 5 times the rated load... 5 * 920 = 4600W, so you will probably need a different inverter or consider the other solutions from hacktastical.

Answered by Solar Mike on September 15, 2020

Can you borrow a current meter and see what the slushy machine is drawing when the compressor kicks in? Then try the same test, using the inverter to see what's tripping it up. Maybe your specific inverter isn't up to the task, but another one might be. Or there may be an issue with the wiring to the inverter (too much IR drop maybe?)

To your thought, they do make 110V alternators for underhood. Example here: Major drawback of this approach: you have to run the engine at a specific RPM to get the correct 60Hz, so that means something to set the throttle, too. Your customers won't like breathing the engine fumes or hearing the noise.

A sure-fire solution (and possibly cheaper, considering installation) would be a small gennie to run the machine.

EDIT: check the battery condition. If they’ve been sitting unused they may have sulfated and thus will not be putting out enough peak current for the compressor start-up.

Answered by hacktastical on September 15, 2020

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