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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.

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  • \$\begingroup\$ Realistically you should seek practical advice from experienced people in your industry. For better or more worse most food trucks I've seen run a generator independent of the vehicle engine. \$\endgroup\$ – Chris Stratton Jul 26 at 14:35
  • \$\begingroup\$ Hi everyone in my area has static pitches so use a generator, I am the only mobile person, hence would prefer and inverter system. \$\endgroup\$ – Abcd123 Jul 26 at 16:03
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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.

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  • \$\begingroup\$ My inverter is rated at 3100w continuous proper, surely it would have at least 6200w to start the compressor. \$\endgroup\$ – Abcd123 Jul 26 at 15:09
  • \$\begingroup\$ @Abcd123 did you evaluate the compressor starting load? Without that knowledge... why do you say your 3000W has a 6200W capacity? Source for that or just a guess... \$\endgroup\$ – Solar Mike Jul 26 at 15:16
  • \$\begingroup\$ Hi the source is from specs listed online at \$\endgroup\$ – Abcd123 Jul 26 at 15:41
  • \$\begingroup\$ autosessive.com/products/61514/… \$\endgroup\$ – Abcd123 Jul 26 at 15:41
  • \$\begingroup\$ @Abcd123 add this info to your question properly, not everyone trawls through comments to piece together questions. \$\endgroup\$ – Solar Mike Jul 26 at 15:43
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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: https://www.fabcopower.com/generat/bgen.htm 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.

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  • \$\begingroup\$ Thanks for all your responses, the a generator would not work as there is not space in the van, and it is a mobile food van so goes from street to street. Hence the reason the engine will be always switched on anyway. The inverter has a watt meter ?? ( I think it’s called that) on it and the inverter switches of at around 1920w. \$\endgroup\$ – Abcd123 Jul 26 at 15:03
  • \$\begingroup\$ When I tried the machine at home ok mains, it worked perfectly and the compressor was on, is there anyway I can switch form mains at home to the inverter, whilst keeping the compressor (on the slush machine) switched on. \$\endgroup\$ – Abcd123 Jul 26 at 15:07
  • \$\begingroup\$ On the slush machine it says it draws 5.4A at 240v \$\endgroup\$ – Abcd123 Jul 26 at 15:11
  • \$\begingroup\$ Your question says 920W for the machine, but 5.4A at 240V is 1300W. But your wattmeter is saying the inverter conks out at 1920... can you measure the draw when connected to mains? Also, make sure the 12V wire to the inverter is big enough to carry the current. \$\endgroup\$ – hacktastical Jul 26 at 16:00
  • \$\begingroup\$ However star he it may seem, your right. The machine says 920w and 5.4A @ 230-240v. The wattmeter says 1920w. The inverter/batteries has previously been used with a slush machine (then unused for around 18 months) and now used again with a new machine, so I think the battery cables are okay. Could it be possible that the batteries are low on power? \$\endgroup\$ – Abcd123 Jul 26 at 22:17

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