I sell vinyl decals, and I'm wanting to set up a roadside stand this weekend. In the past, I've used a generator for power and an APC to clean it. My APC died over the winter, though, and I'm afraid to run my electronics off of raw generator power, having lost stuff to generator power surges in the past.

I'm wondering if anyone here can tell me if I should be able to run completely off battery power, and for how long. I have two inverters; a 75W and a 300W. I'm planning on using the 75W to connect my laptop, which draws 65W. I've done this many times in the car off the vehicle's electrical system without issue. The second is the one I'm concerned about - I can't find a power requirement for my vinyl cutter. All I can find is "90-260V AC", and that the power supply outputs 6, 12, 18, and 36V at 1 Amp. The fact that it lists the input voltage as "Power requirement: " makes me want to smack the Chinese kid that put it together.

My understanding is that a car battery holds about 45 Amp-hours at full charge. Here's my math to calculate how long I would get with my setup:

My 65W laptop charger will pull .591A at 110V. The car battery is 45Ah, so divide that by .591A, and I get about 76 hours of use from my laptop off a fully charges car battery.
Assuming my cutter draw 150W (a high guess I think), then you have 1.364A, and 33 hours of use.

If that's right, then I should have no trouble with eight hours of constant use - and of course, my cutter wouldn't be on all the time.

I have two things to ask of Arfcom - first, will the power from an inexpensive inverter be a risk to my equipment? I wouldn't think so, but it's worth asking. Second, are my calculations correct? Being able to run both of those things off a car battery simultaneously for over 24 hours seems high to me.

Your math is right, but you need to know that the battery may not provide enough voltage to run the inverter(s) once it gets to around 25% power or so.  You will also have some of power loss from the inverter, how much really depends on the quality of the inverter.  You could minimize this by running both items off the single larger inverter, if it will handle them both.

A standard car battery won't tolerate a lot of cycles where it is drained to the 25% mark. If this was going to be a permanent setup for you I would recommend a deep cycle battery.

in theory you would have more problems with the modified sine wave from a cheap inverter then you ever would even with a cheap generator. i have run a multitude of these so called "sensitive" electronics without a problem as has thousands and thousands of weekend campers and retired people that travel the country in campers every day of there lives.

I've been in a very similar situation - Harbor Freight 800 watt generator worked like a champ.  I stuck a UPS on the generator, then plugged everything in there.  Bonus points - you can shut the generator down to refuel / etc. that way.

For what you're looking at, I would feel better with 2 or 3 batteries in parallel.

I have a generator, but it's a 5000W Honda - loud, expensive to run, and just generally overkill for this. I have 2 good car batteries and I think I can lay hands on 2 more tonight. They're all side post, so I think I'm going to build a cabinet on an old two-wheeler and use that from now one. Bonus points if I can use it to hold up a sign or something :)

I do need to get a new UPS first though.

Oh? I thought the power from a generator was inherently dirty - I lost a desktop PC to one when I was a teenager, and have been leery of them since.

It's not so much that my stuff is sensitive - it's that the cutter is cheap Chinese crap, and is likely very prone to things like fluctuations in power supply.

no you didnt. you lost a PC because it had a crappy power supply, not a crappy power source. it also could have been lost because it was just its time. electronics are a funny beast. i have seen power supplies last years and have seem them last less than 6 months, its a crap shoot. unless something is wrong with the generator there is no reason it would damage anything plugged into it. for piece of mind you can buy a DMM to test the voltage and Hz before you plug anything in to it.

You're going to be really, REALLY disappointed with the lifespan of those batteries. Two or three decent discharges, and they'll never be the same again. They just ain't designed for that kind of service.

You need deep-cycle batteries.

Sam's and Costco both sell 6 volt golf cart batteries for around 80 bucks apiece. Connect two of 'em in series, and you've got a 12 volt battery bank that's almost bulletproof.

Archived thread of all you need to know.

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