OT(ish) - car battery / typical ampere-hour rating ?

Youll kill a car battery stone dead deep discharging it like that, need a deep cycle or leisure battery, typically 85-110Ah, take it mebbe 80% actual useable , so 3 off 85Ah batterys plus big invertor might power it, needs himself in the van at same time... Uprated alternator,genertaor or really good insulation might be more practical.

Adam

A generator would be more practical, but its for a mobile food delivery van - I was thinking the food could be contaminated by fumes (exhaust or fuel) hence thinking about using an inverter... the bloke himself was talking about just dangling a pipe for the exhaust out the window with the genny on the passenger seat !

I think you'd be much better off with a 240v generator. That's quite a hefty load, and the inverter will lose a fair bit in conversion.

Is he completely mad or just in need of help?

Apart from the risk of setting the seat on fire in normal use what does he imagine would happen if he had to brake suddenly?

Why not use hot boxes as used by meals on wheels and the old school meal delivery service

Tony

If it's whilst he's driving then the alternator will run it, assuming it's insulated it won't pull 700W continously anyway.

You could uprate the vans battery capacity however with the load you intend to pull you are likely to need to increase the alternator output as well , may be a better option to go down the liesure battery route these can be deep cycled where ordinary vehicle bateries cant

There is another option , draw heat from the engine , via the cooling system

I have yet to see a simngle burger van that's not on gas or uses a gennie.

A large one will be approx 70 amp/hr. At the 20 hour rate. Ie discharged at 3.5 amps. Discharge it at a greater rate and the capacity will be less.

You'd need several large leisure batteries connected in parallel for this task - and probably better to go to 24 volts, so series parallel. Four should do it. About 100 quid each. The invertor will be expensive (about another 100 quid) as will a suitable charger. You're way outside mass produced domestic units here.

All batteries are marked in amp/hours.

But what you really need is a portable generator. Far cheaper and more reliable. Or just for heating, Calor gas. Check out how a mobile food stall does things. They just don't use batteries for anything.

I've seen quite a few that run on a genny, one on Empire way not 15 minutes ago.

I wouldn't recommend putting batteries in parallel for any length of time.

Better not buy a truck then. Lead Acid batterys are perfectly happy in parallel.

Why's that then?

That`s basically what he's trying to accomplish - any ideas how they used to heat them ?

Correct, assuming you can find such an inverter at a reasonable cost. I've got a basic 350W one which was cheap so it's not that demanding a spec. They have to be pretty efficent because any power loss in the device gets dissipated as heat in the components and if it's much then they'd burn themselves out.

60Ah is a ballpark figure, however they never actually achieve that while maintaining close to 12V terminal voltage, it's pretty much a theoretical figure, you'd be lucky to get 30Ah out of a 60Ah rated battery in this application while still running the inverter. Hence you might expect it to power your food warmer for half an hour. You'd need about six batteries for your three hour window. This is all very finger in the air by the way. Like I said elsewhere, don't consider running a bunch of them in parallel in this application.

So go for bloody well insulated boxes and a lower power heat source? All you have to do to maintain temperature is pump in enough power to match whatever's being lost out of the containment at that particular temperature. Reduce your heat losses and you reduce the power input you need.

Not in this application, where they're being steadily discharged and not receiving charging at the same time. I can't remember why, I'd have to ask my tame battery expert in work. Admittedly you'd probably get away with it if they were all the same make and model from the same batch and with the same life history as then any imbalances in energy capacity and density will be negligible.

I think you'll find they're actually in series - that's why lorries are

24V.

Not to point out the slightly important fact that lorry batteries are wired in series.

Lead acid will work fine in parallel for this sort of app. It's not recommended to parallel Ni-Cads due to different characteristics. But again you can assuming you're not looking for them to hold their charge over an extended period.