Inverters - a health warning!

[Martin]

- people are now buying cheap mains inverters for use when away from home, powered either by their car or van battery, so they can run "mains" accessories.
Many retailers are grossly overselling them, claiming they can do the impossible and bringing about dreadful cruelty to innocent batteries!
Sorry, its sums time! - the average car battery is something like 50 amp/hrs capacity, so at rest, it should be able to sustain up to a 5 amp constant discharge - that's 60 watts........so nearly all inverters (which tend to start around 75w) are draining rather a lot of current (above that recommended for constant discharge rate) for a start. I came across someone who's been sold a 1kw inverter for use in his motor home, and the salespeople had suggested he could use it to run his hairdryer...........
When I did the sums, it would be highly likely that if he tried it on his single battery that it may last for a couple of minutes before the voltage would plummet to a level below which the inverter would cut out, and the enormous discharge rate may well cause permanent battery damage
SO, inverters can be very useful, but if you're going to run it off a motor or leisure battery, don't buy too large - a simple rule of thumb would be
"aim to have the inverter wattage somewhat around the amperage of the battery" - (ie, if you have a 100 amp hr battery, an inverter of around 100-150w will be ok)
I'm tempted to set up a "be kind to your battery" website!

[wulf]

Am I right in thinking that there is another kind of battery that is more suitable for use with inverters? I remember talking to someone a few years back about running a bass amp from a battery and vaguely recall him mentioning that he didn't use his car battery but a (?)marine one instead.

Wulf

[Martin]

car batteries really aren't up to the job, they just aren't designed for deep discharge, and will have a very short life if deeply drained (not just for inverters). For music away from the mains, I'd probably go for something like "AGM" (advanced glass mat) batteries which have true deep-cycle capabilities (around 300 cycles to 80% depth of discharge) - guide price, around £75-£90 for 100 amp/hrs

[Wombat]

Yep good point!

doen't matter what you are told or believe.............the physics will get you every time!

Nev

[mrsflibble]

and bear in mind a little car factoid: many modern (by that I mean the last 15 years or so) cars will have alarms and immobolisers which, if the battery gets discharged by something like an inverter, it will set off the alarm and immobolise the car.



my hubby's stepdad's car alarm kept going off recently. hubby took a look and found an amplifier running off an inverter which had been draining the battery to buggery.