240 volt rechargable power pack?

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I need to find a rechargeable power pack to run power tools from, where no mains supply is available. Does anyone know who sells such a thing?
Thanks
Jack
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On Mon, 20 Oct 2003 10:46:24 GMT, snipped-for-privacy@yahoo.com (Jac) wrote:
PS.. It needs to be small and portable...
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Jac wrote:

They're called generators :-)
Seriously - if you need any amount of power (more than a couple of hundred Watts) for any period of time (more than 10 minutes), a generator is your only option.
--
Grunff


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Thanks for the reply. Actually, I only need to run 25 watts, and the power needs to last about 2 hours max... A generator would be unsuitable because of the location/working environment.
So... still looking for a 240v rechargable power supply...
Jac
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Jac wrote:

That's very easy - 1x car battery, 1x 12V inverter.
--
Grunff


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Grunff wrote:

Like maplin.co.uk code N32AZ
Out of interest, what 25W device do you need to run which is only available in a mains version?
--
Grunff


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Actually a small 25w solid state guitar amplifier. (a "tool" of my trade)...
Jac
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snipped-for-privacy@yahoo.com (Jac) writes:

Are you the bloke who busks in Canary Wharf Tube Station in the mornings?
If so, can you learn some new tunes, please?
--
"The road to Paradise is through Intercourse."
The uk.transport FAQ; http://www.huge.org.uk/transport/FAQ.html
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On 20 Oct 2003 14:56:33 GMT, snipped-for-privacy@ukmisc.org.uk (Huge) wrote:

You are quite safe... The last time I did any busking was in 1979.... :-)
Jac
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Jac wrote:

That is going to be running on a much lower voltage than mains, DC too - so it wouldn't make sense to carry around a 12V battery, step up the voltage to 240AC, feed it into the amp which then steps it back down to probably 12V, maybe as much as 24V.
The most sensible thing to do is find out what voltage it runs at (if you're not confident opening it up and investigating, find someone who is) and use a car battery/two car batteries depending on the voltage.
--
Grunff


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Grunff, Thanks for the continued suggestions. It actually runs on 14volts after the mains transformer. I was initially trying to figure out how to add a rechargeable battery to the cirquit, but it's not as simple as it sounds because there is a split power supply: a positive one and a negative one, so it would require two batteries. Large echargeable batteries aren't cheap and I don't quite feel competent enough to mess around with the cirquit. But I guess I could possibly employ a tekkie to do thie job, if I can find one who knows what he's doing.
So, still looking for ideas..
Jac
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Jac wrote:

If it runs on 14, it'll run on 12. You can either use a negative voltage generator, or much more simply, use two batteries.
You say rechargeables are expensive - go to a motor factor (not Halfords!), and buy two of the smallest car batteries they have. Mini (as in Austin) batteries are great. Should be about 20 each.
Make up a suitable box for carring them, and you're off. That provides you with your +/- 12V, and enough capacity to play all day.
If that's too heavy (I don't know how far you intend to carry this), get a pair of 12V sealed lead acids - but you really need at least 10Ah for this to be useful.

With a pair of batteries it's 3 wires, that's it. Much simpler than using a mains inverter.
--
Grunff


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Grunff wrote:

24 SUB C Nicads 1700Ma/h would weigh 3lb roughly, and sit in the bottom of the case. Dead easy to source in backs of 6. at 25W - about 1-2A drain - gettng on for an hour of playing at least. More money would net you larger capacity cells too.
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AA size NiMH are at least 1800mAh these days, smaller and lighter than C size and no Cadmium to get back into the environment when the cells peg out.
I recently bought about a dozen 1800s for a tenner (Maplin IIRC). With a supply providing 180mA (C10 rate) to charge them they should completely recharge in 14 hours and won't cook if you leave them on longer. With a bit of luck the amp's built-in power supply should be capable of supplying the charging curent, so it should be a matter of just getting someone to wire in a couple of resistors and install the batteries in holders (which you can probably do yourself if you can solder at all) and presto! you've got an amp that runs seamlessley off mains or its own internal batteries. (You'll probably also need to modify or add an on/off switch to switch off the supply from the battery to the amp whilst leaving the mains on for charging.)
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John Stumbles wrote:

Yes, but I was talking about a cell that is cheaper, lasts longer, and can deliver more power. NiMh have lower current capacity, self discharge badly, have limited life, and are expensive.
Weight is not an issue with a 25W guitar amplifier.

I think thats peretty much exactly what I said...

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12 * 1700mAh 'C' size NiCds for 10? (Maybe - haven't looked)

as in number of recharge cycles? Manufacturers seem to be quoting up to 1000 cycles, as per NiCd.

so I'm probably still better off with NiCds for my cordless trim saw, and you for your electric aeroplanes, but if the OP is going to drain his batteries that quickly he's probably playing with Hotblack Desiato ;-)

Depends whether he's keeping them charged before use, doesn't it?
The size might be an issue if he's trying to build the battery pack into an existing amp case.
And all other things being equal I'd prefer not to encourage more toxic chemicals to be introduced into the environment. Others may differ :-)
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Although *slight* overcharging (say an hour or so) shouldn't harm at the C10 rate, long periods will.

It's pretty simple to make a constant current charger assuming you already have the DC supply, so I'd not recommend just using a resistor - after all this is likely to have heavy use so battery life would be important. And NiMH require a slightly more sophisticated charger than Ni-Cads.
--
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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"Grunff" wrote | Jac wrote: | > Thanks for the continued suggestions. It actually runs on 14volts | > after the mains transformer | If it runs on 14, it'll run on 12. You can either use a negative | voltage generator, or much more simply, use two batteries.
Also much safer from a public liability viewpoint to have only battery voltage supply rather than 240V ac floating about. But make sure the battery leads are fused as if they are accidentally shortcircuited Nasty Things Will Happen.
Owain
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Jac wrote:

+- 14v? and a split rail? That's easy - 2x12 cell Nicad pack.
Not hard to modify either. Need to turn the original transformer into a trickle charge circuit (couple of resistors) , and replace the AC switch with a DC one, running off the cells.
Trivial really. However the cells won't be cheap. Your best bet is to source 4x6 cell packs as used in model car racing, and use those - iften available on E-bay cheep, cos ebveryine wanst more powe than those toys come with, and upgrades.
If you are in east anglia, I'll have a go modding it.

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input for you. It would probably run happily off a small burglar alarm type lead acid battery, never mind a car battery.
--
Tim Mitchell

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