Capacitive battery charger

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hat27533
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Location: Cambridge, England
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Capacitive battery charger

Postby hat27533 » Mon Jan 12, 2009 7:57 pm

Anyone have any experience in using Capacitive chargers for their ev?

Something like this http://e-volks.com/capacith_charger.html :?:

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Jeremy
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Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Mon Jan 12, 2009 8:44 pm

That certainly looks like a scary bit of kit!

No isolation from the mains, so the battery is potentially sitting at mains voltage levels and near constant current charging, which will cause any lead acid technology battery to seriously over-charge if left on for long periods.

I never cease to be amazed at some of the truly inventive ways people can come up with to put their lives at risk.

Although charging high voltage batteries will always carry some risk, my view is that it's best to minimise this as much as possible. Isolation between the mains supply and the battery terminals, using a decent isolation transformer, is a must, as it reduces the accidental shock risk (if the supply is isolated, then you can't get a shock from just touching one terminal whilst standing on the ground).

Jeremy

ChrisBarron
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Joined: Tue Dec 11, 2007 11:26 pm

Postby ChrisBarron » Mon Jan 12, 2009 8:53 pm

Jeremy wrote:That certainly looks like a scary bit of kit!

No isolation from the mains, so the battery is potentially sitting at mains voltage levels and near constant current charging, which will cause any lead acid technology battery to seriously over-charge if left on for long periods.

I never cease to be amazed at some of the truly inventive ways people can come up with to put their lives at risk.

Although charging high voltage batteries will always carry some risk, my view is that it's best to minimise this as much as possible. Isolation between the mains supply and the battery terminals, using a decent isolation transformer, is a must, as it reduces the accidental shock risk (if the supply is isolated, then you can't get a shock from just touching one terminal whilst standing on the ground).

Jeremy


Lol...it looks as if they've gone round the kitchen looking for things to use.....
"oohhh get the bread bin, that'll be handy. And whip the handle off the cupboard door too"
Thank goodness there's no plantpots or pot pouri involved !

Seriously though, I am curious about it's operation even just from the point of view of high efficiency. Any idea where I might find a circuit explanation because it's pretty new ground for me.

hat27533
Posts: 16
Joined: Sat Sep 27, 2008 6:41 pm
Location: Cambridge, England
Contact:

Postby hat27533 » Mon Jan 12, 2009 9:25 pm

Tee hee, the handles missing from the loo door too !

They are actually selling these on-line.

I did an electrical apprenticeship and also worked at The Post Office Research and Technology Centre so understand the dangers. I write software these days though.


I wasn't thinking of buying one, was intrigued to see if anyone was using the technology here and if it works.

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Jeremy
Posts: 472
Joined: Thu Jul 31, 2008 6:35 pm
Location: Salisbury

Postby Jeremy » Mon Jan 12, 2009 9:31 pm

If you put a capacitor in series with an AC supply (in this case 110V, 60Hz) then it will effectively act as a current limiter. It acts a bit like a series resistor, but without the high losses, as it uses reactance, rather than resistance, to limit current. The current it will pass is determined by the reactance of the capacitor (a function of supply frequency and the capacitor value), plus the resistance of the load it's feeding. Before feeding the battery, a rectifier is needed to turn the AC into DC.

The snags are many and varied. The obvious ones I've mentioned; no isolation from the mains and no voltage limiting at end of charge. Other snags are that the capacitor needs to be rated for the peak supply voltage, which means around 400V for the UK, plus it has to be a quite large value to pass a reasonably high current. Both of these factors tend to make the capacitor a bit expensive for use on our higher mains supply.

Jeremy


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