Charging NiMH cells from a hub dynamo

Ambrose Nankivell

In news:c563u0d248cmno1jg6da3gng68ocsigi4k@4ax.com,
Richard Bates <usenet01@artybee.net> typed:
> On 9 Jan 2005 17:33:36 GMT, Mark Thompson
> <pleasegivegenerously@warmmail.com> wrote:
>
>> If he wants it for touring, could he not just take it off charge
>> when 'stop starting', and whack it back on charge when doing a
>> steady speed for hours on end?
>
> Good idea, but not my style of touring! I take the kitchen sink when I
> cyclecamp, and even the slightest hill would bring my speed down to a
> pitiful 5mph or less

I suggest a carbon fibre kitchen sink.

Ob on-topic:

I picked up a cheap dynamo set as a gift at the L(to your new job)BS, and
the proprietor insisted I had a look at his hub dynamoes while I was getting
it. Probably wouldn't be much help with esoterica, though. Russell's on
Stafford Street, Walsall is the place, though.

A

James Annan

Toby Douglass wrote:

> With NiMH, the charger detects that the battery is full by monitoring
> the batteries response to the input current; there's a certain behaviour
> exhibited when the battery is charged.

But only with a suficiently smart charger. As others have already said,
a dumb trickle(ish) charge will work well enough in practice, and NiMH
are getting cheaper all the time. So long as the dynamo doesn't really
fry them it should work fine.

James
--
If I have seen further than others, it is
by treading on the toes of giants.
http://www.ne.jp/asahi/julesandjames/home/

Jon Senior

James Annan wrote:
> But only with a suficiently smart charger. As others have already said,
> a dumb trickle(ish) charge will work well enough in practice, and NiMH
> are getting cheaper all the time. So long as the dynamo doesn't really
> fry them it should work fine.

Definitely the best suggestion. Avoid wrapping them up too well
(Exposure to the wind will help keep the temperature low) and then
charge them at something like C/10 (ie. 2000mAh should be charged at
200mA). They'll take a long time to charge, but it's a much simpler
setup than messing around with smart charging.

If you've got the confidence to go down the smart charger route though,
I've got one of the Maxim smart charger ICs (Don't remember which),
which you're more than welcome to.

Jon

David Lowther

"Steven M. Scharf" <scharf.steven@linkearth.net> wrote

<snip>
> > Slightly more complex, you could hook the output of the bridge rectifier
> > to a switching regulator, i.e. Linear Technology LTC1504A - 500mA Low
> > Voltage Step-Down
> > Synchronous Switching Regulator. Set the output voltage to 5V. Then use
> > one of those USB powered AA NiMH chargers.
<snip>
> The Panasonic BQ-830 has the USB input option. Not sure if it is sold in
> the UK though. If you go the route of regulating the output of the dynamo
> down to 5VDC, this would be good charger to use.
<snip>

Bear in mind that most USB devices do nothing useful
without being told what to do by a PC.

Any USB device that functions normally, merely because
it has 5V applied to its input, is a device that seriously violates
the USB standard.

If you can find one then it would be fine for use on the bike
but I wouldn't plug one in to my PC ;-)

This link has some useful info on charging NiMh batteries.
http://www.powerstream.com/NiMH.htm

Dave.

scharf@hotmail.com

David Lowther wrote:

> Bear in mind that most USB devices do nothing useful
> without being told what to do by a PC.
>
> Any USB device that functions normally, merely because
> it has 5V applied to its input, is a device that seriously violates
> the USB standard.

This is not true. The USB standard sets limits for the amount of
current a device can draw, 500mA (though in reality you can't even set
the trip point for over-current to less than 1 amp on any of the USB
controllers I've worked with).

There are probably a hundred different devices that use just the power
from a USB port, with no connection to the data lines. As long as they
don't draw more power than the USB port can supply, it's just fine.

> If you can find one then it would be fine for use on the bike
> but I wouldn't plug one in to my PC ;-)

Whatever. But please don't believe that doing so would have any effect
on your PC at all.

Ian Dobbie

scharf@hotmail.com writes:

> There are probably a hundred different devices that use just the power
> from a USB port, with no connection to the data lines. As long as they
> don't draw more power than the USB port can supply, it's just fine.

Yup, there is even a Phillips electric shaver that you can charge from
a USB port!

>
>> If you can find one then it would be fine for use on the bike
>> but I wouldn't plug one in to my PC ;-)
>
> Whatever. But please don't believe that doing so would have any effect
> on your PC at all.

Except draw power, which may be a major issue for a laptop.

Ian