----- Original Message -----
> Date: Mon, 10 Feb 2003 06:01:53 -0600
> From: "Curtis P. Hedman" <Curtis.P.Hedman-1@xxxxxxxxxx>
> Subject: [OM] NiMH in T18?
>
> Maybe an old question (I've searched the archives w/o success) -- The
> instruction sheet with my new (to me) T18 indicate that NiCd batteries
> should not be used... how about NiMH? And, by the way, why NOT NiCds? Is
it
> the lower voltage, too much current, ??? I'm pretty happy with NiMHs in my
> T32 and T20...
>
> Thanx,
>
> Curt
I asked this question in a thread about six months ago. Tim Hughes gave the
answer. NiCd and NiMH batteries have a lower internal resistance than
alkaline. As a result, when the flash charges, higher currents flow in the
flashgun's circuitry. The T20 and T32 have circuits designed to survive
this higher current, but the T18 does not. So using NiCd or NiMH batteries
in a T18 may burn out the circuit immediately, or significantly reduce its
working life.
Tim Hughes suggested an answer -- put a small resistor in series with the
batteries. The idea is that the resistor plus NiCd/NiMH battery should have
a combined resistance roughly equal to that of an alkaline battery. Tim
suggested a resistance of 0.25 ohms for the two-cell T18. Of course, a
series resistance will reduce the charging current, and hence the flashgun
will take slightly longer to charge, but at least you will be able to use
NiCd or NiMH. Ideally, you want the extra resistance only when you have
NiCd or NiMH installed, so a permanent modification to your T18 may not be
such a good idea.
I have a T18 myself, but I have not tried this resistor trick (yet). I like
the T18 for on-camera use better than the similar-power T20, as the T18 puts
the flash tube further away from the camera lens, reducing the chance of
red-eye. Note: the T18 is either manual or TTL auto -- it has no sensor of
its own to do flash-controlled auto.
-- from Cy in the UK
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