AF 400FTZ and NiMH batteries


sperger2003

Link Posted 07/03/2004 - 11:24
Does anybody know if the NiMH batteries can be used with the AF400 FTZ flash?

I bought one the other day and downloaded the manual which only mentions Ni-Cd and Alkaline batteries. I don't know if this is just because they were the only choices in the mid eighties when the flash was made or whether NiMH batteries would be too powerful or incompatible in some other way.

I woould be grateful for any info.

Carl

MattMatic

Link Posted 07/03/2004 - 20:14
Carl,

You're right about the age. If NiCads are okay, then NiMHs should be fine. I use them in the AF360FGZ and they work a treat I use 2200mAh which seem to just run on and on and on with a fabulously fast cycle time.

The only thing to be aware is the higher capacity NiMHs can obviously deliver a real whack of current, which can add up to quite a bit of heat.

What you try is up to you, but I wouldn't give it a second thought if I had an AF400FTZ flash. Perhaps someone here on the board actually uses NiMHs (especially the ones in the 2000mAh region) who could comment

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

sperger2003

Link Posted 07/03/2004 - 21:46
Thanks Matt

I'll give them a try. I just didn't know whether the NiMH being so much more powerful than Ni-CD might fry the flash-guns circuitry. I'll just take it easy at first, see how I go on.

carl

George Lazarette

Link Posted 09/03/2004 - 23:55
They are only more powerful in the sense of having greater storage capacity. Their voltage is just the usual nominal 1.5 volts so they can't fry your flashgun, just as a 6 volt motorbike battery wouldn't (as long as you used one, not four!).
I have an AF400FTZ and use NIMHs. They haven't fried it yet!

MattMatic

Link Posted 10/03/2004 - 06:46
George,

It could only have been a problem in the sense that the extra current can produce more heat. And, some designs can't cope with the extra current, the design expecting a maximum current given by standard NiCads. Generally, though, such a design is not a good one Most flashguns are designed well enough to cope with high surge currents.

Thanks for confirming things though
Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

George Lazarette

Link Posted 10/03/2004 - 18:50
It's a long time since I did Physics, so perhaps I'm missing something, but I don't see how NIMHs are going to produce more current, except under conditions of such heavy use that other batteries have started to give up the ghost while the NIMHs continue to plough on. Then, the NIMHs would still be producing the normal current, while the other batteries would no longer have the power to do so.
It is I suppose possible that the gun is not designed for continous flashing, (sort of testing to destruction) and that only with high-capacity NIMHs would you be able to create such a situation.
If that is a worry, then the answer is not to use the gun in that way - which in normal circumstances one wouldn't. Or I wouldn't!
Please correct me if I'm wrong.

MattMatic

Link Posted 10/03/2004 - 21:20
George,

Hmmm. Well, the concern was down to internal resistance of the cell. I understood that NiMH had a lower internal resistance, compared to NiCAD. The lower the internal resistance, the more current the cell can deliver... and consequently, more heat too.

However, I got it wrong. Actually, NiCADs have a lower internal resistance than NiMHs. But NiMHs can deliver the current for longer (generally being of a higher capacity, in mAh).

There's a great, and very complex, guide: http://www.buchmann.ca/part1.asp - well worth a look over.

Matt
http://www.mattmatic.co.uk
(For gallery, tips and links)

George Lazarette

Link Posted 11/03/2004 - 00:14
Thanks for that link. I've saved it for when I've got a few free minutes.

I take your point about internal resistance of the batteries, but a properly designed gun should not allow higher currents than it can safely handle whatever the internal resistance of the power source.

The price Pentax charge for these guns, I would hope they design them properly.

Anonymous

Link Posted 04/04/2004 - 13:51
Yes I am glad that you found out that Ni cads have the potential to supply the more current in a short circuit situation, the make up of the batteries means that Ni-cads can supply up to about 90 Amps , this alows for flash guns to cycle quicker , this is the reson many flash guns recomend Ni Cads, NiMh can have a larger energy store , so it's horses for courses , If you use a power winder and want the flash to go off 4 or more times a second then nicads almost certenly your only option , if you want to take many shoots with some tiem inbetween then NiMh will mean less battery changes ,

Maybe one day we will have the best of both worlds,

Kim C

Link Posted 21/04/2004 - 09:20
Hi Carl,
I use 1300 and 1700Mah NiMH cells in my AF400FTZ with no problems. I haven't tried the new ultra hi power ones (ie 2200) but I can't see these being a problem.

As far as internal resistance and current is concerned I wouldn't worry too much about flash guns. The Metz guns are designed to work with Wet Cells This have a much lower resistance and why you can weld with car batts! The AF400T could take a 510v laminated power pack which gives a 2 sec instead of a 6 sec charge rate. NiMH are not going to get anyway near these charge rates. The overall current depends on the total resistance of the circuit. In the case of a short circuit this would be the resistance of the battery plus wire. The thinner the wire the more resistance. Flashguns work on a high voltage, in the order of hundreds. The high voltage is generated by an electronic circuit hence the buzzing as the gun charges. The resistance of this is going to be far higher than the internal resistance of the battery and is going to be the deciding factor. In the case of the AF400T TR packs, normal cells give 7 Secs. NiCds 6 and the 510v pack 2. The difference in the internal resistance of dry cells and Nicd is much greater than NiCd and NiMH so the difference is going to be much less. The 2 sec charge rate is due to the 510V! Low drain applications tend not to like rechargeable because the voltage is so much lower and the the drain is so low that there is little voltage drop and why some say rechargeables are not suitable.

As far as NiCd's are concerned, I have more or less given up on them. Theorecticaly, they can give a shorter recycling time but I haven't noticed a difference, they don't last as long, have a lower capacity and hold a memory!. The only thing I use the NiCd's for now is to replace the battery modules in the motor drive power packs. This isn't because of the effect that the battery has on the drive but rather because the circuitry in the charge pack M isn't designed for NiMh and this could be a problem. I spoke to a firm that specialising in building and replacing Batt packs for just about everything. They tend to replace NiCds with NiMH whenever they can ie same size equivalents. Apart from the capacities, they is very little difference in the discharge characteristics of the 2 types. The only real problem is on the charge cycle and this can be very different and their advice is not to use a NiCd charger on NiMHs and not to put NiCds in a NiMH charger unless it says you can.
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