Hi Steve
The Type of Battery and Firing rate is what causes the overheating in the SB-900
Here is a link that explains it with movies , you may what to mute music.









Lou Recine

I know I haven't been able to use lithium batteries in the Canon 580 because it overheats, but in my smaller nikon flashes lithium is fine. I think it's a matter of testing flashes with each kind of batteries and then just buying bulk of the batteries that work best!

Lou, Shannon. Thank you both. I watched the You Tube movies (without sound,see what you mean! lol) and will experiment with batteries a bit more. It may be a one off but from a confidence viewpoint I think I will invest in a SD9 pack at some stage very soon.

Hi Kallarian
I have one my self , expensive but at the same time indispensable.
It will save you a tonne of post processing , flash exposure is a lot more even
I don't have the problem of one image good then the next image dark.

Also Recycling time is really improved and I can normally do a whole wedding with 12 batteries 4 in camera 8 in SD-9 in problem.
I keep the SD-9 in my pocket so I can quickly unclip and I have a holder on my light stand so its easily transferable.

and the best part.......... When the batteries wear out ( and they will wear out ) I just go my local shop and pick up brand new NiMh batteries ( no down time )

Also I forgot to mention the warning beep on the SB-900 can be turned off , because it turn out it's becomes very loud in a church , and for some reasons even louder in a catholic ceremony ( go figure ) LOL.

Lou

Maaan, I wish those video clips were text I could read instead.
They are 7:30 minute video clips that would take a fraction of the time to read.

Regardless .. thanks for posting! Solid info there.

I use Duracell and Energizer batteries and my SB-900 still overheats and when I take the batteries out they are red hot....I have learned to work with two SB-900's for when one overheats....Anthony

I've been lucky re my 900s, not a problem.

What I am using: The Battery Pack + Flash all loaded with Sanyo Eneloops.

But I do keep my frame rate down, in short 2-5 frame bursts, then around 3-5 seconds pause, just seems to work out that way. I have never seen the temp indicator climb yet.

I will say this ... I've burnt out SB-900 and SB-800 and 580 EX and 580 EX II speedlights. They will all go melty if you work them too hard. It's not just the SB-900 (which unfortunately has gotten a bad rep about this.)

http://neilvn.com/tangents/2008/11/28/nikon-sb-900-thermal-cut-out/

I know this is a late reply but hopefully it helps a bit.

Flash tubes and power. These little nukes put out a lot of juice in a very short time. Any resistance to the transmission of that power translates into heat. Gels, front freznel, cheap battery construction, you name it and it's got resistance.

The front freznel of the flash falls victim. Plastic clouds up as it ages or gets dirty and that extra resistance to light transmission starts heating up significantly and then we see the freznel going all bubbly in those pics (but luckily they can be replaced) or you have a gel that seems to have fused itself to the front lens. Slight cloudiness can be polished out (with polishing toothpaste I've heard???) or the fresnel replaced relatively cheaply so don't think a bubbled front lens is fatal.

Ditto for batteries. Do you have a particular set of batteries that heats up in the charger? Battery internal resistance is a parasite for the fast flow of current needed to quick charge or discharge a battery. If it heats up charging, it'll heat up discharging and contribute to the heat inside your speedlight. Even if it's just one cell out of 4, the resistance of one will kill recycle times because of lower current and voltage left available to the capacitor charging circuit.

I have purchased one set of every NiMH cell I've ever come across and have seen drastic differences in their thermal characteristics during charging. Equal comparison is tough during discharge since we all tend to run around and so the cells wouldn't get an fair chance but the internal resistance is the same for discharge as it is during charging. So far high capacity Duracells (>2500mAh) are the WORST I've seen and can bleed power through internal resistance almost as fast as a quick charger can push it it....never finishes charging and is practically untouchable with bare hands. The same heating is present when the cells are discharged....not good if you're trying to keep the heat from building up in a speedlight! Honestly I think my happy place is around 2300mAh. It's nice to have a bit of capacity but the higher capacity cells seem to be the ones that heat the most in general. My absolute fav's (never been more than luke warm if memory serves) are some 2000mAh and 2500mAh Sony cells.

Offloading your batteries to a 8cell pack moves this heat source somewhere else other than inside your speedlight (a plus for bigger speedlights with an auxiliary power pack option). I took one 'dumb' speedlight and looked at trying to add a heat sync but it would be nice if higher power lights had some form of thermal PREVENTION in the design instead of just a saftey shutoff.

Thank you for the solid info in that post!