Flash Recylcing with External Power Supply

[Mando327]

Hello Guys,

I have the Canon 20D with the 580EX speedlite and the CP-E3 Compact Battery Pack. On the custom functions it gives you the ability to: Recycle with both the Speedlite and external power source, or recycle with only the external power source. It also says "If both the external power source and the speedlite's internal batteries are used to recharge the flash, both were sources will be used together. However, if the internal batteries become exhausted, shooting may be disabled. If 1 is set, only the external were source will be used to recharge the flash and the internal batteries will be spared. Note that even if you set it to 1, the speedlite will still require internal batteries for flash control."

My question is if both sources are used to for the recycling of the flash, do BOTH sources become exhausted at the same time (battery pack and speedlight batteries)? Or not necessarily? Do any one of you guys prefer one or the other, and why? And if i choose both for recycling and the Speedlite's batteries become exhausted first, do you have to change the batteries in both the Speedlight AND the battery pack? I think they mention to put batteries of same type and charge, but does that mean for just the speedlight, or speedlight AND the battery pack, even if the battery pack is not completely exhausted?

Thanks Guys,

Armando

[EmbeddedMatt]

"[D]o BOTH sources become exhausted at the same time?"

Doubtful.

"And if i choose both for recycling and the Speedlite's batteries become exhausted first, do you have to change the batteries in both the Speedlight AND the battery pack?"

Doubtful.

"I think they mention to put batteries of same type and charge, but does that mean for just the speedlight, or speedlight AND the battery pack, even if the battery pack is not completely exhausted?"

Just the speedlight. Don't mix battery types and charge within the speedlight or within the battery pack but it's hard to see why you would need to keep the speedlight and battery pack "matched" so to speak.

The caveat here is that I am answering as an electrical engineer but without knowledge of your specific equipment. So you should consider this an educated guess.

[another view]

Looks just like the Nikon unit I've got, except the Nikon holds six AA's (plus the four in the flash). I can tell you that with 2100mah NIMH rechargeable batteries in both (and a full charge), 300+ shots are no problem. And no recycle time even at the end of the night. Literally, it's ready instantly after it fires. At that rate, I have absolutley no idea how many more shots it can handle - I'd be tired out before the batteries!

Depends on your use though - I'm using different equipment set at ISO400, f5.6. Also, short flash-to-subject distance at wedding receptions, so I'm not really hitting the flash that hard.

[Clemmie]

"["I think they mention to put batteries of same type and charge, but does that mean for just the speedlight, or speedlight AND the battery pack, even if the battery pack is not completely exhausted?"

Just the speedlight. Don't mix battery types and charge within the speedlight or within the battery pack but it's hard to see why you would need to keep the speedlight and battery pack "matched" so to speak.
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Actually......it makes sense to me, that you would want matched batteries in both units.

It seems logical to me, that the two sets of batteries are interconnected in such a way, as to provide a set voltage - but with the combined amperage and reserve capacity of both sets. If one set goes dead before the other, with all interconnected, it can cause serious problems.

Comparable example: the three battery setup on my Freightliner. (Stay with me a moment - and you'll see the potential problem).

This is a 12-volt system, in which three large 12-volt batteries are parallel-wired, to provide 12-volts with about 300 ampere-hours storage. (This is the same way that the two sets on your flash setup interact). These batteries are replenished by a 140 ampere-hour alternator, and the peak draw on the system (aside from the moment of Starting, which draws 'all available power') can reach a 200 ampere-hour rate at times, when all systems are at maximum draw.

I know from expensive and painful experience, that if one of these batteries fails unexpectedly, it can wreak havoc on the entire system. The alternator is placed in a peak load situation, trying to compensate for the dead battery - and a sudden additional load, such as switching on the lights as it gets dark, can overload it and burn it out in just a minute or two. Which then results in a high discharge load (which causes Heat) on the two remaining good batteries - and by the time I can reach the repair shop (which better be within the hour, in this situation) they are also 'toast'. (For the curious - three truck batteries, a Leece-Neville alternator, and the hour of labor to switch them out, runs on the high side of $800 - which can really screw up one's operating budget for the month.)

Now, on your flash setup, I doubt that one set failing before the other would prove as dramatic, or as expensive, as my example - but the same principles apply. With two or more batteries interconnected, power will flow from the stronger to the weaker until they equalize - or until the stronger one dies, likely from heat buildup, while trying to recharge the weak or dead one.

So, in interconnecting two mismatched sets, you set up TWO battery-killing situations: 1. On the freshly-charged side of the day, as the batteries attempt to 'equalize' with each other, you get an overcharge situation on the lower-rated set....and 2. On the other end of the day, as the weaker set is exhausted, you get heat buildup from accelerated discharge on the stronger set, as they attempt to 'equalize' against the dead set.

Hopefully you'll understand now, the necessity of keeping the ratings and charge rates matched up in an interconnected system. And if not, then just trust me - this is the way batteries work in the real world.