Power requirements of studio strobes

Thanks, Longwatcher. Based on your info I'll quit worrying about this issue. If/when I get the lights, I might get out my clamp-on amp meter and take some readings to satisfy my curiosity.

Curtis N wrote in post #2615289
Thanks, Longwatcher. Based on your info I'll quit worrying about this issue. If/when I get the lights, I might get out my clamp-on amp meter and take some readings to satisfy my curiosity.

Hi Curtis,
I thought about that too, but I think the speed of the surge might make it difficult to measure. It might be the reason it doesn't trip the circuit breaker. I wonder how many it would take to do that?
Dan

Curtis N wrote in post #2615289
Thanks, Longwatcher. Based on your info I'll quit worrying about this issue. If/when I get the lights, I might get out my clamp-on amp meter and take some readings to satisfy my curiosity.

I would suggest also looking at the line voltage on an oscilloscope and figure out how much it dips during the recycle time. That would be the most important factor even if a breaker does not trip. The circuitry in the flash unit may not like low voltage on the supply side.

SkipD wrote in post #2616503
I would suggest also looking at the line voltage on an oscilloscope and figure out how much it dips during the recycle time. That would be the most important factor even if a breaker does not trip. The circuitry in the flash unit may not like low voltage on the supply side.

Hi Skip,
When this discussion started I was puzzled how the Vagabond could power up to 10 lights. The Vagabond seems to be a current limited device. As the number of lights is increased, the voltage does drop (they say similar to a brown-out) and just increases the charging time. They say that their lights are designed to handle the lower voltage and not to use other manufacturers units.

I guess we need to find someone with 4, 5, or ? of the AB's to do a test! Actually I just emailed them and I will post their reponse.
Dan

ToyTrains wrote in post #2616709
I guess we need to find someone with 4, 5, or ? of the AB's to do a test! Actually I just emailed them and I will post their reponse.
Dan

Sounds interesting. Please let me know the details of their reply.

I have four AB units - two B800's and two B1600's and could run some sort of test here. I have oscilloscopes and clamp-on current meters as well as a shunt that I can measure the electrical activity with. I'd rather have the info from AB before running any risk, though.

I have 6 AB strobes, but don't have the equipment (other then an outlet and circuit breaker) to test all six at once. I really would not feel comfortable delibrately trying to trip a circuit, given the age of my house. The circuit box is new, the wiring is mostly not.

SkipD wrote in post #2616755
Sounds interesting. Please let me know the details of their reply.

"The Bees are rated at about 8 amps and could possible
peak at 18 amps at the initial stages of recycle if you are using the model
lamps on full, but this is for such a quick instance will not cause a
problem. You can safely plug 2 of the B800's into a 15 amp breaker and
should not have a problem...you would probably not run into a problem even using 3."

Curtis N wrote in post #2615289
If/when I get the lights, I might get out my clamp-on amp meter and take some readings to satisfy my curiosity.

Keeping a nine-month-old promise, my B1600 units arrived today and I got out the clamp-on meter.

Running them both through the same cord, at full power the amperage would gradually rise and fall throughout the 2 second recycle, peaking at around 12.3 amps about halfway into the cycle (about 6.2 amps per unit). It's a digital meter that updates the reading about three times per second and it's possible the current peaks higher than 12.3 between readings.

Backing down to 1/2 and 1/4 power, the current would still peak around 12.3 amps but the peak would come earlier with the faster recycle, still about halfway through the process.

At 1/8 power it would peak still more quickly. Readings reached only 9 or 10 amps but the actual spike might be too quick for the meter to register.

From this analysis I would assume that three units would be no problem for a 20 amp circuit and probably not give any trouble to a 15 amp circuit as long as the fuse or breaker has a bit of a time delay (I believe most do). Four units would probably not bother a 20 amp circuit, which concurs with earlier testimony in this thread.

As an aside, the B1600 units at 1/16 power were able to keep up with the 5 fps burst of my 20D and give consistent exposure through six frames. This might be more taxing to the power source, creating higher average current draw throughout the burst.

Curtis,
If I recall correctly, a single unit rated to work on a 15A household circuit should be no more than 13.5A steady draw...for example, ever notice how 1500W is the most that hair driers, toasters, microwave ovens, and a host of other household appliances, or 110v * 13.5A = 1485W. I forget what an acceptable brief surge time duration and voltage spike is acceptable on the same circuit. I'll see if I can find that info, I just can't recall what I learned over 10 years ago and didn't use since then!

Wilt wrote in post #4223226
Curtis,
If I recall correctly, a single unit rated to work on a 15A household circuit should be no more than 13.5A steady draw...for example, ever notice how 1500W is the most that hair driers, toasters, microwave ovens, and a host of other household appliances, or 110v * 13.5A = 1485W. I forget what an acceptable brief surge time duration and voltage spike is acceptable on the same circuit. I'll see if I can find that info, I just can't recall what I learned over 10 years ago and didn't use since then!

Circuit breakers and how they respond to varying loads is complex. Think of a cicuit breaker as a thermal bi-metallic strip that will trip when the heat generated within it causes the strip to bend "enough". This depends upon the amount of current drawn and the amount of time. If the current draw varies, like in a charging flash, it is difficult to know when it will be sufficient to cause the breaker to trip.

For brief periods you can supply substantial overcurrent without tripping a breaker. This is by design and allows a higher current startup motor, for example, to briefly exceed the breaker rated current. Some breakers are designed to break much more quickly to protect certain equipment.

As it takes some time for a breaker to internally cool, the amount of time between flashes will also have an effect (meaning decreasing the time between flashes, will allow higher loads).

Am I glad that in the UK we use a 32 amp breaker on a "ring main" - never had a problem with overload tripping using my Elinchroms.