# Question regarding amperage, voltage, and strobes



## SrBiscuit (Nov 27, 2010)

hey everyone...
hope all your bellies are full from thanksgiving and you all had an enjoyable day. :hug::

so a few weeks ago i was using my studio strobes and one of the fuses blew.
i just got around to going to home depot today to replace it and grab some spares for this situation in the future.
but i ran into a bit of an issue...
so the fuse that was in the lights was marked 5A 250V...with my very limited knowledge of electrical stuff, i determined that it means 5 amps, 250 volts.
am i good so far?:blushing:

home depot had 2 choices...3 amps at 250 volts, or 5 amps at 125 volts.
the person i talked to said that i was in no danger of ruining the lights if i went with either, so i opted for the 3 amp 250 volt fuse. not quite sure why.

i got home and replaced the fuse, and the second i turned the light to the on position (not testing the strobe, just turning it on), the fuse blew again.

im not sure if this is an issue with the strobe itself, or if it's because i chose the wrong fuse. what would be the downside of going with the 5amp 125 volt fuse?...will i just not get full power or will that one blow too?

guess i need to look online for the exact fuse. the guy at HD told me a 5amp 250volt fuse was kind of old, and not that easy to come by anymore.

any thoughts from anyone here? clearly my knowledge of electricals is very shallow, and i could really use a hand. if my picking the 3 amp fuse was totally stupid...lemme know lol...ill try not to cry.

thanks in advance.


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## KmH (Nov 27, 2010)

Hummm...No caps.


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## c.cloudwalker (Nov 27, 2010)

Since you're talking about Thanksgiving, I take it NH means New Hampshire and therefore I am a bit confused.

In the US we use 110v in most of our home circuits with just a few in 220v for things like stove, dryer, etc. So why do the strobe have 250v fuses? Not that is should matter really as what it means is that they will take up to 5A at 250v.

Since it is unlikely that you are getting 250v to them, the problem may be with the amps or there is just something wrong with the circuit. Talk to an electrician is my best advice. I'm not enough of one to help you and most people in hardware stores don't know what they're talking about.

And in the meantime, you may wait to use the lights until you have solved the problem.



EDIT = Actually, you may want to just call the company that makes the strobes.


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## Josh66 (Nov 27, 2010)

I would try to find the right fuse somewhere...

Granted, there's got to be a little margin for error built in, but a difference of 40% (with either fuse) or thereabout is probably pushing it.

If you can't find it locally, I'm sure you can online.

Have you tried Radio Shack?


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## SrBiscuit (Nov 27, 2010)

Sorry Keith...if I recompose the situation with caps would you take a shot at helping me out?

Cloud, I sent the company an email today, so hopefully I'll hear back sooner than later.

Josh, I haven't yet tried the shack. I guess I thought I'd find a more robust selection at the Depot. Color me wrong lol.

I'll head over to the Shack tomorrow and see what they have to say.

Just so I understand...in getting the 3amp fuse, did I get a fuse that would underpower the lights? or with the amperage wrong, will it just not work?

Thanks again.


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## Josh66 (Nov 27, 2010)

Man ... it's been a long time and I don't want to give you the wrong information...
Considering that a 10th of an amp can kill you, and we're talking about 3-5 amps...

All I can say right now is try to find the fuse it calls out for.

Someone, somewhere has it.


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## c.cloudwalker (Nov 27, 2010)

SrBiscuit said:


> Just so I understand...in getting the 3amp fuse, did I get a fuse that would underpower the lights? or with the amperage wrong, will it just not work?



I don't think it's going to underpower the lights but I think it's going to keep blowing. If there's a 5A fuse in there, it must mean that the actual amperage is close (although under) to 5A. And the 3A would not be enough and will keep blowing.

But again, I am not enough of an electrician for you to trust me. I tried calling a electrical engineer friend to ask but there's no answer. Probably getting stuffed on leftover turkey 


Edit = When and if you talk to the manufacturer, don't mention having put a new fuse in there that doesn't match the original... Just in case there's a problem with the light. You don't want them to tell you you caused the problem.

Radio shack is not a bad idea btw. They have a lot of weird stuff like that and you can probably see online if they have that.


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## Vinny (Nov 27, 2010)

You are right in the thinking that 5A 250V = 5 Amps 250 Volts.

To confuse matters, there are slow blow fuses and fast blow fuses. There are letters (AGC, ABC, ...) on them that indicate what they are.

It is always best to under amp a fuse if you can't get the correct one. I have used 125 V fuses in replacement for 250V fuses. Theoretically they handle less power - P = V x A but seem to work. You did not under power the lights, the fuse couldn't handle the electrical load.

Radio Shack seems to be useless lately, good luck. You can try elecrical supply houses or auto parts stores. If you are unsuccessful there are mail order places that can get fuses - Newark Electronics is a huge place, Allied Electronics is another and I believe I've heard good things about Mouser as well.


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## Helen B (Nov 27, 2010)

The voltage rating of a fuse does not really come into play until the fuse blows. Then it will have the full open-circuit voltage across it. If the fuse is rated for a lower voltage than the open circuit voltage it may not be able to act as an insulator when it blows under a fault condition - therefore always go for a higher voltage than the circuit voltage rather than a lower one, if you can't get the correct voltage rating. There is no reason for 250 V fuses not to be used in 110 V circuits.

The fuse controls the current going through it, not the power in terms of rated amps x rated volts (ie the voltage rating of the fuse does not come into play, only the circuit voltage when calculating power).

If a fuse has blown, there may be a good reason - ie a fault. Your strobe could have a fault...

Best,
Helen


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## fokker (Nov 27, 2010)

Vinny said:


> You are right in the thinking that 5A 250V = 5 Amps 250 Volts.
> 
> To confuse matters, there are slow blow fuses and fast blow fuses. There are letters (AGC, ABC, ...) on them that indicate what they are.
> 
> ...



The voltage rating of a fuse has no bearing on how much 'power' it can handle. Amps (current) and amps only are the only thing that will make a fuse blow, or not. The voltage is important though, and if you put a 125V fuse in a 250V circuit you risk the fuse shorting and offering no protection at all. However as someone already stated you are probably using 110V power anyway so it shouldn't matter - with voltage ratings you can go higher but not lower. 
There is quite possibly a reason why the fuse blew in the first place - try replacing it with another 5A fuse (by the way the guy who told you that 5A 250V fuses are 'old' doesn't have a clue what he's talking about). If it blows again with the 5A fuse then something is wrong and do not try replacing the fuse with a higher current rated one.

/electrical engineer


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## Vinny (Nov 27, 2010)

When a fuse blows the voltage stops on the cord side of the fuse, it no longer has the ability to transfer electric. The lower voltage rating will only let it blow quicker due to less power handling capability. Years ago some manufacturers would fuse both the hot side and neutral side of the AC cord which would make for a dangerous situation if the neutral side opened first and I believe this is what you're referring to.

After writing my response before I realize that we are probably talking about 120 Volt light so 125 volt fuse will work OK as long as it has the correct amperage rating AND there isn't a problem with the lights.

Just a FYI, a fuse is made up of a temperature sensitive wire the opens up if the current exceeds its maximum. There are quick blow fuses and slow blow fuses.



Helen B said:


> The voltage rating of a fuse does not really come into play until the fuse blows. Then it will have the full open-circuit voltage across it. If the fuse is rated for a lower voltage than the open circuit voltage it may not be able to act as an insulator - therefore always go for a higher voltage than the circuit voltage rather than a lower one, if you can't get the correct voltage rating. There is no reason for 250 V fuses not to be used in 110 V circuits.
> 
> The fuse controls the current going through it, not the power.
> 
> ...


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## Helen B (Nov 27, 2010)

Vinny said:


> When a fuse blows the voltage stops on the cord side of the fuse, it no longer has the ability to transfer electric. The lower voltage rating will only let it blow quicker due to less power handling capability.



Sorry Vinny, but that is simply wrong. If the voltage rating is too low, the fuse may still conduct - that is what the rating means. The voltage does not "stop" on one side of the fuse.

Best,
Helen


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## Vinny (Nov 27, 2010)

*I stand corrected! *

I read up on a fuses properties and see that it is not a good idea to use a lower voltage rated fuse. I guess living in the US and dealing with 120 Volts I never came upon a problem situation ... and I won't going forward.


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## SrBiscuit (Nov 27, 2010)

Thanks so much for your responses all. I took josh's advice and went over to my local shack. They had the 5amp 125volt fuses and it absolutely did the trick. Now i have extras for next time.

So it sounds like with the 3amp, the strobe was trying to pull more amperage than the fuse could handle, and therefore blew the fuse. Is that accurate?

Thanks again everyone. Its great to know it wasnt a faulty head.:thumbup:


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## jfreaksho (Nov 28, 2010)

SrBiscuit said:


> *snip*
> 
> So it sounds like with the 3amp, the strobe was trying to pull more amperage than the fuse could handle, and therefore blew the fuse. Is that accurate?
> *snip*



This is correct.  What you can also do is look on your strobes to see what they draw.  They should be UL-listed, and have the power information printed on them somewhere.  If you have 5 of them and they are rated for .75A, or 750mA, then your total rating will be 4A, technically.

If you keep having problems, then at this point you can look into finding out what else is on that fuse- fridge, microwave, computer, tv, etc...- that will also be drawing current.  Think about what you can move to another circuit on a different fuse, giving your more of a buffer.

Sometimes when things power up, they draw more current than they are actually rated to.  There is a brief spike which can cause lights to dim or fuses to blow.  The less you have plugged into the circuit, the better off you'll be in this scenario.
J.


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## Helen B (Nov 28, 2010)

jfreaksho said:


> This is correct.  What you can also do is look on your strobes to see what they draw.  They should be UL-listed, and have the power information printed on them somewhere.  If you have 5 of them and they are rated for .75A, or 750mA, then your total rating will be 4A, technically.
> 
> If you keep having problems, then at this point you can look into finding out what else is on that fuse- fridge, microwave, computer, tv, etc...- that will also be drawing current.  Think about what you can move to another circuit on a different fuse, giving your more of a buffer.
> ...



Isn't the OP referring to the fuse in the strobe itself, rather than the fuse in the main board? (5 A is quite low for a mains strobe. For example my little Dyna-Lite UNI400JRs (400 Ws) take 8 A fuses and each of my larger Speedotrons has to be on its own separate circuit because of the current they draw when charging.)

Best,
Helen


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## SrBiscuit (Nov 28, 2010)

indeed....it was the fuse in the strobe itself, not on the house board.

thanks again guys and gals!


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## c.cloudwalker (Nov 28, 2010)

Helen B said:


> ...my larger Speedotrons has to be on its own separate circuit because of the current they draw when charging.)



WOW!  I take it your studio was not wired to be a studio... but I'm still surprised because my very first studio was in my 40's townhouse without any special wiring and I never had a problem.


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