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thanhquy2207
Joined: 27 Mar 2018
Posts: 1
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 Posted: Mon Jun 25, 2018 6:47 pm Post subject: Can a low voltage situation cause a fuse to blow? |
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Hello all. First, let me say that have very little education in the electronics field, but I do know the basics. I recently got hired as a service tech for pressure washers and had encountered a unit that had a small engine (electric start 12v) with a blown fuse. A co-worker of mine has been doing this work for about 15 years. He is the know it all type. Very good with wiring and troubleshooting electrical problems with the bigger electrical units (120v - 460v), however he told me that the reason this machine I was working on blew a fuse because the battery was low(which it was dead when it came in). I explained to him that according to my understanding of ohms law, that doesn't make sense. If the voltage was low the amperage should have dropped too. Is this correct? He told me that he has seen when low voltage had caused a fuse to blow or breaker to trip (in high voltage machines). Is there any situation at all that this would be true? It is really making me curious. Thanks for any insight you can help provide.
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user9253
Joined: 28 Mar 2008
Posts: 1931
Location: Riley TWP Michigan
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| Posted: Tue Jun 26, 2018 4:31 am Post subject: Re: Can a low voltage situation cause a fuse to blow? |
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A fuse holder with weak springs can create a bad connection which will make heat. Heat can blow a fuse. Not saying this is the problem in your case, but is something to check in future troubleshooting.
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Eric M. Jones
Joined: 10 Jan 2006
Posts: 565
Location: Massachusetts
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| Posted: Tue Jun 26, 2018 5:02 am Post subject: Re: Can a low voltage situation cause a fuse to blow? |
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First of all, low voltage IN GENERAL does not cause a fuse to blow. Look at all the cars with dead batteries for an example. Fuses are never even investigated.
Two phenomena contribute to the notion: 1) Back EMF, which reduces the running current when the motor comes up to speed, and 2) Starter circuits for motors which draw large currents UNTIL the motor gets up to speed. I won't go into the details, but they are similar, and both have to do with motor starting circuits.
I might add a third (rare) one: electronic circuits that try to keep an output constant. Usually these circuits have enough smarts to not blow an input fuse.
For circuits that only power resistive loads, fuse-blowing at low voltage is never an issue.
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Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
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alec(at)alecmyers.com
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| Posted: Tue Jun 26, 2018 5:13 am Post subject: Can a low voltage situation cause a fuse to blow? |
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I have a radio that requires 7.5A breakers on a 28v supply, and 10A breakers on a 12V supply. If the voltage drops the supply current requirement rises.
On Jun 26, 2018, at 09:02, Eric M. Jones <emjones(at)charter.net> wrote:
First of all, low voltage IN GENERAL does not cause a fuse to blow. Look at all the cars with dead batteries for an example. Fuses are never even investigated.
Two phenomena contribute to the notion: 1) Back EMF, which reduces the running current when the motor comes up to speed, and 2) Starter circuits for motors which draw large currents UNTIL the motor gets up to speed. I won't go into the details, but they are similar, and both have to do with motor starting circuits.
I might add a third (rare) one: electronic circuits that try to keep an output constant. Usually these circuits have enough smarts to not blow an input fuse.
For circuits that only power resistive loads, fuse-blowing at low voltage is never an issue.
--------
Eric M. Jones
www.PerihelionDesign.com
113 Brentwood Drive
Southbridge, MA 01550
(508) 764-2072
emjones(at)charter.net
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=481213#481213
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