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Old 18-04-2022, 06:25   #1
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Fuses blowing

Have just finished setting up my Lithium batteries with a 60 amp DCC charger fed from solar / shore power via AGM house bank. Batteries showing charge rate of max 58 amps but keeps blowing fuses. I started with 70 amp trip fuse then a 70 amp ANL then a 100amp ANL but all blow even though they are rated higher than the current that is flowing.
Anyone have any suggestions?
TwT
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Old 19-04-2022, 20:32   #2
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Re: Fuses blowing

have you put a clamp meter on it?.. on the input line and the output?

in order to put 60a output it may need ~80a input if the dc to dc is not an efficient one
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Old 19-04-2022, 20:51   #3
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Re: Fuses blowing

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Originally Posted by smac999 View Post
have you put a clamp meter on it?.. on the input line and the output?

in order to put 60a output it may need ~80a input if the dc to dc is not an efficient one
Yes I since realised that as the input volts are less than the required output charging volts the ingoing amps will need to be higher. Good idea re clamp meter - will borrow one
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Old 19-04-2022, 20:55   #4
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Re: Fuses blowing

Y'all need to get testers. What in the hell. Test your electrical stuff if you are messing with it. The numbers are actually important....
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Old 20-04-2022, 18:00   #5
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Re: Fuses blowing

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Originally Posted by Toys_with_time View Post
Have just finished setting up my Lithium batteries with a 60 amp DCC charger fed from solar / shore power via AGM house bank. Batteries showing charge rate of max 58 amps but keeps blowing fuses. I started with 70 amp trip fuse then a 70 amp ANL then a 100amp ANL but all blow even though they are rated higher than the current that is flowing.
Anyone have any suggestions?
TwT
There are a few possible explanations for a fuse blowing at currents below its rating. One is elevated environment temperatures: the hotter the environment, the lower the current the fuse blows. This elevated temperature can come from external sources (e.g. battery charger nearby) or from internal sources (bad connection at the fuse). Pulsed energy delivery, such as from alternators and some chargers, also leads to the fuse blowing at lower average current as for the fuse the average square of current matters (in a resistor, the square of current is proportional to the produced heat). Would it be possible to measure the fuse terminal temperatures?

That aside, a fuse is normally sized such that it protects the wire, and the device current is not taken into account. Ampacity charts (e.g. http://assets.bluesea.com/files/reso...ence/21731.pdf) might be useful.
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Old 20-04-2022, 18:29   #6
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Re: Fuses blowing

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There are a few possible explanations for a fuse blowing at currents below its rating. One is elevated environment temperatures: the hotter the environment, the lower the current the fuse blows. This elevated temperature can come from external sources (e.g. battery charger nearby) or from internal sources (bad connection at the fuse). Pulsed energy delivery, such as from alternators and some chargers, also leads to the fuse blowing at lower average current as for the fuse the average square of current matters (in a resistor, the square of current is proportional to the produced heat). Would it be possible to measure the fuse terminal temperatures?

That aside, a fuse is normally sized such that it protects the wire, and the device current is not taken into account. Ampacity charts (e.g. http://assets.bluesea.com/files/reso...ence/21731.pdf) might be useful.
Thanks for that. Using AWG 2 cable so should be fusing at around 125 amps and fuse is in engine room but engines weren't running. Batteries are now fully charged so will wait until they are partially discharged and will test the fuse temperature both with and without engines running.
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Old 20-04-2022, 18:45   #7
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Re: Fuses blowing

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Thanks for that. Using AWG 2 cable so should be fusing at around 125 amps and fuse is in engine room but engines weren't running. Batteries are now fully charged so will wait until they are partially discharged and will test the fuse temperature both with and without engines running.
If the fuse blows when the engines aren't running, I think I might prefer to look into that case first because it factors out the engine heat. To avoid blowing too much fuses during testing, would it make sense to reduce the output of the DCDC to 30 A or so and increase it until a temperature rise can be observed (or the fuse pops)? BTW for spotting the temperature rise, a thermal imaging camera can be really useful.
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