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My Wine Fridge Ate Its Fuse

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Critic
User Rank
Platinum
Penny in the Fuse Box
Critic   8/9/2012 5:36:21 PM
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Replacing a fuse with one having a higher current rating because the original one blew is like installing a penny under a (screw-in) fuse in an old house.  It gets the circuit back online, but does not necessarily provide the correct level of over-current protection.  Perhaps the power supply had a maximum current capability of 3 A or less.  Perhaps the power supply should have had higher current cpability, but was chosen to keep costs low!  I am assuming that someone actually thought about the electrical design, but this might be an incorrect assumption on my part. 

This story reminds me of experiences I had many years ago with a power supply engineer.  He designed and built a 28-VDC, 100-A power supply which fed several curcuits requiring different current levels.  One circuit only required about 1 A, so he used small-gauge (AWG 24) wire for the 1 A circuit.  I asked him if he was afraid the wire would melt and start a fire if there was a short, and he responded that there was a 1-A fuse in the circuit in case there was a short.  What he neglected to consider was that there was 24-gauge wire connecting the power supply to the fuse!  If there was a short between the supply and fuse, then there would have been a fire.  In this case, the wiring up to the over-current devices had to be capable of 100 A.

BudM
User Rank
Silver
what is the real current draw should be?
BudM   8/16/2012 11:20:57 AM
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So if the measured current of the broken unit is close to 3A and the unit is using 3A fuse. How do we know  what the GOOD load current should be since we do not have the spec of the load? We are assuming that the load is OK, may be it is failing. Looks like more research need to be done before assuming it is bad design.

loadster
User Rank
Gold
Re: what is the real current draw should be?
loadster   8/16/2012 3:39:18 PM
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I concur with the comment that its important to know the rated current of the supply output as well as its nice to score a "free" vino cooler. I've played around with lots of the peltier thermoelectic cooling (TEC) modules and most work at 12 V with 3 A to 8 A current depending on their surface area and correlated P-N junctions. So they typically require a fan pulling less than a quarter amp and a power supply with 40 to 90 W capacity. What's important is what the switches and wires and ancillary circuitry were built to for current rating and dielectric breakdown. Derating from 3 A fuse to 4 A probably can't hurt you. No one reading these blogs should take away that its okay to double (or more!) fuse rating on any consumer electronics. What may have been a penny fix could result in a serious insurance claim and if the fire inspector finds the wrong fuse, your claim is done. Another consideration is those TEC used in chip coolers, auto coolers and wine coolers are woefully inefficient and limited and when they fail (due to condensation, fan failing or other), they're done. A standard dorm refrigerator uses approx. 300 kwhr per year, keeping food at chilly 40 deg. F with a thermostat. An equivalent TEC cooler will pull double that annual cost, run 100% duty cycle and the best they can do is about 35 degrees below ambient.  Not too green, that. For a wine cooler, that's okay but not if you like your beer frosty.

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