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| Adding reverse polarity protection help |
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| bigjoncoop:
Ive got a couple of RC lithium battery chargers and would like to add reverse polarity protection. The chargers are ISDT Q6 Nano's. Now the more expensive Q6 plus's have fast blow fuses on the output of the Chargers. The ones I have are a slightly cheaper version and they are using PTC resettable fuses instead of fast blow fuses... but they do not seem to protect the output mosfets from reverse polarity since I have recently blown two of these Chargers up due to reverse polarity. On both of them one of the output mosfets blew up... So I'm wondering if replacing the PTC resettable fuses with normal fast blow fuses might do the trick? Or if there is a simple method on implementing reverse polarity protection on the output of the charger that will not interfere with the charger functions. ANY IDEA'S? THANKS |
| CatalinaWOW:
Not aware of any simple electronic fixes. In general there are no fuses that are fast enough to protect FETs. The usual approach to this is polarized connectors. Several, but not all of the connectors used in RC are polarized. Color coded wires and painted cues on non- polarized connectors can help, but Murphy always gets by these precautions. Two prior failures indicates that you are one who needs more robust protection There is one case where there is a simple fix. If your problem is at the input of the charger (clipping to a car battery for example) you can put a full wave bridge rectifier in the lines leading to the charger. It will prevent connect the charger jmproperly regardless of how you connect the input leads and will have little or no impact on charger operation. Be sure to select a bridge capable of handling the current you expect to draw |
| perdrix:
I don't know if it works for this circuit, but take a look at this: If connected the right way round the MOSFET is just fully on, if the wrong way, the gate is pulled -ve which shuts everything off. I used an IRFS7537TRLPBF FET. David |
| thm_w:
https://www.eevblog.com/forum/chat/replacing-fast-blow-fuse-with-ptc-resettable/ |
| nctnico:
Put a (fat) diode across the mosfets which conducts when the polarity is reversed. Make sure there is a fuse in the path to the batteries though. |
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