Guest 51 Posted July 20, 2022 Share Posted July 20, 2022 How fast is fast blow? Sufficiently slow to cope with the inrush of an 80A windlass? Or the 380A for 750ms on the starter motor, when in emergency house start situation? These are spendy, I would like to get it right. Quote Link to post Share on other sites
Ladyhawk 37 Posted July 20, 2022 Share Posted July 20, 2022 https://marinehowto.com/battery-banks-over-current-protection/ A good read on such things 1 Quote Link to post Share on other sites
CarpeDiem 358 Posted July 20, 2022 Share Posted July 20, 2022 9 hours ago, Guest said: How fast is fast blow? Sufficiently slow to cope with the inrush of an 80A windlass? Or the 380A for 750ms on the starter motor, when in emergency house start situation? These are spendy, I would like to get it right. As a side note I put a 600A clamp meter on my 30HP engine starter motor a while ago and the inrush exceeded 600A... A single 300A Class T fuse should be all you need. It should take 900A for 1sec, but check the spec sheet for the fuse you are buying. This will be more than enough to not nuisance blow, but will blow in the event of a boat destroying short circuit. If you are setting it up for an Emergency start situation, then personally I would not fuse that circuit unless you have a long run cable between batteries. By very definition it is emergency and you will be there with it when you are using it and your batteries are probably next to each other. Instead put a 300A fuse on your starter battery and a suitable fuse for your house/windlass loads. 1 Quote Link to post Share on other sites
marinheiro 347 Posted July 25, 2022 Share Posted July 25, 2022 On 20/07/2022 at 12:32 PM, Guest said: How fast is fast blow? Sufficiently slow to cope with the inrush of an 80A windlass? Or the 380A for 750ms on the starter motor, when in emergency house start situation? These are spendy, I would like to get it right. What exactly are you looking to protect? Fuses are to protect the cabling, a windlass should have a re-setable circuit breaker -if your windlass draws 80 amps then a 100 amp breaker would be fine. Fuses need to be matched to cable size and depending on type they have an allowance for surge currents. I have a 3 battery system, the house bank has a 300 Amp Class T with a 70mm2 cable connection and a 200amp class T for the 2 kW Inverter feed, which is also 70mm2 Second battery is the starter, it has a 250amp Blue Sea stud mounted fuse, as does the third battery which powers the windlass, electric halyard winch and hydraulic pump to raise the centreboard, which I guess is about 1.0 kW (and takes about 30 sec to raise the board) All works well, I carry spare fuses but have never needed to use them 1 Quote Link to post Share on other sites
Guest 51 Posted July 25, 2022 Author Share Posted July 25, 2022 The cable from dead short and potential fire. I have the regular ANL fuses at 125-150% 0f continuous loads, on current FLA's. I am replacing FLA's with LiFePO4, so will need T class as well that has an AIC rating of 20kA's. I couldn't find the time current/time relationship, hence the question. I went with 300A, I still have to deal with the 400A headroom of the 2x bms's so am going to bypass them them with an emergency start battery (fail) circuit. Rob covered it here: Thanks CD & LH. Quote Link to post Share on other sites
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