High current fuses and circuit breakers

[mango]

I am wiring up the 12 volt electrics in a boat for a friend and was thinking of using a suitably rated 'mega fuse' in the inverter supply. ASAP Supplies sell these and seem to be one of the cheaper sources.

 

I would prefer to use a resettable circuit breaker on grounds of convenience. Can anyone suggest a suitable 12 volt circuit breaker? 150 or 200 amps rating would be needed.

[smileypete]

Blue Seas do a range of decent circuit breakers, cost a lot more than a megafuse or three though.

 

I wouldn't rely soley on the cheap ~£10 car circuit breakers alone without testing it and having at least some backup protection, in case the breaker gets welded on a short circuit. Ideally test the breaker trips after installing too.

 

cheers, Pete.

~smpt~

Edited May 27, 2013 by smileypete

[mango]

Blue Seas do a range of decent circuit breakers, cost a lot more than a megafuse or three though.

 

I wouldn't rely soley on the cheap ~£10 car circuit breakers alone without testing it and having at least some backup protection, in case the breaker gets welded on a short circuit. Ideally test the breaker trips after installing too.

 

cheers, Pete.

~smpt~

Thanks Pete. I've seen a few welded contacts when I was younger and used to sort out electrical problems.. I believe the inverter contains a fuse but was going to check if I went for a circuit breaker option.

 

Perhaps the best answer is to go for the mega fuse and ask the owner to be careful about what gets plugged in, or he can pay for an expensive breaker.

 

 

Do you know if it is still normal practice to have no fuse in the output from an alternator? That was common practice in the days when boats had a single services battery, but I hate to think what could happen if a battery bank discharged through a faulty alternator. I'm aware that a fuse will affect the maximum charge rate and that open circuiting an alternator is likely to kill it.

[smileypete]

Thanks Pete. I've seen a few welded contacts when I was younger and used to sort out electrical problems.. I believe the inverter contains a fuse but was going to check if I went for a circuit breaker option.

 

Perhaps the best answer is to go for the mega fuse and ask the owner to be careful about what gets plugged in, or he can pay for an expensive breaker.

 

 

Do you know if it is still normal practice to have no fuse in the output from an alternator? That was common practice in the days when boats had a single services battery, but I hate to think what could happen if a battery bank discharged through a faulty alternator. I'm aware that a fuse will affect the maximum charge rate and that open circuiting an alternator is likely to kill it.

 

In this case I'd rather for the fuse the inverter manufacturer recommends and supply a couple of spares too if poss. The fuse is mainly to protect the inverter cabling not the inverter, and should be put in the positive cable near the batt.

 

As for the alt and starter, if the cabling is well separated and properly protected and properly crimped up and heatshrinked and the terminal covered with a plastic boot, then a shorted cable should be quite unlikely. Having a sustained batt short through an alt would be extremely unlikely I'd expect, so any fuse would only be for short circuit protection due to cable damage or errant spanners, in which case a very high value would be OK.

 

cheers, Pete.

~smpt~

[mango]

I appreciate the need for sound connections, good insulation, protection from chafing, etc. but it's well worth the reminder. Plastic boots have been added to the shopping list.

 

In the 80s a friend had one of the Lucas ACR series alternator short, damaging the cable and wrecking a battery - hence my concern about an alternator connected to a bank of batteries. Knowing how low resistance shorted diodes are, I hope that modern alternators are designed so that something acts as a fuse in the event of a fault.

[smileypete]

Maybe fit a very generously sized megafuse then, dedicated to the alt. All the more reason to fit terminal boots/covers too, or a spanner ding on the B+ terminal with the engine running could blow the fuse and then the alt as well. Polevolt are quite a good source of 12V leccy bits including terminal boots:

 

http://www.polevolt.co.uk/acatalog/Battery_Terminal_Covers.html

 

Where several cables are going onto a terminal it might be worth considering using a small placcy box as a cover with an additional nylon dome nut and washers to hold it on:

 

http://www.ebay.co.uk/itm/PLASTIC-BOX-ENCLOSURE-CASE-HOBBY-ELECTRONIC-PROJECT-ABS-E43-/130739752372

http://www.ebay.co.uk/itm/M3-M4-M5-M6-M8-M10-NYLON-DOME-NUTS-Plastic-Packs-of-10-/400290238846

 

cheers, Pete.

~smpt~

Edited May 28, 2013 by smileypete

[by'eck]

I am wiring up the 12 volt electrics in a boat for a friend and was thinking of using a suitably rated 'mega fuse' in the inverter supply. ASAP Supplies sell these and seem to be one of the cheaper sources.

 

I would prefer to use a resettable circuit breaker on grounds of convenience. Can anyone suggest a suitable 12 volt circuit breaker? 150 or 200 amps rating would be needed.

 

A high current circuit breaker of any quality will be a high price to pay for the convenience. Can I suggest a good quality regular fuse/holder of inverter manufacturer recommended rating with a spare fuse in the unlikely event it blows.

 

TBH I don't think a circuit breaker is the correct solution in this case anyway. If the breaker drops out it will be for reasons that may have severe consequences requiring immediate investigation of the wiring or inverter itself, not just a matter of resetting.

[mango]

Thanks for all the useful links, Pete. I wish I'd known about the PoleVolt site at the start of the project. I'll do my best to make things spanner-proof.

 

The suggestion of a circuit breaker came from the boat owner, by'eck. I'm convinced it is a non-starter and plan to use 'mega fuses'. Thanks.

 

 

Incidentally, I have been presented with a 5 kW MSW inverter to wire up, mainly to run a small microwave oven. From previous experience microwaves hum a bit and the output is decreased on MSW, and that's what happened when we tested this one. The plan is to replace it with a sine wave one at a later stage.

[by'eck]

Yes my last boat ran the microwave rather poorly on a MSW inverter. The other side of the Atlantic it ran like on steroids with the 60 Hz shore mains supply though, although the timer was strangely slow.

[mango]

Off-topic, but I prefer to use a small MSW inverter to charge odds and ends when the engine is not running, even in boats fitted with good quality SW inverters. The latter can take quite a lot of power off-load.