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Inverter fuse - Printable Version

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Inverter fuse - rheavn - 02-13-2013

Here is an item for owners of coaches with inverters that should probably be in your spare box. If it blows you will have no 12V house power or inverter. They come in different amperages, but the one on my coach is a 300 amp. The amperage rating for the fuse is marked on it. I do not have one on my starting batteries, but some Newells do. Here is one source, but I'm sure they are available many places.

http://www.solar-electric.com/f-300t.html

RE: Inverter fuse - rheavn - 02-13-2013

Here is a couple of pixs of how & where it is mounted. I would have thought it would be on the main positive, not the main ground. Maybe one of our electrical gurus can enlighten me.

RE: Inverter fuse - RussWhite - 02-13-2013

Steve,

Newell could have done many things better electrically in my coach than they did, but this is not one of them. It makes no difference what-so-ever which polarity of a circuit is fused. When there is just one positive cable, and one negative cable for a particular circuit, all the current that goes through one goes through the other. Breaking the circuit ( what a fuse does ) at any point stops all current flow. Often on a vehicle where the structure of the vehicle is used as a current carrying conductor ( ground is what it is normally called ) there well be multiple positive cables leaving a power source, and maybe only one negative cable from the body of the vehicle to the negative of the battery. Especially in those cases you can achieve circuit protection with just a single fuse on the negative instead of multiple fuses on the positives. I imagine that is what Newell did in this case. On my coach they fused some circuits from the starting and chassis batteries, and did not fuse others. Mine are ALL fused now. Failure of the insulation on any big positive cable leaving a starting or chassis battery and coming in contact with ground is going to produce one huge fault and I do not want to deal with. Should I ever have insulation failure my fuses will clear with no fuss or muss.
There is one other consideration worth mentioning. The negative cables from our batteries are basically at the same potential ( voltage ) as the surrounding steel and aluminum of the body of the coach. The addition of the fuse may result in extending an exposed connection closer to the body of the coach. It is just much safe to be working on an open connection that is negative and will not cause a huge fault should your wrench slip and come in contact with the body of the coach. That is why you ALWAYS disconnect the negative first when working on any negative grounded battery system.
Just remember before installing that spare fuse you wisely suggest to carry, there is probably some underlying reason the original one is open. Make every effort to understand the cause of the original failure before installing another fuse. Russ

RE: Inverter fuse - bikestuff - 02-13-2013

Russ,

Thanks for sharing! I was not clear on one point....

If you have a fuse on the negative terminal of both strings of batteries, haven't you done all you can do? On my coach, both sets are fused and I don't believe that there are any fuses on the positive side.

What did you mean when you said that some circuits were fused and some were not? Were the fuses on the positive side?

Thanks,
bill

RE: Inverter fuse - rheavn - 02-13-2013

I knew my EE friend would help me understand the issue and thanks for the free education. I would like to fuse my starting batteries, but would they too use a 300 amp fuse since there are fewer batteries? If not what amperage should I get?

RE: Inverter fuse - RussWhite - 02-13-2013

(02-13-2013, 08:00 AM)bikestuff Wrote:  Russ,

Thanks for sharing! I was not clear on one point....

If you have a fuse on the negative terminal of both strings of batteries, haven't you done all you can do? On my coach, both sets are fused and I don't believe that there are any fuses on the positive side.

What did you mean when you said that some circuits were fused and some were not? Were the fuses on the positive side?

Thanks,
bill

Hi Bill,

Yes, that is exactly what I meant. On my coach some of the positive cables were fused, and some were not. Remember, as Steve always says, no two Newells are alike ( and that is not always a good thing ).
From your description of your coach, yes that is all that is necessary if the negative on both sets of batteries is fused, you are protected! Hope that clear that up. Russ

RE: Inverter fuse - RussWhite - 02-13-2013

(02-13-2013, 08:12 AM)rheavn Wrote:  I knew my EE friend would help me understand the issue and thanks for the free education. I would like to fuse my starting batteries, but would they too use a 300 amp fuse since there are fewer batteries? If not what amperage should I get?

Steve,

I will have to do some reserach before I could answer your "how big is big enough" question. I can tell you right now, 300 is not big enough. Sizing the fuse is determined by the capacity of the wires and the draw of the load. In the case of our units, the number and size of the batteries is not much of a factor. We have more batteries in the coach side of things so we can supply lower amounts of current to our loads for a long time. However, on the chassis batteries, their job is to supply lots of current to that huge starter for hopefully a very short time. I do not have the specs on that starter readily at hand. This is a tough application because you don't want that fuse to blow while trying to turn the starter, just if the cable faults. My wild guess would be a fuse in excess of 1000 amps would be required. Interesting question... Russ

RE: Inverter fuse - bikestuff - 02-13-2013

Mine is labelled "I.R. 100KA DC". Russ, does that sound like the right spec? My motor is 500HP Cat C12.

Updated with picture.

RE: Inverter fuse - RussWhite - 02-13-2013

(02-13-2013, 09:34 AM)bikestuff Wrote:  I am having trouble with my picture...but mine is labelled "I.R. 100KA DC". Russ, does that sound like the right spec? My motor is 500HP Cat C12.

Well 100KA is another way of saying 100,000 amps. That is a whole lot of current. I am sure that is well above what the starter could ever draw under any circumstances, but it also seems like more than would be drawn even with a cable fault. I would think the resistance of the fault and cables would limit the current to a value less than 100KA, so just off the top of my head, that sounds too high. Russ

RE: Inverter fuse - encantotom - 02-13-2013

the one on my 90 was this fuse. 600amp

Class T Fuses A3T600 (300VAC/160VDC)
FERRAZ SHAWMUT
Fuses

there are several different manufactures with the same fuse.

they are going for 40-50 bucks on ebay.

tom