I was reading in the Xantrex manual that you must use a fuse and disconnet between the positive leg of the batteries and the inverter. I was thinking of using a Class T 400 amp fuse and a 400 amp rotary type switch. I was wondering though if I can use a 400 amp AC breaker instead. Some are going cheap on E.
Thanks for the help!
Pat ;)
Only if it's DC rated.
Ed
I would be very careful. You may void any warranty you might have with your inverter by not using the exact recommended set up.
Grant
I used a 225 amp breaker from a UPS that was being dismantled. The breaker actually breaks both the positive and neutral. The breaker almost looks like it was originally three phase as it has three connections with one connection connected across to one of the other lugs.
I figured if it worked on the DC side of a large UPS it should work for me. I have a 24 volt inverter which is why 225 amps.
It is common practice when using AC breakers for DC applications to connect two sets of the contacts in series which significantly increases the voltage breaking capacity of the breaker.
The bottom terminal of one set of contacts is connected to the top terminal of the second set of contacts to accomplish this. In much of the equipment that I manufactured I typically did this for the 600 volt DC battery source that fed the equipment.
I do not recall for sure, but I believe that all AC breakers are rated for at least 50 volts DC.
Richard
I certainly wouldn't challenge anything that Richard would offer as far as this situation is concerned because he has the experience and testing behind his recommendations....but (and isn't there always a 'but?) while the more learned among us might know well that it will work...how would the Underwriters for the Insurance Company feel about it should the be an 'incident' wherein there was an injury or even a total loss?
We all have Liability Coverage on our buses and probably most have coverage for a total loss. Should the Inspectors find something which would allow the Underwriters 'off the hook' and we didn't have the expertise to explain something which was installed 'not to code', therein lies the rub.
I don't wish to be a wet blanket on ideas...but the conservative side of me always keeps an eye on where I stand from a Liability standpoint inasmuch as I am 'the builder'.
FWIW.
NCbob
Everything I manufactured was either UL, ABYS or Lloyds listed. And if it is below 50 volts DC, UL is not even interested in how it is done. They feel there is no personal safety hazard at that level.
Richard
Richard, I'd be the last person in this world to challenge you or your knowledge. I don't know first hand of an AC breaker (by Brand name) which would do the job....perhaps you might.
Sometimes I play the 'Devil's Advocate' only to remind our friends that 'balls to the wall' or 'let it all hang out' won't do the job.
No offense meant or intended.
NCbob
In series, Richard? I would have thought that in parallel would be more effective by doubling the contact area.
Quote from: Nusa on September 08, 2007, 08:30:59 PM
In series, Richard? I would have thought that in parallel would be more effective by doubling the contact area.
Yes,
in series. Then you have two sets of contacts breaking the DC voltage at the same time, significantly increasing the voltage breaking capability of the contacts, whether in a breaker or a contactor or relay.
If I were doing it I would probably use a three phase breaker and series all three sets of contacts. There is absolutely no reason, in my opinion, to break both the positive and the negative leads.
Richard
While I couldn't tell you off hand where to find one, there are 400 amp, DC rated breakers available. They are used in telephone company power plants all over. A search for telco surplus might find something.
Len
DC rated breakers are available and they are very expensive. I have had to buy 800 amp units rated at 600 volts DC and they cost a small fortune.
I reiterate however, that for DC voltages below 50 volts, UL does not require a DC rating. The voltage is so low that it can not sustain an arc when the contacts open.
Richard
The only reason I switched both positive and negative is the breaker was wired up that way from the UPS. I guess I could have bypassed the breaker with the negative wire. I wonder if breaking both postive and negative at the same time is hard on the inverter?
While I have no opinion on AC circuit breakers....I can tell ya'll where to find 400 A DC circuit breakers. Electric vehicle builders use them.
www.EV-America.com is one source. Electro Automotive is another.
They are used as a sort of emergency shutdown devices. Often located within the drivers compartment (not the best of ideas), or remoted with a Bowden cable. The EV companies also have very large contactors for DC loads. Like big enough to handle bus starters. However, they are expensive.
Another idea is ANL fuses....not a recommendation...just something that isn't expensive and will protect DC circuits.
i'm in the process of converting a Nissan 200SX into an electric vehicle. Just bought some of the above components. For what they cost, I thought that they would be gold plated...they ain't.
Anyway, the EV folk sell large amp DC load components with 12V DC control voltage.
JR
I think one reason the manufacture wants a fuse and not a breaker is that if and when the fuze blows, they do NOT want the circuit reestablished quickly or easily. Particularily not an automatic-resetting breaker. Perhaps the requirement just comes from their legal department and has no real engineering reason. These things happen.
I would say that chances are 99 out of 100 that you will never blow that fuse and it is certainly much less expensive than a CB. When a 400 amp fuse blows, you will know it and so will all the neighbors.
Len
Another reason for manufacturers recommending fuses over circuit breakers may be the speed at which they open. A fuse is much faster.
Large DC Circuit breakers are expensive in comparison too.
JR
Pat,
The Xantrex setup that I've read requires a T-fuse.
Mostly the reasoning behind it is that the T-fuse is nearly fast enough to possibly save the electronics in the inverter. Breakers aren't.
Do it your way, but if it's a new inverter under warrantee, I would put the fuse called for in it. It might make your case for replacement a little more tenable.
Just my way...
Dallas
Wow, lots of speculation on here from folks who, apparently, have not even read the documentation for your inverter before telling you why you can't do certain things.
So that I don't make the same mistake, perhaps you can tell us the model and voltage of your inverter? After all, Xantrex makes the manuals for all their inverters available on-line.
FWIW, my own Xantrex inverter manual says nothing at all about preferring a fuse over a breaker. It does, however, stipulate that the maximum allowable fuse is 400A, whereas the maximum allowable breaker is 250A. While this may seem like a big difference, the fact is that the 250A breaker will provide better protection for your wiring, batteries, and inverter, and will only be a minor inconvenience if it ever trips, while the class-T fuse will likely be a real project to change.
Xantrex, BTW, will be happy to sell you their own branded 250A DC breaker for this purpose. If you can get by with 200A, Square-D's QO-series breakers carry DC ratings, and there is a two-pole model available in that size, available at almost any home center for a reasonable price, with a two-pole enclosure commonly available for around $15.
I have a 400A class-T (actually, two of them, since I have separate 24volt and 12volt feeds off my battery bank). I figure that if it ever blows, I have bigger problems than how hard it is to change the fuse. Also, the fuse holder takes up less room than a circuit breaker and enclosure. Lastly, my cables are four-ought, and getting cables that big into the panel and onto the lugs is a challenge. YMMV.
-Sean
http://OurOdyssey.BlogSpot.com