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From: (no name) (no email)
Date: Sat Aug 14 1999 - 20:50:39 EDT
In a message dated 8/7/99 4:22:19 PM Eastern Daylight Time,
writes:
<< I've no idea why folks hook batteries up without fuses or circuit
breakers.>>
Both fuses and circuit breakers in sizes of several hundred amps are
expensive. I was lucky to find a couple of 100 amp ganged three phase
breakers in a flea market for about ten bucks each. I hooked them up with
the three gangs in parallel for 300 amp capacity using one breaker for my
house 12 volt buss and the other for my Trace 2.5 KW inverter. A
store-bought 300 amp single circuit breaker with the same interrupting
capability costs several hundreds of dollars. Even a fuse (I just looked in
vain for one in Home Power magazine), if I recall correctly, in that range,
is around $50 not including the fuse holder. - Norm
<<< We had breakers on our old boat, Saga, which did a great job of cutting
things off when there was a short. (Like submerging the batteries in sea
water.)>>>
A breaker will not protect against submerging batteries in seawater since the
"short" is upstream of the breaker. - Norm
<<<While breakers are somewhat expensive, fuses are not. They are easy
to find and don't cause any drop in voltage etc... >>>
Large fuses ARE expensive, and if you make even a quick accidential short,
say with a screwdriver or wrench, ZAP, you just blew $50.
Moreover, they DO cause a voltage drop, they have to (as do breakers) because
they depend on heat to melt, and heat, even before it gets to melting
temperature, means loss across the fuse to generate that heat. Put a digital
meter across a fuse that has current going through it and see for yourself. -
Norm
<<<They should be attached directly the to the battery, because you want to
stop the case when the battery bank provides current to a short (most common
case) rather than when there's a short on the way to the batteries. >>>
I don't quite understand this part. Fuses or breakers at the battery would
only protect the big fat battery cables going to your distrubution point.
Remember, fuses and breakers are to protect wires from getting really hot and
causing damage. Big fuses at the battery would only protect the big battery
wires from heating up too much. Small wires would melt with that much
current. You must size the fuse for the wire. - Norm
<<<You can also put a fuse at the output of the charger, for the same reason.
Do both, the fuses are quite inexpensive.>>>
All battery chargers I have seen have either a fuse or a circuit breaker on
the output line. Small fuses are inexpensive and should be used at each
branch circuit and at many electrical devices to protect against fire in the
case of an overload. - Norm
<<<The real reason for fuses is that a large battery stack has a gigantic
amount of energy stored in it. With Saga's stack we could actually weld! You
really need to limit the damage such a source of energy can do, and a fuse is
a great inexpensive way to do it.>>>
Yes, batteries do have a large amount of available amperage so that when
dealing with batteries, the fuses must have a large interruption capacity or
the arc produced when the fuse or cb opens could be as bad as the hot wire.
Also keep in mind that fuses or breakers will not always prevent electrical
fires. There can easily be a hot spot that reaches ignition temperature
without exceeding the rating of the associated fuse or breaker. After all,
the cigarette lighter gets hot enough to ignite the cigarette without blowing
a fuse. - Norm
<<< Beau
Boatless in San Francisco>>>
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