Proper fusing of various charging sources

[Tom.B]

Isn't any way to expose an alternator to an unloaded state wrong? If the fuse blows for ANY reason, not just electrical, you'll lose your alternator too.

[twistedtree]

Originally Posted by R_C

I really appreciate this discussion. The attached crude sketch shows what I am now planning. Anyone see any problems with this configuration? The wire to the DC breaker panel is probably 1/0 AWG because of its length and the 100A fuse at the battery has been in place for some time. I'll add the additional 100A fuse at the busbar. Note that the Iota and Xantrex chargers are never run at the same time so the 100A fuse at the battery is sufficient. Others may disagree, but I've been using the rule that FLA batteries should be charged at no more than 25% of their Ah capacity.

I just really looked at this drawing now. Conceptually it looks fine, but I think the wiring is under-sized across the board. If you have 1/0 going from the bus bar to the electronics, then I'd use at least that from the bus bar to the battery, preferably 2/0 or even 4/0. In general, it's wise to oversize main cables like that since it's typically way cheaper and easier to do it now than to try to fix it later. Also, it's well worth running the voltage drop calculations for the different runs in their worst case configurations. I suspect you'll find that all your #6 wires are two or more sizes too small.

I also still think that the main battery fuse should be 200A, not 100A. Even if you don't plan to run both chargers at the same time, doing so shouldn't "break" the boat. Additionally, the Iota and your solar at full charge could exceed 100A.

The battery to bus bar run is the backbone of your electrical system. If I were doing it, I'd make it as robust and upgradable as possible. If possible, I'd run 4/0 cable and use a min of 200A fuse, preferably 400A. Then, for example, if some day you wanted to replace one of the chargers with an inverter/charger, your bus bar can handle it and it's a simple upgrade.

Either way, it's food for thought.

[Tellie]

Wire protection is very important on all circuits. I'd even suggest if you are going to do it yourself pay a few bucks and have a qualified marine electrician take a look at your work when you are done to sign off on it. I often work at the marina linked below. It would be bad enough if you lose your own boat, but taking a few others with you...I'd hate to think of that legal mess.


WSVN-TV - Crews to remove torched yachts from marina

The cause has yet to be determined, but I'd be willing to take a Mitt Romney bet that it's electrical.

[R_C]

Originally Posted by twistedtree

I also still think that the main battery fuse should be 200A, not 100A. Even if you don't plan to run both chargers at the same time, doing so shouldn't "break" the boat. Additionally, the Iota and your solar at full charge could exceed 100A.

Thanks for catching that oversight. I just verified that the busbar itself is rated at 150A so I will increase the main battery fuse to that amperage and the size of the wire from battery to busbar. All of the 6AWG wires from the alternator and chargers to the busbar are less than six feet in length and show less than a 2% voltage drop. It's only two feet from battery to busbar so that's a simple upgrade.

[twistedtree]

Originally Posted by R_C

Thanks for catching that oversight. I just verified that the busbar itself is rated at 150A so I will increase the main battery fuse to that amperage and the size of the wire from battery to busbar. All of the 6AWG wires from the alternator and chargers to the busbar are less than six feet in length and show less than a 2% voltage drop. It's only two feet from battery to busbar so that's a simple upgrade.

The specifics of everyone's situation are different. Sounds like you are doing all the right things to be sure yours works correctly.

[OceanPlanet]

Originally Posted by CarlF

MainSail. Hmm. Learn something new everyday. Now I know why there are two fuses in the alternator lead. Always thought the one at the alternator end was the more important but your explanation makes perfect sense.

Carl

This is especially true on multihulls or other boats where there is a long run from the alternator to the pos. bus (increased chance of a short somewhere). Another good idea to use a multi-pole breaker on the alt. end of the cable, with the alt. field run through one of the linked breakers. This way, if the wire is shorted and the breaker tripped then the alt. field is cut also.

Not necessarily applicable to the O/P; but here is a pic of such a breaker config. for a 250A x 14V alternator on a 55ft cat (cable run was 2 x 2/0 x 22ft from the breaker to the pos. bus).

[Maine Sail]

Originally Posted by OceanPlanet

This is especially true on multihulls or other boats where there is a long run from the alternator to the pos. bus (increased chance of a short somewhere). Another good idea to use a multi-pole breaker on the alt. end of the cable, with the alt. field run through one of the linked breakers. This way, if the wire is shorted and the breaker tripped then the alt. field is cut also.

Not necessarily applicable to the O/P; but here is a pic of such a breaker config. for a 250A x 14V alternator on a 55ft cat (cable run was 2 x 2/0 x 22ft from the breaker to the pos. bus).

Ocean Planet,

You were going to send me a link to that breaker this summer but I totally forgot about it. Can you forward that on to me when you get a chance.

Sorry for the hijack...

[OceanPlanet]

Email sent...sorry that I forgot too!

Back to our scheduled programming....

[mikefossl]

When I bought our boat none of the charging sources were fused. Nothing mentioned in the survey and I really didn't understand the mess of wires behind the main battery switches. Last summer I decided that I needed to clean things up (precipitated by the failure of our battery bank). After documenting the current state in a diagram and reading up on proper wiring I realized that it was a disaster waiting to happen. I re-wired everything connected to the batteries and every wire leaving the battery compartment is properly fused. I can sleep much better now.

[Kettlewell]

Isn't any way to expose an alternator to an unloaded state wrong? If the fuse blows for ANY reason, not just electrical, you'll lose your alternator too.

It's far better to lose the alternator than to lose the boat! What other reason would a fuse blow other than electrical? I suppose you could physically break it, but that would be very odd.

[chala]

Originally Posted by FlyingCloud1937

.then a fault develops on one of the other wires and blows the 100 amp main fuse,

According to the above scenario, a fault developed which fused a 100 amp fuse. The alternator is may be disconnected from the battery but is still connected to the fault which will overload the alternator. Two things among others could happen, the field collapse or the alternator overheat and burn out.
R C if it was my trawler I would do the following:
Assess how much current is likely to flow in the “DC panel” feed. 100 amp is unlikely and having two 100 amp fuses in series produce no discrimination.
Your drawing shows 3x150A batteries connected in parallel and also you intend to remove the isolator between the start battery and the house batteries. What is wrong with this is if one battery go down it bring down the lot. Also the batteries cannot be isolated and will mutually self-discharge. Instead of removing the start – house isolator I will provide each battery with its own isolator and fuse, I will keep the alternator connected to the start battery. I will have a simple voltage monitoring of each battery and the possibility to solar charge individually each battery. Also 25% Ah capacity for a 150A battery is 37.5A.

[FlyingCloud1937]

Originally Posted by chala

According to the above scenario, a fault developed which fused a 100 amp fuse. The alternator is may be disconnected from the battery but is still connected to the fault which will overload the alternator. Two things among others could happen, the field collapse or the alternator overheat and burn out.
R C if it was my trawler I would do the following:
Assess how much current is likely to flow in the “DC panel” feed. 100 amp is unlikely and having two 100 amp fuses in series produce no discrimination.
Your drawing shows 3x150A batteries connected in parallel and also you intend to remove the isolator between the start battery and the house batteries. What is wrong with this is if one battery go down it bring down the lot. Also the batteries cannot be isolated and will mutually self-discharge. Instead of removing the start – house isolator I will provide each battery with its own isolator and fuse, I will keep the alternator connected to the start battery. I will have a simple voltage monitoring of each battery and the possibility to solar charge individually each battery. Also 25% Ah capacity for a 150A battery is 37.5A.

Chala,

hehe, draw yourself a picture of the bat and a busbar, and various circuits attached to the busbar, now create short circuits to various of the loads and see what happens in all circuits.

Now fuse each circuit properly and create shorts in various of the loads and see what happens to the other circuits.

Lloyd

[chala]

Originally Posted by FlyingCloud1937

hehe,

I was not questioning the use of over-current protecting devices but the correctness of the statement below.

Originally Posted by FlyingCloud1937

Now just imagine that the alternator is connected to the bus and the engine is running...then a fault develops on one of the other wires and blows the 100 amp main fuse, that event has just caused a loss of connection from the alternator to the battery, and that will then blow all the diodes in the alternator.

By the way I would have installed an over-current protecting device between the bus bar and the small wire feeding the fuse box. (change of gauge)

Originally Posted by FlyingCloud1937

Attached is a pic

[AnchorageGuy]

RC, In looking at your sketch, if this were me, I would not connect both chargers as you indicate. There is always the possibility that you might have both chargers on at the same time, not a good idea. You might disconnect the one you want for back up and if one fails, make a re-connection. Chuck

[mitiempo]

Or just wire the charger's AC input from 2 separate breakers and they can be switched on and off at will. They should each have their own breaker anyway.