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Old 05-29-2016, 11:28 PM   #1
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Undersized wiring from battery charger

Shortly after taking ownership of our boat, we noticed issues with the house batteries not staying charged. Initially appeared to be old dead batteries but after replacing batteries (which actually were not in too good of shape) we noticed the new batteries also could not stay charged. For reference we are connected to shore power and the batteries are maintained by a Xantrax Truecharge 40. After a thorough review of the charging system, it became apparent that the #12 AWG wiring from the charger to the battery wires was grossly undersized. The wires would get hot to the touch and the 30 amp fuse would blow whenever the charger tried to go to max charging output. See picture below:
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After two episodes of this, I moved the battery charger re-wire up to priority #1. I replaced the DC wiring with new #8 AWG, new lugs properly crimped and heat shrinked, and new 40 amp circuit breakers. See after picture in next post as I can't figure out how to put more than one picture per post.

Oh, and the pictures are sideways because I can't figure out that part of posting a pic either.

And I have no idea why they had three separate negative wires coming from the common lug of the charger all to the same common lug of the batter bank negative terminals.
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Old 05-29-2016, 11:32 PM   #2
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Below is the picture of the re-word charger with correct sized wires for the amp load of the charger.
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Again, the picture is sideways.

I am happy to report that the new wiring is managing the full charging capability of the charger without tripping the breaker or heating up the wires like the old configuration did.
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Old 05-30-2016, 12:18 AM   #3
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I hate to say it but other that the larger wires and new terminals that still looks like a bit of a mess to me. I don't understand the need for the terminal lugs? They appear to be just a needless point of potential failure.

I'd just run wires straight to the batteries or perhaps the battery side of the battery switches. Depending on we're things are.

As to the sideways pictures, I've found if I take the picture with my phone on its side the picture posts vertically. I have no idea way. But it works for me.
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Old 05-30-2016, 07:48 AM   #4
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Your install looks good to me. Hope it solved the problems. You can never have wire that is too big. 😎👍
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Old 05-30-2016, 08:52 AM   #5
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Where did the fuses' go or did you figure out what they were there for? I believe the manufacturer and electrical code recommends either fuses or circuit breakers, be installed, for each positive lead, usually within 7" of the battery.
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Old 05-30-2016, 08:52 AM   #6
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Quote:
Originally Posted by Capt.Bill11 View Post
I hate to say it but other that the larger wires and new terminals that still looks like a bit of a mess to me. I don't understand the need for the terminal lugs? They appear to be just a needless point of potential failure.
+1

Did you at least look under the electrical tape? I'm guessing there might be some corrosion there. Heat shrink but connectors would be a better choice.

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Old 05-30-2016, 09:32 AM   #7
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The things that look like lugs in the second picture are the 40 amp circuit breakers that replaced the previous 30 amp fuses. These circuit breakers Meet the code requirement for overload protection. They are marine rated and water resistant. From the circuit breaker, the wire goes straight to the battery banks. I had to come home to get the tie wraps to tidy up the installation a bit.

The prior installation also had fuses on two of the three common negative terminal wires. This is not required by code here. I also replaced the three parallel redundant negative terminal wires with a single common negative terminal wire.

I did look under the electrical tape on the lug ends of the battery cable. No corrosion. I did not have shrink tube to fit that size wire and connector at the time of installation and the local supply store is closed till after the holiday. So tomorrow I should be able to get those shrink covered.

And yes, it has solved the overloading and over heating problem on the charger leg managing the house battery bank.
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Old 05-30-2016, 09:51 AM   #8
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Your picture shows a fusing principle that is often violated in boat wiring. Those new breakers (as well as the old fuses you replaced) only protect about 8" of wire- the wire from the breaker to the charger. The run from the breaker to the battery is not protected unless there are other fuses near the battery.


There are two sources of current in a battery charger installation: the charger and the battery it is connected to. The charger source can be ignored as it can only put out 40 amps, assuming that the wire is sized properly to carry that current. It is the battery which can supply a thousand amps where the fuse protection needs to be located, as Larry notes above.


And fusing the negative wire as on the original installation indicates a total lack of knowledge of boat wiring principles. I have seen a lot of fuses in the wrong place, but rarely fuses on the negative wire.


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Old 05-30-2016, 10:09 AM   #9
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David, you are correct. The breakers are to protect the charger wiring and are installed accordingly to the charger as the power source. There is a fusible link disconnect between the house battery bank and the safety switch that bank is connected to. This disconnect is a much higher amp rating, around 2000 amp I think but I need to verify that. There is no such disconnect on the generator battery or starboard engine battery as these batteries are dedicated to engine start only and do not operate any of the house DC circuits.

And I agree with your statement on fuses in the negative wiring. That was one I had never seen before either.
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Old 05-30-2016, 10:41 AM   #10
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What does the 40AMP charger rating mean? 40 Amps total of the three or is 40 amps available at any single outlet.
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Old 05-30-2016, 04:21 PM   #11
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What does the 40AMP charger rating mean? 40 Amps total of the three or is 40 amps available at any single outlet.
Those chargers can direct up to their 40 amps among all three or to any one output as required.

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Old 05-30-2016, 04:36 PM   #12
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David, you are correct. The breakers are to protect the charger wiring and are installed accordingly to the charger as the power source. There is a fusible link disconnect between the house battery bank and the safety switch that bank is connected to. This disconnect is a much higher amp rating, around 2000 amp I think but I need to verify that. There is no such disconnect on the generator battery or starboard engine battery as these batteries are dedicated to engine start only and do not operate any of the house DC circuits.

And I agree with your statement on fuses in the negative wiring. That was one I had never seen before either.
Those breakers may be marine rated but even if so they are the bottom of the barrel. Breakers per se aren't even needed in that circuit, fuses would be better and cheaper than good breakers and should never blow unless a genuine fault occurs. As David stated, any wiring connected to a battery (with the possible exception being the starter cable) should be fused as closely to the battery as possible to prevent a fire should a short develop anywhere along that wire. Those breakers do not in any way protect the charger, and the charger output will be protected within the charger in several ways, but the wire connected to the battery has the huge potential of the battery behind it at all times. Fusible links should only be used in rare and carefully engineered situations. Using your example, if you have a fusible link that blows at 2000amps, can the wiring connected to that handle the current in the interim?

Now that there are things like terminal fuses, adding fuses to battery wires is easier than ever.

https://www.bluesea.com/products/cat...0Fuse%20Blocks


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Old 05-30-2016, 05:27 PM   #13
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We have an older Xantrex TC 40 charger. The recommended fuse size is 50 amps per battery being charged.
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Old 05-30-2016, 05:37 PM   #14
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You start by saying the batteries will not stay charged and then determine that this is because the wires are too small. This makes no sense. If the batteries will not stay charged it is because one or more of them is defective or there's a constant load draining the batteries.
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Old 05-30-2016, 05:54 PM   #15
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I have 8 gauge wires from charger-converter to the wiring under the helm onto a terminal strip, about 7 feet long for 2 banks. Then from there it is 6 gauge wires to battery switch, the unswitched side. So even if battery switch is off the connection is live to the charger and alternators. However there are 80 amp fuses inline for each bank, so conceivably, a dead short will blow that fuse.

My charger wires are joined to the alternator output. My charger output turns off if the engine ignition turns on, some internal charger circuit monitors banks 1 and 2 only, but also turns off bank 3 if a main engine starts up.

Doing this way, the alternators can not be switched off at a battery switch, which protects their diodes from exploding.

Running longer to gen for third bank, is a 6 gauge wire.

As the gen has it's own onboard battery charger, I placed a relay to open circuit the charger-converter wire bank 3 only if it starts up. It never had such a thing, but I thought it might should have that.
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Old 05-30-2016, 07:31 PM   #16
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Quote:
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You start by saying the batteries will not stay charged and then determine that this is because the wires are too small. This makes no sense. If the batteries will not stay charged it is because one or more of them is defective or there's a constant load draining the batteries.
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