Mastervolt Installation and running new wires aft

Bob&Alicia

New member
I have made the decision to replace the Guest 5/5/10 charger with a Mastervolt 12-25/3. We may stay anchored in one spot for a more than one day and will have the reefer going and if it’s a “work” day we will have a couple of laptops/phones that need 12V charging. I have a generator and would like for it to be able to bring the battery back to full charge in as short of a time period as possible. Most days we will use around 35-40 AMP hours.

The Guest 5/5/10 is mounted to the right of the Hot Water heater under the aft most dinette seat. The wires run aft. I assumed that they ran straight back to the lazarette. They actually go under the Port Hanging Locker and turn and go by the cabin bilge bump located under the cabin step. I can see that they then go under the Head enclosure and come out under the sink. The wires are run inside a nylon mesh conduit. The conduit then T’s under the sink into another mesh conduit running down the starboard side from the battery lazarette to the helm. The Guest charger wires turn aft and run down the conduit to the aft lazarette. At some point they must have run out of red/black, red/blue, and red wires and switched up colors. One actually is Black and connected to the positive battery post. I have one set of wires connected to the Start Battery and Two wires connected onto the same positive post of the two 12 volts run in parallel.
I thought it would be easy to “tie” my new 10 AWG wires to the existing 16 AWG wires and “pull” the wires through. With this many turns and connections I am afraid I will end up with both old and new all messed up. Per the Mastervolt instructions I think it is wise to increase the gauge to 10 and not use the original wires so I really feel I need to replace the wires. I am thinking about disconnecting the Guest wires at both ends and putting a heat shrink label and heat shrink the ends and just leaving them in place. That way if I ever want to use the guest as a “second” charger it is already installed. I don’t see a good reason to remove the wires and I am thinking I just leave them in place in a disconnected state. I will have to do some more figuring.

The “best” route I can figure for the new 10 AWG wires is to go straight aft following the water lines. The water lines go under the hanging locker and then under the gas fill intake. There is a Beckson plate at the cockpit step and you can just get your hand in there to pull wires from the hanging locker. They then run aft and come out a maybe 4” hole on the port side right by the two 12 volt batteries. There are also large battery cables that run this same route for an inverter mounted above the hot water heater on the wood base under the drawer. I hope that I can get six 10AWG wires through here. I would like to add one more set of wires and “pre-wire” for a solar charger. I would think that the charge controller only needs one positive and negative wire and I would use 10 AWG since I am buying a spool anyway. This would be a total of 8 wires running this route aft. In a perfect world all of his is inside a nylon conduit sleeve and I manage to pull it all through together and have some chafe protection the entire route. I don’t have the wire put may cut 8 small pieces to get a diameter idea and see if it will fit. If they will not fit I am not sure of another route to take. I am guessing it is maybe a 15’ length of wire to go from the Hot Water cabinet to the aft battery compartment and giving yourself some wire to work with on either end. Does that length seem reasonable?

Has anybody done this? Do you see any flaws with what I am proposing? I am open to other route options as well. The last think I want to do is be able to get ½ my wires through and not the rest.
 
Your distance to the battery is 30 feet for figuring the wire size. (15 feet each way--although I suspect that it may be a little more than 15 feet. I have the same charger, and used #10 duplex wire (black and red in vinyl sheath) x 3. You will be marginal for 25 amps, but should be OK. (To have 3% or less voltage drop you would have to go to #6 wire--overkill for charging).

Where I see an issue, and only you can evaluate this, is getting the wire from the access plate to the batteries. There are probably several "bulkheads" under the floor. Running a bore scope type of video camera, or even a small camera in the area from both sides, will show any obstructions you may run into. It may have already been cut out enough when the inverter power cables were run thru there.

You can pull one of the inverter power cables, pulling several 1/8" lines to pull the new wires, and to pull the inverter cable back thru this area. I probably would not go with extra wires for the solar input. You can use one of the pair of #10 you are running now.

Be sure and fuse these wires at both ends, with 25 amp fuse or breaker.

I have 3 group 31 AGM batteries--which I run two refer/freezers off of. I use a 30 amp battery charger, which has a different profile (Longer in bulk) of charging than the Mastervolt charger. However, if you are just using 30 to 40 amp hours a day, the Mastervolt 25/3 should do well enough.

With this upgrade to your charging system, I have to ask, what size wire do you have going to the console? Generally I find the factory wire is in-adequate for minimal voltage drop. Check the voltage at the console and battery, with all power draw on: lights, refrigerator, electronics, radio, stereo fans etc. Be sure that you don't have over 10% voltage drop--ideally 3% or less.

Good upgrade.
 
Bob,
Really great advice. Thanks! I went on Amazon/Google and search for Borescopes and Endoscopes. I was shocked at how cheap they are now. The last time I looked at one it was several hundred just for a basic one. I can think of several uses for it.

I would not have put a fuse at both ends so I appreciate that tip.

I have never checked the voltage drop of the main to the console. I looks to be maybe a 10 gauge. I will do a voltage test on it.

You can pull one of the inverter power cables, pulling several 1/8" lines to pull the new wires, and to pull the inverter cable back thru this area. I probably would not go with extra wires for the solar input. You can use one of the pair of #10 you are running now.

I didn't follow on the above. At first I thought you meant to use one of the old Guest wires #16 to run the solar panel (might still be able to). That's what I first thought. The more I lay this out on paper I think I have incorrectly calculated how to wire the batteries. Currently two positive leads from my Guest charger go onto one positive battery post of one of the two batteries in parallel instead of one charging lead to each battery. I did some reading on this site and it looks like that might be OK. BUT, I should treat the two batteries in parallel as ONE bank. The higher amperage Mastervolt should only run ONE charging lead to one of the batteries. The 3rd wire run is NOT needed because I only have two banks (3 batteries with two in parallel and one start). Am I getting this right or am I more confused?

I will run some lines of paracord and use those to pull wires and if I have to pull out the inverter cable.

Thanks again for the input....very helpful.
 
I have mine set up a little different than you do--One of the reasons is that I run a negative to each battery (3 batteries)--so I assumed that you needed 3 negatives. That is not true for your set up; you only need one negative, which goes to the batteries--and they are all connected at the negative pole.

I have two batteries which can be used as house--or can be used as one house, and one dedicated to freezer. I have a switch which will combine these two, or not. Thus I put separate wires to each battery, and I run 3 positive--you only need two--see belo

In your case--just run two red wires. One to the starting battery, and one to the combined two battery (parallel) house bank.

You can use the wire to the house bank as the conduit to the batteries for the solar charger output. The wires are an extension of the positive battery posts. It makes no difference if they are hooked to the battery charger (which is protected by a diode--as is the solar charger or the battery terminal), So you can use this one wire for both the battery charger and solar charger.

You could use the #16 wire, but that may be a little small.

The manual for the Mastervolt calls for a 9 AWG wire minimum. I do believe that the #10 is OK--but #8 is far better to get the most efficient use of the battery charger.

Yes, I always leave a "Chase" cored when pulling wires. I use solid braid 1/8" rather than para cord, because I like it a bit better, but the para-cord is OK.
 
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