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Old 28-07-2019, 15:56   #1
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Poke holes in my wiring plan

About to do some upgrades and looking to simplify our wiring arrangement some. Currently have 8 Trojan T-105's, 2 60 amp centaur chargers, 1000W inverter and 2 engine alternators (100A and 120A). No centerfielder so we can't run both alternators at the same time, one just sits on the engine as a spare. More importantly absolutely nothing is fused.

We're replacing our batteries with 5x Firefly batteries, and our battery chargers with an inverter charger. Everything is 12 volt. Looking to get some input - I've attached a schematic (rough, sorry), feel free to give me some input but be nice! Credit to MaineSail's posts for this design, hopefully I translated his ideas correctly. I'm familiar with DC wiring but never embarked on a project quite this complex.
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Old 28-07-2019, 16:34   #2
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Re: Poke holes in my wiring plan

By the way the lengths on the drawing are not indicative of the physical lengths, all components are within 3 feet of each other.
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Old 28-07-2019, 23:19   #3
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Re: Poke holes in my wiring plan

Eng batt neg must go to load side of shunt.

The 1,2, all switches are wired weird.

If both alts have a reg then run them both.
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Old 28-07-2019, 23:48   #4
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Re: Poke holes in my wiring plan

Don't run your five paralleled battery leads to bus bars. Use short jumpers from battery to battery and the two long(er) cables to your distribution point. If the batteries are all lined up side by side the jumpers can be very short - only a few inches each. This avoids all the extra mess and cost of a lot of heavy wire. Neatness counts.
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Old 29-07-2019, 00:06   #5
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Re: Poke holes in my wiring plan

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Originally Posted by smac999 View Post
Eng batt neg must go to load side of shunt.

The 1,2, all switches are wired weird.

If both alts have a reg then run them both.

Hi, they look ok to me, the option to select the power source from either battery bank, pretty much the way mine are wired.
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Old 29-07-2019, 05:23   #6
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Re: Poke holes in my wiring plan

Wire your battery carefully such that the cable lengths between +/-are the same, kind of mirrored. I've seen diagrams presented here and somewhere on line, I think it was the Merlin website, for precisely how to wire batteries in series and parallel. Perhaps someone has a link for you. I know, now look a marinehowto.com
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Old 29-07-2019, 07:02   #7
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Re: Poke holes in my wiring plan

The batteries are wired to a bus bar like that based on a link someone referenced on here saying that, especially in banks with an odd number of batteries, the middle battery could get less charge due to resistive losses in the connections.

Also the way the switches are wired came from Maine Sail's post here: https://forums.sailboatowners.com/in...usings.137615/ How should they be wired differently?

If the engine starter is already on the load side of the shunt, why also wire the batt negative there as well? Wouldn't that effectively bypass the shunt?
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Old 29-07-2019, 07:06   #8
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Re: Poke holes in my wiring plan

I suggest that you also check out the numerous other threads on DC wiring.
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Old 29-07-2019, 07:25   #9
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Re: Poke holes in my wiring plan

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I suggest that you also check out the numerous other threads on DC wiring.
I have in fact done a lot of that already, hence the semi finished design. I'm simply asking for some validation that I got it right!
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Old 29-07-2019, 07:30   #10
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Re: Poke holes in my wiring plan

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The batteries are wired to a bus bar like that based on a link someone referenced on here saying that, especially in banks with an odd number of batteries, the middle battery could get less charge due to resistive losses in the connections.
This would only be an issue if the connections were loose or not done properly. Odd number of batteries? So what? The battery on the end of the chain is the one that would have an issue if there were poor connections.

Use appropriate sized cables for the loads and properly crimped terminals - there will be no problem.
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Old 29-07-2019, 08:02   #11
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Re: Poke holes in my wiring plan

I'm struggling to find the article that I found earlier, but this is a similar one which illustrates the issue. https://www.impactbattery.com/blog/t...s-in-parallel/
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Old 29-07-2019, 08:13   #12
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Re: Poke holes in my wiring plan

Yep here's the original article that I found but it is pretty much identical to the other one. The reason I went with the terminal block instead of the last configuration they show as being "ideal" where the batteries are jumpered is because their example is 4 batteries, and I'll have 5, so i wasn't quite sure how that would translate to ensure even charging.

http://www.smartgauge.co.uk/batt_con.html
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Old 29-07-2019, 08:35   #13
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Re: Poke holes in my wiring plan

The switch wiring also seems wierd to me......and could be very confusing.

I have to assume that the switches are "1,2,all" switches, otherwise you can't start the engine with the house bank. Even if they are "1,2,all" switches the top switch must be in the "all" position to start the engine with the house bank.

Far better to replace the "1,2,all" switches with simple "on,off" switches. Left side of the switches go to each battery as you show, and the right side of both of the switches are paralleled to house DC, starter, and windless. That way you can run everything off of one bank or the other bank or parallel them.

Simple and less confusing.

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Old 29-07-2019, 09:08   #14
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Re: Poke holes in my wiring plan

Would say your switching system is over complex. No need to wire a start batt to anything but the starter and its charging source. If you ever need to use the house bank to start the engine use a set of jumper leads.

Unless you have a good reason for either/or switches simply having an on/off fire switch is more robust and simpler ditto connecting the bank up with short links rather than to a bus bar.
Why firefly? Lots of people seam to want to go the expensive high tech route on batteries which makes sense if you have large 120v loads and high daily draw down but with a 1Kw inverter what needs the current capability of a firefly batt? For anything under 200A/hr day at C7 or less FLA is still the most cost effective solution. (but make sure of proper 6v or 2v deep cycle cells, if it is 12v it is probably not deep cycle whatever the label says!)
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Old 29-07-2019, 09:37   #15
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Re: Poke holes in my wiring plan

I saw Maine Sail's recommendation of just using on/off switches, agree what I've laid out is more complex but the use of the 1/2/Both/Off switches is more of an attempt to re-use what I currently have (which is actually two seperate house banks through THREE 1/2/Both/Off switches, so going from 3 to 2 seems like an improvement to me!)

Why firefly batteries? Well I'm impressed by the number of cycles they claim, numerous accounts here on CF of people actually trying to kill them only to go revive them back to 100% original capacity. We're replacing the 1kw inverter with a 3kw inverter, what we have now is not enough. Firefly seemed like a good compromise between the cycle life of LFP, cost and durability.
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