Re-wiring 8D batteries

[Cold Shot]

Good morning fellas,

I’m ordering parts on Amazon now to rewire from new battery charger to two 8D batteries. It’s a 12v system with two Diesel engines. The main wire from charger to batteries is 4 AWG. I want to add a bussbar near the batteries and remove the wing nut terminals.. The system runs through two large Perko switches which I’ll keep. The new batteries aren’t charging well. The drawing below is a rough sketch of how I think it’s set up. I need suggestions on what to buy. Thanks for any suggestions in advance. I’m doing the work this weekend.

So far I have
15’ of new 4 AWG wire (red and black)
Lugs
Heat shrink

 

[KnotYet]

A crimping device of one kind or another will be necessary.
Also recommended is copper-based antisieze paste that keeps moisture out of the
wire to lug connection.
It's good to have a cable cutter big enough to handle the cable size you're using, too.

 

[Cold Shot]

Notes. I added those to my Amazon list. What about a busbar. Any specifics on busbars.

 

[KnotYet]

Blue Sea, available at West Marine and online has several types of buss bars and
remote terminals to choose from.

 

[bayview]

Short answer, Since you have twins I would wire the batts separately so that each engine is fully independent. You can have a combiner switch for emergencies or just use a jumper cable.

 

[kchace]

Short answer, Since you have twins I would wire the batts separately so that each engine is fully independent. You can have a combiner switch for emergencies or just use a jumper cable.

I agree with the above. I would also like to mention that your battery charger should not go through the battery switch (which appears to be how you have it drawn), it should go directly to the batteries. You can "access" the batteries at the switch by attaching the battery charger to the same lug that connects directly to the batteries.


Also, appropriate fuses are a must. And get as many non-engine start cables off the batteries as possible and fuse them.


Ken

 

[Cold Shot]

I’ve had issues with the new and older charger not charging two of the three batteries. I have a large platinum car battery for the old generator. I found the charging issue. From the charger the three red leads (6 AWG) go through a 60 amp fuse. Two of the three are fried (23 years old). I found them at Grainger. After the fuses the leads go to the Perko switch and is mounted with the leads going to the batteries (2AWG). The black lead go to the buss bar. The Perko switches stay on All. This was wired this way from the factory. What advantage would I have to bypass the Perko switches?

 

[Cold Shot]

I forgot to ask, what battery terminals would you suggest. Price isn’t a concern. Looking for reliability seeing as the boat stays in the slip. Amazon has lots of different kinds.

 

[C lectric]

One advantage is No one can turn the switches to OFF resulting in defeating the battery charger when you are counting on it to recharge the batteries overnight when at the dock. Fuse the charger outputs as close to the batteries as possible, officially 7 inches but as close as practical. If you run the charger outputs to the buss bars you are talking about then just before the busses. The batteries are the real danger in case of a short circuit and provide thousands of amps in case of a dead short.

THe charger should have its own fuses or circuit breaker in its own case.



I will also strongly recommend that you look up and buy a copy of
Nigel Calders book Boatowners Mechanical and Electrical Manual.
It explains a huge amount about batteries, connections and how to wire these systems. Not everything but a lot.

 

[Comodave]

It appears that the Perko switch is only used as an on/off switch since one of the terminals does not have any cables going to it. I would recommend on having the on/off function so you can easily turn the power off if you need to.

There is a thing called stacking. This is where you should put the cables carrying the largest load on the terminals first and then the next largest load and so on. On the back of the battery switch it looks like the small cables are on the terminal first so they should be stacked properly.

 

[Cold Shot]

Thanks Dave what battery terminals would you suggest? Amazon has lots of different marine grade terminals.

 

[AlanT]

A crimping device of one kind or another will be necessary.
Also recommended is copper-based antisieze paste that keeps moisture out of the
wire to lug connection.
It's good to have a cable cutter big enough to handle the cable size you're using, too.

If you don't want to buy the crimping device you can (most likely) use the crimping tools at West Marine. They are free to use in store (but likely only for wire purchased in store).

 

[AlanT]

Thanks Dave what battery terminals would you suggest? Amazon has lots of different marine grade terminals.

According to my surveyor wing nut connections are not 'approved' I do not recall if this was ABYC or not but you should avoid wing nuts and instead use nylock nuts get many spares as those should not be reused and you are going to be fiddling with this for a while

 

[C lectric]

Wing nuts are NOT a good way to secure the wires. I don't use Nylock nuts though. I have a supply of 5/16 and 3/8 silicon bronze nuts AND flat washers which is what I use on the cable securing bolts. I've never had one loosen on its own. I'll also add that the plated steel nuts are fine also.

I have been changing over a period of time to brass terminals for better conductivity. Again personal choice as the lead terminals work fine.

As for the style of battery terminal they all work. I do NOT use the long bolt, military type terminals. I want only the battery lead attached that then goes to a buss bar which is where all the other circuits are fed from.

I now use MRBF type fuses along with their holder for fusing at the battery itself. I don't have space for the standard fuse holders, like ANL, which although small still eat a lot of room. These are a BUSSMAN fuses but sold easily by Blue Seas.

 

[Comodave]

Absolutely no wing nuts. I use S/S nylock nuts without any problems. Do not put any washers between the terminal and the wires, only on top of the wires. Washers do not conduct well. I also use the MBRF fuses from Blue Seas.

 

[Cold Shot]

As for the style of battery terminal they all work. I do NOT use the long bolt, military type terminals. I want only the battery lead attached that then goes to a buss bar which is where all the other circuits are fed

So all the small black leads should go back to that buss bar and then 2AWG from battery to BUSS Bar?

 

[Scottwb96]

If you want to make your life simple, BUY these 2 tools. The wire cutter, was demo'ed to me at Fisheries Supply and I literally dropped my jaw! The guy cut through the thickest wire they had using 2 fingers!!!

https://www.amazon.com/Allstar-Inno...wer+cutter,+anvil&qid=1585676561&s=hpc&sr=8-2

For crimping, this tool works great for various sizes of lugs. Make sure you get a heat gun and shrink wrap as well...

https://www.amazon.com/gp/product/B017S9EINA/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[C lectric]

So all the small black leads should go back to that buss bar and then 2AWG from battery to BUSS Bar?

Yes, only ONE lead from the battery to the buss bar. All other connections then from the buss bar to the loads. Fuse each other load POS as needed close to that buss bar.

I'll add that both the POS and the NEG sides should be treated the same except the fusing.

WASHERS I wasn't clear but agreed , on top only of the wire lug, not between the lug and the battery terminal. Same for the buss bar, washer only on top of the stack whether only one lug or several.

As for the individual load wires connecting to the actual battery terminals it is difficult to get all of the lugnuts tight and if you ever need to disconnect some of them it is a recipe for problems with controlling them and possibly a short circuit.

On the buss bars you may end up stacking some but not a big pile of them. The more you stack the more trouble you CAN eventually have with servicing any of them and it also leads to too high a Vdrop especially where high loads like an inverter are concerned.
A buss bar can be twinned as needed to allow for more connections.


I see some of the wires are RED indicating POS and then the others are BLACK indicating NEG. That's good. I will point out that YELLOW is strongly suggested for DC negatives now. DO not discard all the black wires but just be sure to mark them, YELLOW tape.

Improve the marking to reduce any chance of confusion. Best is the heat shrink tubing in the correct size AND the correct colour. However if not then at least get and use RED electrical tape on the POS conductors, not black. Use YELLOW tape on DC negatives.

As you go then you will understand the need for the YELLOW. On boats with both AC & DC wiring there has been confusion between the black AC hot and the DC negative which can be very dangerous.

To reduce that potential they have started using YELLOW for the DC negatives. Thus the use of at least YELLOW heatshrink tubing or YELLOW tape at the wire end or lugs even on black wire to mark the DC neg..

 

[Comodave]

ABYC says no more than 4 conductors on 1 screw or stud. But I try to stay with no more than 3 because it just get to be a mess with that many connections in a small area. If I need to make more connections then I will put in a bus bar with more screws or studs on it.

 

[FF]

https://www.finditparts.com/product...MIydbyoInH6AIVFGKGCh0HaAALEAQYASABEgKQwvD_BwE

The "military style" work great and many parts places like NAPA carry them.

Its my belief that heavy loads like starting or inverters need a straight shot from the batts to avoid corrosion and loss of power .The military style can easily handle 2 serious wires.

AS connections need to be cleaned every so often , the fewer the better chance of the cleaning happening.

 

[Robertmark]

I always crimp and solder battery cables. I use a torch

 

[Comodave]

I don’t solder them as it can create a hard spot where the solder ends. With a proper crimp it should be fine.

 

[Cold Shot]

I just rewired the larger cables on the DC side on my boat including anything between 2/0 and 6awg. The wire I didn’t replace got corrosion cut out and recrimped with tinned copper connections. I installed a new battery charger. I installed Blue Sea 60amp MRBF terminal fuses near the two 8d batteries. After the first time trying to crank the engines it fried both fuses. I have a fuse bank with three of them but one connects through an extra battery and doesn’t start anything. I have 8d batteries on Cat 3126 engines. What amp fuses should I go up to?

 

[Xsbank]

A proper crimper compresses the cable strands into a virtually solid mass and soldering is a waste of time. We used to solder automotive terminals but don’t bother unless it makes you feel good. That’s the only reason.

You still need to fuse or circuit break the cables. Even on a start circuit, the fuse should be spec’d to protect from inrush current but still protect the cable. Think about runaway starters or a short of some kind that ignites the wires and burns up your boat.

Dielectric grease, sparingly used, is a good thing to put on battery connections to protect from corrosion.

Use a good source of information, like Blue Sea’s charts to calculate the correct cable size. Just because it is factory doesn’t mean it’s adequate.

How old are the 8ds? They don’t look recent. I would include a 24 hour charge, a 24 hour disconnected rest then testing every cell with a hygrometer.

I second the assertion to buy Calder’s book, it’s well-written and will save you a lot of grief, money and wasted time.

 

[Greg S]

... I installed Blue Sea 60amp MRBF terminal fuses near the two 8d batteries. After the first time trying to crank the engines it fried both fuses. ... What amp fuses should I go up to?

To start an automotive diesel engine takes between 500 to 1000 amps.
I think I know why your 60 fuse blew.

 

[Comodave]

I just rewired the larger cables on the DC side on my boat including anything between 2/0 and 6awg. The wire I didn’t replace got corrosion cut out and recrimped with tinned copper connections. I installed a new battery charger. I installed Blue Sea 60amp MRBF terminal fuses near the two 8d batteries. After the first time trying to crank the engines it fried both fuses. I have a fuse bank with three of them but one connects through an extra battery and doesn’t start anything. I have 8d batteries on Cat 3126 engines. What amp fuses should I go up to?

The MBRF fuses only go up to 300 amps. I put them on a previous boat that had 318 gas engines and the 300 amp fuses held but I doubt that they would hold on a diesel of any size. Start circuits, per ABYC, are not required to have fuses. On the battery charger the feeds to the batteries should be fused near the charger. Blue Seas makes a 3 circuit MBRF holder that works great for a 3 bank charger. The fuse for a 60 amp charger should be a bit bigger than 60 amps because all of the charging current could go to 1 bank.

 

[Cold Shot]

Omg!

 

[Bacchus]

If you are looking for some worthwhile info on crimping & crimp tools our own CMS has some great info and sells tools.
Worth reviewing and bookmarking for future.

https://marinehowto.com/

 

[Xsbank]

I have 350 amp fuses on each battery bank.

Its not logical to not fuse every circuit. The theory behind no fuses on a start circuit is the huge inrush current to a diesel starter and not being willing to risk a no-start with a blown fuse. If you don’t fuse and you fry the cabling or worse, you will have nothing left to repair, might have a fire and you will be much farther behind your attempt to start..

 

[Xsbank]

Take a look at Blue Sea Circuit Wizard, its a free app.