some 12V re-wiring questions

[Han]

Hi Everyone,

I'm back again for more help/advice, this time regarding the re-wiring project on our 30 year old boat. The current wiring is a total mess. I'm planning to start from scratch and, since it's a full overhaul, I'd like to do it right.

We have:
- 3 Trojan 27TM deep cycle batteries (105Ah each)
- A Beta 28hp diesel engine with a 65amp alternator (internal regulator)
- A battery charger for charging from shore power (make and model escape me right now)
- old panels which I'm replacing
- a 1/2/both battery switch

I think that our alternator is currently a bit undersized for the battery bank and I'm considering removing one of the batteries (our electrical demands are very light, no refrigeration, manual windlass, oil cabin lamps, etc). In addition I'd like to keep one battery dedicated for cranking and the other(s) for house use. To do this I'm thinking of replacing our 1/2/both battery switch with a battery combiner and switch (probably 7610-SI-Series automatic charging relay and e-series switch from Blue Sea) or an echo-charger, although I know less about these, so I'm a bit leery of them. If anyone has any insights please let me know.

My other question has to do with wiring in a battery combiner (or echo-charger). In my understanding the charger (alternator) should be wired to the house side, which will need the most charge. The starter on the other hand is wired to the cranking battery side. In our system only a single positive lead runs from the battery switch to the engine where it is bolted onto the starter. I believe that our alternator is wired to this same bolt and charges the battery via the same cable, but this was done in the factory and I'm wary of messing around with it. Does anyone know about this kind of setup, or have any ideas how I can work it into my new system?

Thanks in advance, and please let me know if all of the above rambling is unclear.

Han.

[AnchorageGuy]

I would strongly suggest you get a copy of the 12 Volt Bible and Nigel Calders book and do some studying and research. Your needs are going to be extensive and although you might get some good advise here it is a bit much to get enough advise to put together an entire electrical system from a forum.

[Han]

Thanks for the replies. I'm glad to hear the Blue Sea system works so well. I have just a couple more questions, my apologies if they're thick-headed.

1. I understand that the charging should be run to the house batteries since these will typically be the most depleted, and this saves running a large current through the relay from the cranking battery to the house bank. In our boat however, the engine has only two wires, ground and positive. The positive provides a charge for starting and the alternator sends its charge down that same wire back to the battery. In this case it seems impossible to charge on the house bank side, and the charging will have to be on the cranking side. Is this a problem? and if so, is there any (fairly easy) solution?

3. If charging is done on the cranking side and the house bank gets deeply discharged will the relay allow the cranking battery to be drained into the house bank while the system is charging? For instance, if we drain the house bank low, and then run the engine for only a short while, will the cranking battery drain into the house bank and leave neither capable of starting the engine since there hasn't been enough running time to charge the system fully?

Thanks!

[Zach]

I second Chucks recommendation on those two books, and have nothing to add to Knottybuoyz thoughts on your questions.

However... the stuff I wished I knew before starting out working on my wiring adventures:

Solid copper does not belong on board... anywhere. Stranded tinned wire is best... but not totally immune to corrosion unless shrink terminals and dielectric grease rule the day. Do not... use wire nuts. No matter how well electrical tape. By the way... there is only one electrical tape... that is Scotch 88. Even as totally righteous as it is... it pales in comparison to shrink tubing.

If you can run a continuous length of wire... do it. The less connections the better. Hard nylon crimp connections don't belong on board... use shrinking crimp connections and terminals. West marine isn't the place to go... buy them buy the box at NAPA, or better yet an wholesale electronic house. Put shrink tubing over every connection... no matter where it is, soldered or crimped.

Klein tools makes excellent wire strippers and cutters. But double crimps are the best way to go. Even a bargain basement double crimp goes above and beyond the standard "Smash it down" crimpers. You will however... want two sets of stippers. One with the stripper in front of the pivot, another with it behind, as sometimes the position doesn't allow the use of one or another without serious effort. The side cutters you use for wiring/cable cutters... are only going to be used on copper, or you will hate yourself after they are dulled by steel.

When you cut the tail off a zip tie, put down those side cutters... use a razor blade. Lay it up against the square block, push it into the tail... and pull on the end. Pop. You've created a stress risor that slices the zip tie off flush... No more gashed hands working on stuff. To get zip ties off, don't try to cut them... grab them with a pair of needle nose and give them a twist. Pop... no sawing and praying you don't harm the insulation on the surrounding wires.

I suggest you read through Acoustics guide on crimp connections... the best I've seen.
All About Marine Wire Termination Photo Gallery by Maine Sailing at pbase.com

As far as the wire gauge goes, I suggest going one step larger than whatever is required to curtail voltage drop and extend the time it takes for corrosion to negatively effect the system. SAE and AWG wire sizes are different so be aware. Buy a spool twice as big as you think you'll need, and then double it... of good quality boat cable. Or make up your own of high quality, 600v oil resistant stuff... If you do this... make a wire comb so you can keep all your runs neat and orderly. A rats nest is easy to create... Put a load of zip ties on loosely. Straighten out the run, and as you go every 6-10 inches sinch one down. Don't be afraid to add a ton of temporary ones... grab some really cheap flimsy ones and cut them off as needed when you add more wire runs.

I like the ABYC's recommendation that the 12v ground be yellow, though not necessarily that the whole length need to be... yellow shrink tubing on the ends suffices in my opinion. (Keeps you from grabbing a 110v (black) thinking it is a harmless dc ground...)

On your 110v receptacles... do not unscrew the screws all the way out and use ring terminals... they are knurled to prevent the AC's vibrating from loosening them. I like spade terminals with the ends bent up to positively lock them in place.

You can solder VHF and coax connections... so save yourself some money and don't go wild with funky connections! 30 bucks vs a little time, a little solder.. and some shrink tubing.

Leave enough extra wire everywhere that you can replace the ends a few times. There is nothing like having to patch in a new piece of wire on to the old one 4 inches from the end... That and make the control panels and fuse blocks wires long enough to work on the back side... be able to unscrew the whole shooting match and turn it around backwards! Perfect place for a drip loop...

Bus bars are a beautiful thing... Ring terminals and a bolt into something non-conductive do the same thing on the cheap, but by golly a nice bus bar is a lovely thing to work with.

Zach

[David M]

Draw everything out on paper. This means all lengths of wire runs, gunge of wire, terminals, loads, sources...everything. Stick to ABYC recommendations.

I too recommend buying a few books on wiring non-commercial boats.

[Han]

Thanks for all the replies. Knottybuoyz, thanks especially for your clear explanations. I've got Nigel Calder's book to guide me (that's what got me thinking about ACRs in the first place) but I'm sure I'll have more questions as the project progresses.

Thanks again.

[SilentOption]

I completely rewired our 30 year old boat and I strongly suggest you do as David proposed and make a drawing.
It can be simple and symbols aren't too important as long as you are consistent and know what you meant. Using the right symbols though can help as you later compare your drawing to a reference diagram like those found in books. You can add to it as you go and you can make notations on the drawing to remind yourself what is hooked to what. The drawing will be invaluable for troubleshooting.
If you take a few days and read from the books suggested you will save time and money. Another money saver is knowing what gauge wire to use for the different applications. Using too large of wire where its not needed is like throwing money away.
Do you plan to use the proper wire colors for different systems? If you use red for every positive circuit and don't tag or otherwise identify the wires troubleshooting can get pretty confusing.

Just some thoughts.

[knottybuoyz]

Drawings are relatively easy with the right tools. I use MS Visio Professional but you can use other CAD programs. Even Paintshop can do the job if you're so inclined. Here's one I did a long time ago for our project. I can help with yours if you like.

[Han]

Thanks. Nice drawing. I have a couple of drafting programs for work (autocad and autodesk inventor) which, although not meant for electrical diagrams, can probably be coerced into making something passable.

I hadn't really thought about the colours for the wire runs. Labeling was definitely on my mind though, and maybe using the proper colour coding would be an added benefit. I'll do as you suggest and measure all the runs/figure out all the wire guages before I get going.

[cal40john]

KnottyBuoys, I don't think that your statement that the combiner only turns on when the first battery is fully charged is quite correct. The battery combiner connects the two batteries together when the voltage of the battery exceeds approx. 13 volts. This is not when the one battery is fully charged. While this will not discharge either battery, you could possibly end up never fully charge the starting battery if the house bank never gets close to charged up during the times you are charging.



For the Echo-Charger the OP is correct. It is not just a battery combiner, it has a maximum output of 15 amps to top up the starting battery, so you must connect the charging source to the house bank.

Xantrex Technology Inc. - Recreational Vehicles - echo~charge - Product Information

John

[cal40john]

You say it works as you described which is that the combiner doesn't turn on until the starting battery is fully charged, then you provide documentation that it can turn on before the battery is fully charged. I originally said about 13 v because I didn't want to get into the details, but here is the info from Blue Seas.

Relay Contact Position: Combine (30 sec.)13.6 Volts@12 Volt
27.2 Volts@24 VoltRelay Contact Position: Combine (2 min.)13.0 Volts@12 Volt
26.0 Volts@ 24 Volt

If the voltage is parked at just above 13 volts for 2 minutes, it's because the starting battery is drawing a lot of current and somehow had become relatively discharged After these 2 minutes the battery will not be fully charged which is when the battery combiner connects the batteries.

In most situations, especially motorboating, this is not an issue as you will run the engine enough that everything will get charged. Even if you don't run the engine all day, the starting battery will get charged most of the way most of the time, but to flatly state that the combiner only turns on after the starting battery is fully charged is incorrect.

Also I did not say that there was anything wrong with wiring the Blue Seas combiner to the starting battery. You said that it was incorrect to wire the charging source to the house bank without identifying the fact that you were only talking about the Blue Seas device. Since the OP had also mentioned the Echo-Charger, I pointed out that with that device it is correct to connect the charging device to the house bank, then the Echo-Charger feeds some current to the starting battery.

John

Originally Posted by knottybuoyz

My experience is with the Bluesea product and it works as I've described. I guess in the end it's important you read the instructions that come with your kit. I don't know how the Xantrex unit works but it's quite possible its the way you describe.



From the Bluesea site...

ACR's or Automatic Charging Relays are automatic switches that close when the voltage on one of the batteries rises to a level (normally 13.2V to 13.7V) indicating the battery is connected to a charge source and is partially or fully charged. The switch then closes and shares the charging current with the other battery until the voltage drops to some lower level (normally 12.4 to 13.1 depending on model) and the switch opens. This prevents discharging both batteries when there is not enough current to charge both batteries.

Battery Isolators and Automatic Charging Relays - Resources - Blue Sea Systems

and from the illustration I provided earlier you can clearly see the charging source (alternator) is connected to the starting battery.

[knottybuoyz]

Obviously I've given some misleadign advice and have removed my posts.