DC Wiring Diagram

[knitchie]

There have been several threads from people verifying their variation for wiring their boat; different components, different pictoral formats. Well, here is mine that I compiled from the documentation for each of the new components that I'm adding. After hours trying to comprehend everything, this is what I have come up with. My biggest concern is that I have done something really stupid, but wouldn't mind hearing better ways of configuring the circuit too.

A couple specific questions:
1) Do I need fuses between the isolator and each battery? If so, how large?
2) Should the ampmeter, which I want to use to monitor draw from the batteries, be moved ahead of the branch to the voltmeter and BATT on the ignition switch?
3) Should the Power line on the regulator go directly to a battery or to the Common post of the switch?

1293

Thanks,
Ken - Obsession
'78 C30 TRBS #0973
Lake Champlain, VT

[rigspelt]

Ken, can you post a larger image of the schematic?

[knitchie]

This is the first time I've attached images on this site, so I'm not quite sure how to control the image size. If you click on the gif image, you can copy or save it to view in whatever tools you have on your system and may be abel to adjust the size. But, later today I'll see whether saving it in a different format helps. Funny, we're usually complaining about images that are too big.

[High Hopes]

1) No, not if these leads are short – i.e. the isolator is located next to the batteries (which it should be). You may want to fuse the circuit from the alternator to the battery isolator with a 60 Amp fuse.
2) Yes, that way you will be measuring all the current and not just house current.
3) To the C post of the Ignition Switch.

I would drop the coil / tachometer fuse down to 7.5 Amp, and drop the 40 Amp to the ignition switch down to 25 amp.

The power circuit for the regulator should run to the Common post on the battery switch, and not go directly to the battery. This defeats one of the purposes of having a switch in the first place. You want almost nothing going to the batteries directly.

Also, you can add a diode in the regulator sense circuit to bump up your alternator output voltage to compensate for the isolator voltage drop. This will make for faster charges.

Congrats on uploading an image. -Steve

[rigspelt]

Which 55 amp alternator are you using? I have a note which says that Don said that the manufacturer of the one MMI sells recommends not to use an external alternator, but I have not looked into the ins and outs of that tip yet.

[knitchie]

A few updates...
I will move the Regulator Power from the battery to the Switch Common post.
The ampmeter will be moved prior to the Regulator Power, power to the engine switch and DC circuit board so I can measure momentary net draw.
I also omitted the fact that I will have a solar panel controller feeding the isolator as well as the alternator. This is what drove me to include the isolator in the first place since I wanted to be able to charge both batteries and not mess with manual switches to avoid drawing power from both batteries all the time.
Finally, Rigs is right, I have Don's 55amp alternator and will need to get it converted by removing the internal regulator and diodes before connecting the external regulator.

Thanks for the advise,
Ken

[High Hopes]

We still have some work to do. Here is a snippet from the XAR instructions.

The RED wire
enables the regulator to monitor
battery voltage -- and must
always see the battery being
charged. When using an isolator,
the RED sense wire MUST connect
on one of the isolator's output
terminals. If using a dual-output
alternator, the RED wire must
connect to one of the alternator
output posts. If battery banks are
unequal in size, we recommend
the RED wire be connected at the
larger battery bank.

The solar charger adds a complication as well. They like to see the battery, too, and not go through the isolation diodes. Now you have two controllers working the same battery(ies). Hmmm....

Are you stuck on using the XAR unit? Life may be simpler without it.

BTW, you don't have to modify your alternator's regulator, just insert a diode where the outside strap is on the back of the housing. A shop could do this for you.

For $80 you can get a solar panel controller that works both batteries.

[msauntry]

Steve,
The diode to the alternator you mentioned...

I've got the Mando 55amp alternator (internal reg) that Moyer used to sell. I'm getting 14.2 out of it and I'd like to bump it up a bit. Would the diode work for this?

It only has two wires: excite and batt. (ground through case)

Thanks,
Micah

just saw your edit reply... I'll look for an "outside strap". I think there was a black wire going to something on itself.

I haven't messed with diodes much. If I want a .5 volt bump, is that doable?

[High Hopes]

Depends,

Silicon diodes are around 0.7 volts. But I know the MMI 55 amp alternator only jumped up about 1/2 volt when the battery voltage sense strap was removed. I suspect that most modern alternators also have an internal limiting circuitry to establish a maximum output voltage.

For knitchie's case, he can select a diode that matches the voltage drop of the isolator diodes. That would make all things equal and allow him to still use the regulator internal to the alternator. That is, the alternator would sense 12.6 volts when the output is actually 12.6 + 0.7 = 14.3 volts, where 14.3 volts is needed to overcome the isolating diode voltage drop.

But, for your case, I'm not sure this is a good idea. If you insert a voltage drop into feedback loop, you can trick the alternator into upping its voltage. Unfortunately, this will also be true when the batteries are fully charged so you will end up overcharging the batteries. The alternator will think the batteries are low, when they aren't. I wouldn't try this if I were in your shoes.

Steve