Overload Protection

[Paul]

After purchasing our '78 Trojan, it didn't take long to realize the the DC electrical system was not designed with spending time on the hook in mind. Since the boat was to undergo a stringers up restoration, I took this opportunity to upgrade the DC system as well. I started at the fuse block by isolating the cranking battery to be responsible for running only the engine, gauges and nav lights. The remaining loads were shifted over to an isolated house bank. I also added an extra fuse block to handle the extra loads that would be installed. Wire sizes were chosen installed based on amp load and length of wire.

As for the house bank, I started with a power audit of all of the DC loads on this boat, I determined that 2 T-105 batteries would be sufficient to handle the job of the house bank. The cranking battery is 750 cca. For charging these batteries while on the move, I upgraded the stock 30 amp alternator to 70 amp and added a 70 isolator for charging both banks.

Now that you know how my system is set up, my question is this. Should I have a fused link between the alternator and the isolator? I have ignition protected fuses for each battery on my AC battery charger but not on the alternator. The alternator is the GM 1 wire type.

Any thoughts?

[Big D]

I would fuse it with one rated for alternator max rated output in case of a failure. I trust you beefed up the charge wire to handle double the current. And finnally, why an isolator? These days, a much better way to go is with an ACR. Doesn't have the inherent voltage drop of diodes (which unless delt with properly means inefficient charging), and has some useful options, like emegency parrallel at helm etc.

[prowlersfish]

I would go above the rating of the alt . 70 amp alt maybe 80-100 amp breaker max. Asumine you upgraded the Wiring to handle it The resone I said over is to keep from triping it on max load , like when starting it with a real low battery.

[randyp]

I'd fuse the link, but suggest you check out the ACR set up suggested earlier. That's the route I went. It monitors the dedicated house bank (2 group 30s) and the single engine bank (1 g 30). The ACR keeps tabs on both banks and never lets the house bank drain off the engine bank so I never have the issue of a failed engine battery (unless the battery is bad). I use WalMart Maxx Marine Batteries and change them out every 4 years. Never had a problem with them. I have the stock 30 amp alternator on the 318 and there are times I wish I had a larger one, but I also use a portable Honda 2000i generator when out for more than 2-3 days from the dock and dock power. For extended crusing I found the 30 amp alternator was fine for charging the whole system in about 5-6 hours at 1800 RPM.

[Paul]

Big D, I went with the isolator simply because I'm familiar with it since I had installed the same set up in my previous boat. Also I had the alternator built to overcome the voltage drop across the isolator. I believe it was about 0.7volt. You and Randy both mentioned an ACR which I'm not familiar with. Can you please enlighten me on this. Is it one of those smart charge setups for the DC system? Are they expensive?

And yes, the wire gauge for the alternator lead can carry allot more current than I'll ever throw at it so I think I'll take Paul's suggestion and add an 80 amp fuse or breaker to it.

Sounds like a good winter project.

Thanks for the help

[Big D]

ACRs (automatic charge relays) are either electromechanical relays or electronic units that monitor the voltages of two banks. When it detects a charging voltage, it parrallels both banks for charging with no voltage drop!! When the charge disapears, it opens the circuit thus isolating the banks.

It is much easier to install since you're not changing any of the existing charge wiring (unless increasing charger output). With an isolator, you should be redirecting the alternator charge wire to the isolator instead of the starter terminal, then adding charge wires from the diodes to the banks (one back to the starter). With the ACR, you're simply adding a positive wire from each bank to the ACR, and a negative wire. With a remote switching option, you would run small control wires to the helm and have the ability to parrallel the two banks manually in case one goes dead. Another option is the ability to set the voltages at which the unit kicks in and out.

You've done it right by adjusting alternator output. Does the isolator have one, two or three diodes? it's .7 volts per diode. Be careful with the final voltage reaching the batteries so it's not too high. **Be diligent at monitoring battery voltage. When a diode fails and shorts, you'll be pumping more voltage through than some sensitive equipment will handle. By the time you see it on a meter though, it may be too late.

[randyp]

Paul. Check out info on ACRs at blue seas systems. Google it for website, etc. Cost is under $200. They have wiring diagrams, etc. and a very knowledgeable tech staff available on line or via phone to answer your questions.

[ready123]

Paul. Check out info on ACRs at blue seas systems. Google it for website, etc. Cost is under $200. They have wiring diagrams, etc. and a very knowledgeable tech staff available on line or via phone to answer your questions.

I agree they are v. helpful and I used email. Don't ignore the battery man guidelines though...
I did not use it because my GSM battery supplier did not like me linking the house battery with engine battery for charging from alternator while underway.... so use a battery switch after starting and charge the house only while underway. Were the batteries same size and type he did not have a concern for charging in tandem using ACR.
That choice has served me well as my GSM holds full charge all winter stored outside..... and the starting battery lives well off genny charging while on hook.
Just another option to think about....

[Paul]

I looked into the ACR and compared it to a diode isolator. they both have pros and cons.

PRO The diode isolator is a potted solid state unit that can charge and isolate 2 battery banks without any switching. CON It does however involve the addition of heavy gauge wiring and creates a voltage drop across its terminals. The alternator has to be set up to overcome the voltage drop.

PRO The ACR isolator requires less heavy gauge rewiring and has no voltage drop across its terminals while charging multiple banks. CON It does require a switching circuit and has solenoids which are one more thing that can go wrong.

All good info to know. I guess it boils down to personal preference. If I didn't already have an alternator built to overcome the voltage drop, I would consider an ACR installation.

Micheal, are you saying that you switch the cranking battery out of the alternator charge while the engine is running? I'm just wondering because I was told that doing this could easily "smoke" an alternator. Does it depend on the type of alternator?

[Paul]

I found a simple solution to adding overload protection to my alternator circuit. Blue Sea makes a "terminal fuse block" that will bolt directly to the alternator lug on the isolator. The wire then bolts to the fuse block.

This thing is ignition protected and can be fused from 30 to 300 amps. I'll be fusing it for 80 amps.

Again, thanks for the help.

[Big D]

I know which fuses you're talking about Paul. I think those are great.