Adding A Starting Battery

[Maine Sail]

Next question: Are all alternators considered self-limiting?--or only those with internal regulators? I should buy a copy of the standards.

I don't know of any that are not self limiting and they all come with a max output rating. There are still many boats out there with "generators" of which some are not self limiting hence the standards addressing the "self limiting" language. Some older alts did not publish an amperage or stamp it on the case so it would be a crap shoot trying to figure it out it's limited capability but any alt shop could test it for max output so you'd know.

My banks are fused at the positive terminals, well within 7", and I replaced the barbed wire with 4/0 AWG Ancor Marine (though I misplaced my lug crimpers, so I scotch taped the ends to the terminals--that's ok, right?--just until I locate my crimpers?)

If you run out of Scotch tape I like Juicy Fruit Fruit Stripe gum the best. Really keeps the moisture out..

I'm with ya on the dilemma of sacrificing the alternator versus burning down the boat. But I rarely motor, and my solar panel takes care of most charging needs here in Southern California. If I ever really used the alternator, I'd probably sheath that 4-foot 6 AWG and remove the fuse.

All that really matters is that you are confident the cable will never chafe through and create a dead short to ground.

I have seen my fair share of SCARY wiring. Doing a full re-wire right now on a boat where the largest wiring used was 16GA for domestic wiring and 4GA for the battery circuits. The 80A windlass was wired with 42 feet of 8GA wire! No wonder the jacket was melted!! Every crimp on the boat was done with pliers and over 80% of them pulled right out with less than 10 pounds force. There was no over current protection except for breakers. Expensive instruments were protected by a 15A breaker.

If boats like this survive then what you guys are doing you'll have no issues.

Builders run the alt the way they do because it saves them an extra fuse and some wire length. Using the starter cable as your alt charging circuit is a cheap way of avoiding multiple fuses, extra wire etc. etc..


Here is the federal law E-11 takes it's guidance from:

"FEDERAL LAW

183.460 - Overcurrent Protection: Special Applications

(b) Each ungrounded output conductor from an alternator or generator, except for self-limiting alternators or generators, must have a circuit breaker or fuse that has a current rating that does not exceed 120 percent of the maximum rated current of the alternator or generator at 60° C.


The output of alternators or generators (AC or DC) must have overcurrent protection as described in 183.455. This must be by means of a circuit breaker or fuse rated at no more than 120% (1.2 times) of the maximum rated output current of the alternator or generator. As this output rating may be temperature sensitive, a 60° C (140° F) temperature is used as a standard (see Figure 27). The only exception to the breaker or fuse requirement is for "self limiting" alternators or generators. These are devices that are designed and manufactured to provide only a certain maximum output no matter how much load is applied (i.e. they cannot be overloaded). This information must be obtained from the alternator or generator manufacturer, or may be available on the nameplate."


In Practice: You have a 100 amp alternator and an alternator wire sized properly to handle all those 100 amps. Even with full field voltage applied your alt will never exceed 100A then you don't need an OCPD at the alt end. Any rated alternator, 35A 50A, 75A 150A etc. should only put out it's max rating so it is therefore current limited.

With a non current limited device, that could exceed the wires ampacity rating, if full fielded or "runaway", you'd need OCP..

 

[Tom Metzger]

Builders run the alt the way they do because it saves them an extra fuse and some wire length. Using the starter cable as your alt charging circuit is a cheap way of avoiding multiple fuses, extra wire etc. etc..

People who rewire boats professionally wire it the way they do for the opposite reason - using multiple fuses, extra wire etc. etc.

YMMV

 

[Maine Sail]

People who rewire boats professionally wire it the way they do for the opposite reason - using multiple fuses, extra wire etc. etc.

YMMV

Actually I do it for the opposite, to save customers money. If your not prone to making mistakes then you clearly don't need to do this.

One of my customers fried his diodes two years in a row despite having a label made up to put right above the switch. Their switch was in a blind location so easy to mess up, and they did. After $350.00 in alternator repairs he spent the $60.00 so it would not happen again.. This was even after he bought a ZapStop which had already been toasted during one pass through off, so that would have been three passes through OFF on one boat with the motor running in two years. These were not dumb folks but they just had a really bad switch location.

I am actually re-wiring a Sabre right now where the owner is comfortable leaving the alt where it is and just adding the ACR, it is staying on the starter wire. Nothing was fused however so the batts are getting protected as well as the panel feed wire.

On another boat the owner is not so comfortable as he has toasted the alt in the past so he has asked for "protection" and has chosen an Echo Charger anyway which requires running the alt to the house bank.

I wire them ten ways from Sunday but also get to see which ways are reliable over the long haul across many installations. Some folks are just not good about the "pass through off" and some are. People with kids always tend to blame it on them.. My buddy Mike who owns an alternator repair shop loves boating season and will have a pile of diode repairs come early June...

 

[lbertran]

One More Question

I'm getting close to completing my project to install a dedicated starting battery which is going well thanks to the great guidance given in this thread. I do have one more question. I'll be installing a Deka Group 24 marine starting battery. I know I should be worried about over charging it when combined with the larger deep cycle house bank and in shore power mode. So I'm thinking of wiring so that the ACR only combines when the charge is coming from the alternator and leaving the Battery charger only on the house bank. Any cautions or concerns? Thanks!

 

[Tom Metzger]

Laura - With a grp 24 start battery and 260 ah house bank you can't go too far wrong whatever you do. Initially, you can keep a closer eye on electrolyte levels to see if you have a problem, but I don't think you will.

I would wire it according to how I use the boat. Being on shore power most of the time and getting most of my house bank charging from the 100 amp alternator as I return to the dock I only charge the start battery while on shore power. The charger spends the overwhelming majority of the time in float mode, so no overcharging. My start battery doesn't need to be charged while away from the dock, generally for less than a week at a time.

If I spent most of the time on a mooring or the hook I would charge it with both the alternator & the charger. The recharge time won't be that much different in terms of over charging.

 

[Maine Sail]

I'm getting close to completing my project to install a dedicated starting battery which is going well thanks to the great guidance given in this thread. I do have one more question. I'll be installing a Deka Group 24 marine starting battery. I know I should be worried about over charging it when combined with the larger deep cycle house bank and in shore power mode. So I'm thinking of wiring so that the ACR only combines when the charge is coming from the alternator and leaving the Battery charger only on the house bank. Any cautions or concerns? Thanks!

Laura,

You won't over charge your start battery with a combiner. If your shore charger does float you'll be fine too. No need to overthink the ACR they work well.

 

[lbertran]

ACR and Charger

Thanks Tom And Maine Sail. This project has been a great learning experience and has involved a lot of middle of the night thinking instead of sleeping. I guess it's time to stop over thinking and just get it done.