Alternator To House Bank Or Starter Battery?

As I close in on the final configuration of my DC charging system, I have found myself without the use of my generator to charge batteries at anchor (my fault... fixable for $$$, but setting aside for the season). Currently, the alternator's output only jumps down to the starter lug for charging only the starter battery. I have read a lot of people's posts (mostly sailors) where they have the alternator charging the house bank while underway with a Balmar trickle charger over to the starter battery. Considering that I already have a Duo Charger (found one at the consignment store), I was thinking that this might be more ideal of a setup for Skinny Dippin' until I get the genset back up to snuff.

Now, as a follow-up question, could this setup (without the Duo Charger) be setup as switchable? That if desired, the alternator be routed to EITHER or BOTH the house and starter batteries? (I understand you could not do it while underway without, possibly, a field coil switch because a no load situation is bad for an alternator.)

Opinions?

Tom-

I hope this helps.This is how I do it and I have never used an onboard genny.

What device is that?

One of these?

ProIsoCharge Series Intelligent Alternator Distribution System

GonzoF1 said:

What device is that?

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A battery isolator.I prefer marine spec,even on RVs, as they don't have as much issues with humidity as automotive grade.Maybe it's just me being paranoid,but I think they are sealed better and use better quality internals.

Just to add.Size them a little larger than your alternator's max output.Say your alt puts out 100 amps use a 130A or even better a 150A.

A good overview of how they work.

Battery Isolators and Automatic Charging Relays

GonzoF1 said:

One of these?

ProIsoCharge Series Intelligent Alternator Distribution System

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That's a good unit.

On my Senator I had two 8D batteries and the alternator couldn't keep up. It was a slam dunk to hang another alternator on the Perkins as the crankshaft already had an unused pulley up front. The new alternator was a single wire installation. I now had an alternator for each battery and/or a spare in emergencies. The generator cranked from the Perkins starting battery.

But in answer to your question. There's no reason you can't use the generator's 120vac to run a battery charger to charge your boat batteries. I have a dual output, 10 amp each, battery charger hooked up to the batteries for shore power or generator charging. This keeps both my batteries topped up while using 12 volt stuff on shore power.

I also have a Freedom 30 system which is totally isolated from the house and starting batteries. I charge the Freedom battery only while running the generator (or on shore power). Works just fine.

There's many fancy systems out there, but I prefer to keep things simple. I use a Yandina combiner which mechanically combines two batteries anytime there's a charging voltage applied to either, whether the charging source is the battery charger or the alternator. It can be wired (single wire) to force combine (for emergency engine start) or force open (to apply all charging current to a single battery).

Combiner 100 Sheet

You could put one between your house and starting batteries, and even another between your generator and house or starting battery and charge all batteries from any single source whether it be your main motor, generator 12vdc, generator 120vac or shore power (battery charger).

Jeff, my generator is broken... I think you may have missed that.

ben2go said:

A battery isolator.I prefer marine spec,even on RVs, as they don't have as much issues with humidity as automotive grade.Maybe it's just me being paranoid,but I think they are sealed better and use better quality internals.

Just to add.Size them a little larger than your alternator's max output.Say your alt puts out 100 amps use a 130A or even better a 150A.

Click to expand...

A battery isolator is "old technology". It works using large diodes to keep the batteries seperate. The problem is the .7 volt (more or less) voltage drop through the diodes doesn't allow the batteries to charge fully.

Much better is a "battery combiner", also known as a "voltage sensing relay" or "VSR". A VSR senses the charging output of the alternator and when present, connects the batteries together through a relay. When there is no charging output, the relay drops out and disconnects the batteries (or banks) from each other.

This is one example: Combiner 160 Sheet

edit: I see Jeff pretty much already said what I said. It works. That's what I used on my previous boat and it's what is on HIGH COTTON although it's a brand I've never heard of.

rwidman said:

A battery isolator is "old technology". It works using large diodes to keep the batteries seperate. The problem is the .7 volt (more or less) voltage drop through the diodes doesn't allow the batteries to charge fully.

Much better is a "battery combiner", also known as a "voltage sensing relay" or "VSR". A VSR senses the charging output of the alternator and when present, connects the batteries together through a relay. When there is no charging output, the relay drops out and disconnects the batteries (or banks) from each other.

This is one example: Combiner 160 Sheet

edit: I see Jeff pretty much already said what I said. It works. That's what I used on my previous boat and it's what is on HIGH COTTON although it's a brand I've never heard of.

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True.I guess I should get with the times.I own a computer.Maybe I should use new tech in my boat also.

The ProMariner I linked to above claims zero voltage loss.

You never want a battery isolator on your charging system. Don't make this too complicated. Have the alternator charge the house bank and connect an echo charger between the house bank and the starting battery. Most Xantrex products are horrible but their echo charger is actually very good. You won't ever have to remember to switch anything and you won't have to but any expensive equipment to accomplish the same thing. Chuck

Electrical is FAR from my strong point so....I have a Perko batt switch in my lower helm. I usu. run it on BOTH when underway for the first few hours and then switch back to "engine" only. I don't use my house bank very often though. (mainly just lights, radio, anchor drag etc.) Somehow the PO had managed to kill two 8Ds in less than 2 yrs, I assume it was due to having the shore power running the old Guest batt charger all the time? Is there anything wrong with doing the way I am now? I don't even have shore power at my dock now. I have replaced the 2 8Ds with a group 31 (starting) and 2 Trojan 105s (house) last month.

twiisted71 said:

Electrical is FAR from my strong point so....I have a Perko batt switch in my lower helm. I usu. run it on BOTH when underway for the first few hours and then switch back to "engine" only. I don't use my house bank very often though. (mainly just lights, radio, anchor drag etc.) Somehow the PO had managed to kill two 8Ds in less than 2 yrs, I assume it was due to having the shore power running the old Guest batt charger all the time? Is there anything wrong with doing the way I am now? I don't even have shore power at my dock now. I have replaced the 2 8Ds with a group 31 (starting) and 2 Trojan 105s (house) last month.

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Anything wrong with the way you're doing it? No, but you are doing it the hard way. The combiner makes this all automatic.

I agree with Chuck and Ron. Go with the combiner to make it all automatic and you'll never regret it. Forget to combine or isolate the batteries one time with manual switches and you'll wish you spent the $100 for the combiner.

It's an inexpensive, fool-proof, modern solution to a problem that's been with us since we learned to use batteries. In many ways, it's a no-brainer.

While you're at it, add a quality battery monitor to ensure all is well with your batteries. It will save you big bucks in premature battery failure/replacement.

DON'T go with old-fashioned combiners and VSRs ! That approach effectively locks you in to using the same battery technology for both House and Start banks, since combiners will simply apply whatever charging profile you have for the House bank to the Start bank. You have a DuoCharger so why not use it or get another on ebay: inexpensive and allows you to replace your Start battery in the future without constraints, to battery type suited to brief, high-current loads which are completely different to deep-cycle types. I agree with the battery monitor comment: really an essential piece of kit. I'd recommend the Victron BMS series