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Old 05-27-2012, 11:33 AM   #1
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Two alternators, one battery bank

Our new to us boat has twin engines, each with a 75amp alternator. Neither alternator seems to charge the battery bank. Any issues with just connecting the outputs of both alternators to the battery bank?

Thanks,

Bob
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Old 05-27-2012, 11:43 AM   #2
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Are they one wire alternator's? If not you might over charge your batteries.
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Old 05-27-2012, 01:16 PM   #3
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Our new to us boat has twin engines, each with a 75amp alternator. Neither alternator seems to charge the battery bank. Any issues with just connecting the outputs of both alternators to the battery bank?

Thanks,

Bob
Are they charging? Probably not if they don't "feel" the battery bank. If you choose to bypass the remaining charging circuit, you can just run a heavy wire from the alternator battery post to the starter battery post. I don't suggest this, would recommend you trace/ figure out "the system" and repair it.
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Old 05-27-2012, 02:13 PM   #4
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I don't think we know enough to answer the question. Are you talking about engine alternators that charge a start battery bank but not a house bank? Or about alternators that don't charge anything?
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Old 05-27-2012, 06:23 PM   #5
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We just bought the boat and on the way from Beaumont to our Galveston Bay marina I noticed that the batteries were going down until all the electronics quit running. Anchoring out one night on the way all three batteries were dead in the morning so I'm assuming the two "house" bank batteries and the supposedly independent genset start battery are all hooked together somewhere. The plan is for one big house bank and a separate start battery for the engines and genset. This was the setup we had on our sailboat, alternator with external regulator and AC battery charger charged the house bank and an Echo Charge (SolidState ACR) unit charged the start battery.

The alternators are simple internal regulator units. So the question is, can I just parallel the outputs from the alternators? Is there an external regulator that will handle two alternators? With the much lomnger run time on a power boat I realize there is the chnace of overcharging the batteries with a dumb alternator.

Bob
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Old 05-27-2012, 06:43 PM   #6
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Bob, I'm not sure about tying the output of both alternators together. I have twins, both alternators show charge when running, and I have always assumed that they both contributed to the twin group 31 house bank/ starting batteries I run. As you are going to do, I isolated the generator starting battery to serve only it.
Have you figured out why the batteries went down?
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Old 05-27-2012, 09:58 PM   #7
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Do you know how the two alternators are connected to the batteries? I haven't had time to get into the battery hookups yet. The PO claimed that the third battery was just for the genset. Apparently he didn't know any better or he lied.

Up to this point we have been working on comfort items. Added Freon to the aft A/C, it was freezing up, replaced the three knob control with a digital control, got the fridge working, making sun screens, added shades to cover the windows, it gets hot here in Texas.

The electrical gremlins are next. I was just wondering how others had the dual alternators hooked up. Waiting for my wife to go back to work for WM before we buy any major, or even minor, items.

Hoping to get all this resoved by the end of hurricane season so we can spend Christmas in the Bahamas.

Bob
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Old 05-27-2012, 11:52 PM   #8
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Bob, I don't know how they are hooked up. I have amp meters at the upper and lower helms and I do know that without a shunt (which I have never seen) the current from the alternator has to go THROUGH the ammeter. With this much wiring- there is a lot of opportunity to lose current. I would also like to find out how two alternators supply one battery bank.
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Old 05-28-2012, 12:47 AM   #9
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There's a 100 different ways to skin this cat - you'll no doubt do what you like and what it easiest to implement. What I have done is this:

I have a Balmar external regulator that runs both alternators. The output from the two alternators charges my house/start bank. I have a Xantrex echo charger which feeds excess charge to my single genset battery which is otherwise isolated from the house system. The Balmar field circuit (what excites the alternators) runs through a normally open oil pressure switch on each engine. That way I never feed field current to an alternator on a non-running engine. Balmar makes a more expensive solution to that problem but my 2 NO switches work just fine at much lower cost. The advantage of the Balmar external regulator is that it makes the alternators work and delivers a 3-stage charge to my main battery bank.

What I would absolutely NOT do is tie the output from two internally regulated alternators to a battery bank for two reasons. First off an internally regulated alternator will deliver a small fraction of its potential output in any situation. Second by tying the two alternators together the one with the lower setpoint will cut out and you will only see the output from one alternator so you will have two alternators putting out a low single alternator output.
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Old 05-28-2012, 05:55 AM   #10
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Sounds like there is some sort of batt Merge setup you haven't found yet.

They shouldn't all die together.

You will need to look and attempt to draw a schematic of what you have , and the problem will be seen.

Neither alt charging could be there dead from the electrical setup.

If the boat was a Dock Queen , my guess is to look at how the shore power was fed to ALL the batts , at the same time.

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Old 05-28-2012, 09:24 AM   #11
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bobofthenorth, I like the idea of an external regulator driving both alternators. We've used the echo charge unit before to charge the start battery.

FF, I don't think there is a piece of paper big enough to draw up a schematic. There is a three channel charger that charges the two house batteries and the genset start battery. That may be where the problem is of all batteries dying together. That may be my starting point.

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Old 05-28-2012, 09:34 AM   #12
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FF, I don't think there is a piece of paper big enough to draw up a schematic.
Do it anyway - its really good advice. I use a little piece of free software called Dia to do my schematics. There's lots of other software that will work as well. The point is not so much the drawing as what you will learn by making the drawing.
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Old 05-29-2012, 12:43 AM   #13
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You can use two internally-regulated alternators in parallel, but it's not an optimum solution. Each regulator has a specific turn-on voltage, and even if they are from the same manufacturer, same plant, same day, they will be slightly different.
If battery voltages as sensed by the alternators at their terminal post are below the turn-on voltages both alternators produce a charge output, but they will reach a point where one reaches its charging set-point voltage and effectively idles away while the other continues to charge.
If you want true load-sharing or paralleling you have to use an externally-regulated alternator with parallel charge capability like Balmar's, but it won't hurt to connect the two like you said.
Old boats often used #10 wire from the alternator to the ammeter to the battery bank. This long run with small wire could easily result in an alternator output of 14.7v that was only 13.7 at the battery, so the batteries took a very long time to reach a full charge or were chronically undercharged.
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Old 05-29-2012, 06:10 AM   #14
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If you have cruising that does not include a dock and power hose every night , the alts should be seperaited and at least the house alt should have a 3 stage regulator. With a SOC to monitor the house bank.

You probably should consider a set of snips , and rewiring with a sensible setup that requires little to understand.

A pail full of transistorized combiners and joiners can be replaced with a simple rotary switch that ONLY needs to be moved in an emergency.

Normal ops , start drive , secure , nothing to do, seamless!

Not hard to do.

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Old 05-29-2012, 10:37 AM   #15
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Our new to us boat has twin engines, each with a 75amp alternator. Neither alternator seems to charge the battery bank. Any issues with just connecting the outputs of both alternators to the battery bank?

Thanks,

Bob
If they should be connected together, the boat would have been wired that way originally. We can assume that the alternators originally charged the batteries so rewiring things isn't the way to fix a problem.

Rather than making modifications or repairs based on what seems to be happening, I suggest finding out what is actually happening.

You can have the alternators checked, but how about the batteries? How about an electrical load that's consuming the charging current?

Find out what is causing the problem and deal with it. Repair or replace it. You won't need to rewire the boat.
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Old 05-29-2012, 11:21 AM   #16
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Find out what is causing the problem and deal with it. Repair or replace it. You won't need to rewire the boat.
Begging to differ but on the older boats that most of us have here, you very often do need to "rewire the boat". Leaving aside the fact that there have been many electronic advances since the 1980's when many of these boats were built, we also have to contend with years of ownership by people who may only have had a dim grasp of electronics and may have made the situation worse by hiring contractors who were either stupid or charlatans or both. The end result often is a boat with a lot of legacy components that either are no longer connected or worse are partially connected leaving unknown electrical pathways to contend with. Some of that stuff simply needs to be ripped out and some of it needs to be replaced.
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Old 05-29-2012, 11:54 AM   #17
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Lots of good ideas

The first thing you have to do is understand how your boat is setup, it worked for someone. Check your battery switches. Make sure they are on the proper setting. Before anybody can give good advice you need to know how the boat was set up. Most new boats charge the house bank with one engine and the starting bank with the other. Properly done, battery chargers are tied in at he battery switch's. As mentioned who knows the history of this boat. Condition of terminal ends, battery state are all players in this drama. If you don't have an understanding of your electrical system it would be good money to hire a good electrician to check out and walk you through your boats electrical system. Electrical systems are probably the biggest head ach in owning a older powerboat. They are also the largest cause of boat fires. Early this year I spent a week cleaning up the electrical system on a Albin Trawler. The owner couldn't get insurance coverage after a survey, it was lucky for her that the surveyor caught part of the problem. When I started checking out the boat I found the the shore power and ac wiring had been set up with neutrals switched shore power hooked up load to neutral, battery charger hard wired with romex, no thermal protection, So many connections on battery posts I had add a terminal strip, exposed 120 v connections, twist connectors and some with just twisted wire and electrical tape. Wires strewn without restraints cable tv style. So you really need to spend some time learning your boats electrical sysem.
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Old 05-29-2012, 12:27 PM   #18
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Begging to differ with rwidman, the boat does require some rewiring. I don't like having two house banks which are also used as start batteries. My way is one big house bank and a separate start battery. All charging goes to the house bank with a ACR or echo charge for the start battery. Worked great for us for six years cruising on a sailboat.

The original question was how to connects the two alternators. The answer seems to be an external regulator controlling the two alternators. That was the way we did the sailboat except that there was only one alternator. We also carried the original alternator and belt as spares.

I think all boats of that vintage have strange wiring problems which may have worked for the way the PO used the boat. On our sailboat there was a cable straight from the battery to the engine starter and from the engine starter to the load connection of the battery selector. So no matter the position of the battery selector, the DC loads where always connected to the battery.

Bob
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Old 05-29-2012, 08:40 PM   #19
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i am pretty sure both my alternators are wired to a bank of two starting batts, each alt wired to one batt. Since the internal regulator sense the V at the batt terminal, even the two batts are connected the V sensed is still the local batt (at least this is how i understand it..) btw house and start batts connected thru the bluesea acr which allows for charging current to be shared and also load sharing up to a set lower V shut off point.
there is no doubt using an external regulator is the better way to go for charging your batts from alternators.
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Old 05-30-2012, 06:28 AM   #20
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"I don't like having two house banks which are also used as start batteries. My way is one big house bank and a separate start battery."

Either way works , but the starter only battery set is Required for cold starts in cold conditions , no block heater.

Not usually a requirement for yachts as the engine room would need to be winterized at only 32F , not really cold.

A dual house set with start ability does work, just be sure the Deep Cycle house batts have the required CCA (yes many are also start rated on the mfg site).

To get the most out of the batt bucks , ALL the batts would be on one big bank (deep cycles) and a seperiate start batt would be on the noisemaker.

The noisemaker batt would have the CCA (probably a group 31) to start the main engine with booster cables.Safer than a rotary switch , unless its lockable.

The noisemaker would have a truck 135A belted on its front,as this is the best way to recharge the house when anchored or in an emergency.

Power boats have similar operating problems as sail boats , but many more options that optomise the boat for cruising , mostly due to more volume.

FF
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