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Old 08-17-2017, 07:13 PM   #1
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Isolator question

My newish to me boat.. a Carver 350 Voyager.. has twin Volvo TAMD41B engines with a Valeo Rhone alternator on each engine, 51 AMP internally regulated. Both alternators are connected to a Sure Power isolator with two input terminals and three output plus two smaller terminals for which I know not. The two input terminals read 14.68 volts and 14.66 volts. and the two output terms read 13.83 and 13.85. essentially a loss of .8 volts. The other output terminal reads 14.40. This cable is connected to nothing. I suspect that this third cable may have been connected to the generator battery. The main battery bank is about 600 amps. (6 6 volt golf carts)

I am concerned that batteries are not getting charged sufficiently with voltages of 13.85. What I am proposing is to connect the output cables to the input and thus charge at 14.6...basically join the output to the input on both alternators as an interim measure. I understand that the strongest alternator may overcome the other one when they drop out of bulk. I have tried this on one of the alternators and it seems to work as thought with 14.XX volts showing on relatively full batteries. The only issue that comes up is that in the absence of the isolator there is battery voltage at the positive terminal of the alternator. Can this be/cause a problem? So far I have just tried this on one of the alternators.

My ultimate goal is to upgrade one of the alternators to 100+ amps with an external regulator but due to confined quarters can only fit a 5" or 6" max alt, which limits me to around 120 amps or less. I was thinking one of the Leece Neville MR series with a Balmar ARS5 regulators. It would be nice to use one of the new Balmar 6 series alts, but with the regulator I'd be on the wrong side of $1000. with tax. Any alternative suggestions would be welcome.

This seems like a very complex boat, electrically, with automatic relays and automatic transfer switches with very cramped access. I just had to replace the Xantrex Freedom 2000 inverter/charger with a Magnum ME2125 and remote because the Xantrex gave up the ghost.

Ian Munro
Seattle
M/V Odyssea
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Old 08-17-2017, 07:19 PM   #2
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Sounds to worth just replacing the isolator with a better combiner.

This one's very robust

https://www.bluesea.com/products/762..._-_12V_DC_500A
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Old 08-17-2017, 07:43 PM   #3
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I am a little confused. You have a 2 input 3 output diode isolator which feeds two battery banks. If you were to connect the two alternators directly to the batteries you would lose isolation. If you ran the house bank down at anchor, you would also run the starting battery down and then couldn't start the engine.

That is why you have isolators, but as you note they also have a significant voltage drop. A combiner or ACR will solve this problem. But you also say you have an automatic relay and transfer switch. What does this do? You could probably use this one ACR to handle all of your battery combination and isolation needs.

It sounds like you have an electrical system that was cobbled together with no overall plan. I would find a good marine electrician to come up with a comprehensive plan to deal with your electrical system.

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Old 08-17-2017, 08:07 PM   #4
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Before playing with the connections I would recommend you to get the install manual for your isolator, read it and understand what is the purpose of each connector on it. The voltage drop you are measuring between input and output is certainly due to the diode used for isolation.

L.
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Old 08-17-2017, 08:30 PM   #5
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Isolator Question

"That is why you have isolators, but as you note they also have a significant voltage drop. A combiner or ACR will solve this problem. But you also say you have an automatic relay and transfer switch. What does this do? You could probably use this one ACR to handle all of your battery combination and isolation needs."

There is just one bank of batteries... no starter bank... and a totally separate generator battery. Theory being if house bank goes flat I can start the main engines with a charge from the generator. The automatic transfer switch is for transferring from shore to generator. The automatic relay is for selecting one of two shore power stations. On previous boat I had a rotary switch to go from shore power to generator and just one shore power point. I cannot afford to throw money at this boat by hiring $100. per hour electrician which is why I am trying to understand the systems myself.

My concern is if the pos. post on alternator is live is that going to cause a problem with drawing down the battery or other problem? Most combiners that I have investigated seem to address two or three battery banks.

It doesn't appear that the system is cobbled together, just more complex than I am used to.

Thanks for your response.

Ian
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Old 08-17-2017, 10:31 PM   #6
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Well, you certainly confused me by talking about AC and DC systems in the same breath. Yes, maybe not cobbled but certainly complex. An automatic AC switchover system is more complex than 99% of the boats on TF.

Pay a good electrician a few hundred dollars to explain how your systems work. Then if you need to make changes then DIY.

Complex electrical systems are almost impossible to explain and diagnose on a forum like this.

David
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Old 08-17-2017, 10:43 PM   #7
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"Theory being if house bank goes flat I can start the main engines with a charge from the generator."

If it were me, I would change this sooner rather than later. The last thing you need is a cranky generator killing your chances of getting back to port. I would use 2 cranking batts and if you have to save space then let the genny crank off of one of the main engine batts (not the other way around as it is now).
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Old 08-17-2017, 11:51 PM   #8
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The only issue that comes up is that in the absence of the isolator there is battery voltage at the positive terminal of the alternator. Can this be/cause a problem? ------------------------NO!. not unless something else is haywire. Absolutely normal in a system without isolators. The diodes inside the alternator stop the batteries from discharging when the alternator is not running unless that alternator is also haywire. DOes happen but not often unless someone has been playing with battery switches going through the OFF position with the engine operating.

Yes, isolators drop approx 0.7 v . ACR drop a few millivolts, maybe 0.010 V. so far less which is why they are supplanting the isolators. The ACRs also have some electronics for controls to connect/disconnect at appropriate voltages to protect the house /starter banks. It sounds like your system was done a long time ago or someone was locked into isolators as the best way when not really.

Often twin engine systems are set up with one alternator to charge the house bank. The other alternator charges the dedicated engine starting bank. This would also be the case with a single engine driving two alternators.

Then use a cross over switch between the house bank and starter bank if the starter bank fails so the house bank can be brought into play.

Usually the house bank has a much higher capacity output alternator and uses a dedicated aftermarket alternator controller, your Balmar or similar, to run a 3 stage charge regimen on the house set.

The other smaller alternator is used to recharge the starter battery[s] using what ever regulator is built into that alternator. Since engine starting, sompared to house loads, uses a comparatively small actual amount of energy this setup usually works fine and that battery or batteries are recharged fairly quickly.

I'm simply trying to suggest a better and simpler setup which can work well and accomodate your intentions about better charging and how to improve what you have. I won't try to figure out what you have because as David Marchand said over the internet is darn difficult and fraught with difficulty.

In other words toss the isolators, use a dedicated starter bank, use the two alternators to charge each bank separately, use an isolation switch between the two banks for emergency use, upgrade the alternator and controller for the house bank when budget and inclination allow.
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Old 08-18-2017, 06:48 AM   #9
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Toss the transistor Isolator and spend $18.00 for an RV solenoid .

This will merge the start batt with the house with almost no voltage loss.

KISS
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Old 08-18-2017, 12:29 PM   #10
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Isolator question.

The only issue that comes up is that in the absence of the isolator there is battery voltage at the positive terminal of the alternator. Can this be/cause a problem? ------------------------NO!. not unless something else is haywire. Absolutely normal in a system without isolators. The diodes inside the alternator stop the batteries from discharging when the alternator is not running unless that alternator is also haywire. DOes happen but not often unless someone has been playing with battery switches going through the OFF position with the engine operating.

Thank you...that's exactly what I wanted to hear and will get me thru the rest of the summer when I can figure out a more permanent solution.

Lou: I did just that...found the datasheet on the isolator and decided that it was miss-applied in my application.

FF: I'll have to look into that

Thank you all for the time and effort you all put into this. I was feeling a bit overwhelmed because Vacu-Flush stopped working properly; the battery charger/inverter stopped working and I found that the batteries were not charging properly even with a long (8-10 hours). The head was easily fixed... just needed the know-how to replace the duckbill valves... and charging system on AC charger was replaced.

Ian Munro
Odyssea
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