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Old 12-20-2018, 07:40 PM   #1
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isolator vs battery switch for generator

My generator (Westerbeke 4.4kw) currently has its own start battery, which is only charged when the 115v battery charger is working. So in theory, if I goof and accidentally discharge the main engine start battery and the house battery, I can still start my generator and recharge everything. I'm thinking that it is kind of silly to not to add some charge to the generator start battery while I am mindlessly cruising along for several hours. One option would be to install an isolator in the middle of a new cable connecting the house battery to the generator start battery. Another option would be just a simple on/off switch in the middle of a new cable connecting the house battery to the generator start battery (I could turn it on after lunch, then turn it off at the end of the day). Any thoughts?
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Old 12-20-2018, 08:53 PM   #2
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I would use a small AC battery charger/maintainer for your gen battery. This way it’s always fully charged and there is no chance for error. You could use a smart ACR for combining purposes or a DC to DC charger. I would not recommend going with a standard ACR or a manual switch.
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Old 12-20-2018, 09:01 PM   #3
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Originally Posted by seattleboatguy View Post
My generator (Westerbeke 4.4kw) currently has its own start battery, which is only charged when the 115v battery charger is working. So in theory, if I goof and accidentally discharge the main engine start battery and the house battery, I can still start my generator and recharge everything. I'm thinking that it is kind of silly to not to add some charge to the generator start battery while I am mindlessly cruising along for several hours. One option would be to install an isolator in the middle of a new cable connecting the house battery to the generator start battery. Another option would be just a simple on/off switch in the middle of a new cable connecting the house battery to the generator start battery (I could turn it on after lunch, then turn it off at the end of the day). Any thoughts?
Rather than use an on/off switch I would use a 12V continuous duty relay and tie it into your ignition switch so the relay will be energized with key on and will break the connection when the key is off. You won't need to remember to turn the switch on and off. The relay will be working when you are running the engine and off when the engine is off. 12V relays are cheep. https://www.amazon.com/CONTINUOUS-SO...62773433&psc=1
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Old 12-20-2018, 09:25 PM   #4
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Another way is charging your genset battery via a small dedicated solar panel. A 25W panel with a basic regulator to the 6D/135AH sealed battery has worked well for 5 years. It overcomes the "not running not charging" issue,keeps the genset batt independent, and charged for starting the genset.
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Old 12-20-2018, 09:38 PM   #5
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How long do you go not using your generator or being on shore power?
That's the critical question. More than a week or two? Think about it, have you ever left a car for a month without charging? If the battery is not already near death, the car starts right up. Same with generators, as I experienced first hand myself with a boat on the hard and unpowered.
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Old 12-20-2018, 09:49 PM   #6
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If you wish to pursue this I would suggest an oil pressure switch of about 20-25 psi which then operates a continuous heavy duty relay. Then when the engine is running the oil pressure sw. will activate the H.D. relay allowing the gen. battery to be charged.
I'm suggesting a somewhat higher than normal activation pressure so the connection is likely broken when the engine is idling.



I would not use a manual switch. Eventually you will forget, either leaving it on or off.

Caltexfranc has a point also, a good one.
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Old 12-20-2018, 10:23 PM   #7
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Doesn't your generator have a alternator on it that charges that battery? You should be able to let it sit for months without needing a charge. (as long as nothing else is connected to that battery) I just started my generator tonight for the first time in 3 months and it started right up.
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Old 12-21-2018, 06:30 AM   #8
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All good advice but post 7 hits it on the head. You may be overthinking this.
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Old 12-21-2018, 06:36 AM   #9
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"Rather than use an on/off switch I would use a 12V continuous duty relay and tie it into your ignition switch so the relay will be energized with key on and will break the connection when the key is off."

This is easily done by installing an ignition switch with an "acc" terminal.

It will cut off when the key is being used to start the engine , and of course when the ignition circuit is off.

This is the system used to charge a RV house batteries , seamless and almost idiot proof.

Under $14.00 for a 150A relay seems a good deal, even if a $ 19.00 4 position key switch needs to be installed .

http://www.partdeal.com/wiring-elect...iABEgLDJfD_BwE
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Old 12-21-2018, 08:04 AM   #10
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Some gensets don't have a 12V charging alternator. The easiest way to charge its starting battery underway and keep it isolated is a battery isolator (diode based) or better a battery combiner like this one from Yandina: Combiner 100 Sheet.

The combiner is a better solution as it doesn't have the voltage drop of the diode type isolator.

A switch would be easy to install but can be forgotten. The isolator/combiner solution is a set and forget solution.

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Old 12-21-2018, 08:46 AM   #11
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I got rid of our Genset battery to make more room for house bank. We ha twin engines so 2- 4Ds for engines and 8- 6volt for the house. I like the simplicity of an ACR. The engine batts are isolated from the house by an ACR.
You could put an ACR between you engine and Genset battery. This would kelp Genset Bart charged underway and isolate it from engine batt at 12.75volts so it always ready
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Old 12-21-2018, 08:50 AM   #12
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https://www.bluesea.com/products/762..._-_12V_DC_500A
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Old 12-22-2018, 07:25 AM   #13
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"The isolator/combiner solution is a set and forget solution."


As is the solenoid and key switch , at perhaps 1/5 to 1/10 the cost.
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Old 12-22-2018, 08:14 AM   #14
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I also would recommend the simple 120VAC battery charger. To me, the generator is the fallback position. Should something happen and I find the other batteries discharged, I can start the generator with its totally independent battery, and run the main battery charger(s).

I have been extremely happy with these (have2).

https://www.batterystuff.com/battery...arger-rs1.html

Something simple like this would work well also.

https://www.batterystuff.com/battery...-021-0123.html

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Old 12-22-2018, 08:28 AM   #15
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Doesn't your generator have a alternator on it that charges that battery?.

Not all do. Mine has one and I am planning on bypassing it.
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Old 12-22-2018, 09:26 AM   #16
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The spec sheet for the Westerbeke 4.4 kw generator says it has a 12 volt 10 amp battery charging output that you can wire to the start battery.


https://www.westerbeke.com/advanced%20specs/4.4_bcd.pdf
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Old 12-22-2018, 09:42 AM   #17
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The spec sheet for the Westerbeke 4.4 kw generator says it has a 12 volt 10 amp battery charging output that you can wire to the start battery.


https://www.westerbeke.com/advanced%20specs/4.4_bcd.pdf

Very interesting. Up until now, I had no idea that existed. Thanks very much.
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Old 12-22-2018, 11:32 AM   #18
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I would think that the alternator is already connected to that battery and you just don't realize it. Turn off the battery charger that is attached to it and take a reading of the voltage at that battery. Start the generator and take another reading of the voltage at the battery. If the alternator is charging the battery it should read about 13.5 volts or so. Don't wait to long to test it. Problem solved. You either need to wire the alternator to the battery or do nothing as everything is working as designed.
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Old 12-22-2018, 02:43 PM   #19
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Not all do. Mine has one and I am planning on bypassing it.
Why would you do that?

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Old 12-22-2018, 04:11 PM   #20
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Why would you do that?



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Just so I can be told on an online forum how wrong and stupid I am. :-) lol
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