isolator vs battery switch for generator

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
S

seattleboatguy

Senior Member
Joined
Nov 2, 2013
Messages
327
Location
USA
Vessel Name
Slow Bells
Vessel Make
Marine Trader 38
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?
 
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.
 
seattleboatguy said:
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?
Click to expand...

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-S...ocphy=9053944&hvtargid=pla-570362773433&psc=1
 
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.
 
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.
 
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.
 
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.
 
All good advice but post 7 hits it on the head. You may be overthinking this.
 
"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-elec...MI_7ydguuw3wIVlQOGCh2NEw6bEAQYAiABEgLDJfD_BwE
 
Last edited:
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.

David
 
Last edited:
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
 
"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.
 
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/batter...s-12v-6-amp-waterproof-smart-charger-rs1.html

Something simple like this would work well also.

https://www.batterystuff.com/batter...12v-750ma-4-stage-smart-charger-021-0123.html

Ted
 
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.
 
Tom B; I was going to ask the same things but restrained myself trying to be nice. :flowers:
 
Simply put, i have one house bank and one starter bank (no dedicated battery for generator). The starter bank starts both engines and the generator. When I start the genset at anchor, the tiny generator alternator tries to charge the large bank and gets really hot. To avoid it, I have had to build a custom battery charger profile to take the burden off the genset alternator. The rub is that the charger is in a very awkward place in the boat and the profile, unbeknownst to me when I bought the charger, cannot be changed with the “remote control” panel. So it will be easier to just bypass the little alternator that I just don’t need until I can get a new charger or find a new place to mount it. So there ya’ go.
 
If you don't have an alternator, then my vote is for a combiner like the aforementioned Blue Sea ACR (Auto Charging Relay) or the Yandina combiner.

I started with a Yandina 100 and upgraded to the 160 later when I upped my alternator. They are set-and-forget if you want that or they can be set up with a small control switch that allows control of the auto/manual functions. I chose the latter and have been very pleased.

It's normally in the auto (set-and-forget) mode but when I desire a manual parallel of the batteries to share a single charge, then I can select that function. I find this helpful with my twins allowing me to charge both battery banks from either single alternator in the event of single engine operation or from my single bank shore charger.

In either case, the banks separate when the charge disappears so the house loads can't drag down the start bank.

I have separate 1-All-2-OFF switches on the load side of the circuits to allow me to tie the banks together for jump start purposes or to share the start battery with the house loads. This has never been needed but I'm glad it's there just in case.
 
Last edited:
Tom.B said:
Just so I can be told on an online forum how wrong and stupid I am. :) lol
Click to expand...

Ah.

:)


Tom.B said:
Simply put, i have one house bank and one starter bank (no dedicated battery for generator). The starter bank starts both engines and the generator. When I start the genset at anchor, the tiny generator alternator tries to charge the large bank and gets really hot. To avoid it, I have had to build a custom battery charger profile to take the burden off the genset alternator. The rub is that the charger is in a very awkward place in the boat and the profile, unbeknownst to me when I bought the charger, cannot be changed with the “remote control” panel. So it will be easier to just bypass the little alternator that I just don’t need until I can get a new charger or find a new place to mount it. So there ya’ go.
Click to expand...

Might be easier, if you have a small space somewhere, to add a separate genset start battery? Could be some advantages to that?

But I'm surprised your alternator is getting hot, or trying to charge the larger start bank to any serious degree. Wouldn't have thought your engine start battery would take much charging, most of the time... It's not like starting your engine occasionally depletes it all that much...

??

-Chris
 
I replaced my gen batty On-Off Sw with a 1-2-Both-Off Sw.
Same foot print & mounting.
It allows me to connect gen & start/house batts if needed in an emergency... sort of a permanently available set of jumpers.
That way I can use either batty to help boost a weak one... isolators won't allow that. My AGM gen batty sits all winter in storage w/o a problem and so far I have never had to use the Sw in combine mode.... nice to have the insurance and I liked the simplicity. I do have a 120V outlet next to the gen batty and have a maintainer stored there for topping off the gen batty if unused for a long period.
 
One of the main jobs of the generator on my boat is to power the main battery charger for the house bank. There's also a secondary charger connected to the starting and genset banks. So, whenever the generator is running, all the banks are being charged, alternator or not.

Not to dismiss all the other good ideas posted above, but that's my "set it and forget it" solution.
 
Based on my experience,

kept in mind the following points:

1) The generator may have (in my case has) is own battery-charging alternator.
2) The generator starter battery does not power any appliance. The only items the battery powers besides the starter are the light in the control panel and possibly injector heaters (as in my case), all of which are used only in connection with starting the engine. In newer generators, there may be new electronic panels that draw a minuscule current from the battery.
3) The period of time the generator is producing AC in a typical run should be enough to recharge the generator's starter battery using a small 2-amp-hour AC-powered battery maintainer/charger should be adequate. In my case, the engine alternator takes care of it.
4) An AC-powered charger for the starter battery would also maintain the battery topped while at the slip or from any other AC sourve in the boat.

For the reasons above, in Sea Trek (my boat) I use a small battery (trickle) charger-maintainer. The generator has its own alternator and it does replenishes the battery during operation after starting. The only reason for using a trickle charger in Sea Trek (my boat) is to span long periods without using the generator. The trickle charger is operated either from shore AC power or the inverter, as available.

Cheers,
 
Last edited:
BruceK said:
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.
Click to expand...


This is my way of doing it.
 
'add some charge to the generator start battery while cruising along for several hours. '





1. Is the genset, start & house battery same chemistry, say flooded lead acid [fla] with similar charging voltage requirements ?




If yes then a very simple solution I have used with success is a voltage sensitive relay [vsr]


The ones I have used a "BEP VSR"



Voltage Sensing Relays | bep


sealed and designed for marine ~140amp rated. they have a led that indicates when charging.
They turn on at around 13.2v and off around 12.7 so only once the source battery starts to charge [propulsion engine] it closes. Once source battery off charge [ engine stopped ] they open. so doesn't flatten your source battery.


vsr has two studs & one thin black wire

one stud gets hooked up to source [start] battery positive and the other gets hooked up to your load [genset] battery positive with a thin wire to your negative bus.



I always put a 150A fuse in series too.


If not similar battery chemistry and or different charging requirements between the start, house battery & genset batteries then still use a vsr and a dc to dc adjustable converter




then the battery charging only gets turned on when your propulsion engine is above charging speed, and your system is less likely to flatten the start battery.



if you keep the wire under say 8 gauge max[~4mm]] then the source alternator wont work as hard and it'll reduce the initial charge current a little and so last longer.







Genset alternator overheating


is genset permanent magnet [often two wire with no fan, like a lot of small tractors] or variable field alternator [like a normal car type alternator] ?



if its permanent magnet you cant overdrive it [they actually work flat out the whole time], if its variable field yes you can over drive it.


some dc to dc devices do have a current limit option [victron energy dc to dc do and I've used them]



sing out with questions.


happy new year all and may your fishing rods have a good bend in them


Kind Regards Donald
 
You must log in or register to reply here.

Similar threads

P
Isolating batteries
Replies
9
Views
476
PNM
P
Gypsy Diver
Balmer voltage regulator vs battery isolator
Replies
6
Views
761
Bmarler
B
NWboater2
8D starting battery replacement
2
Replies
39
Views
3K
NWboater2
NWboater2
LeoKa
Auto switch for low voltage?
Replies
19
Views
1K
Patrick4002
Patrick4002
R
Battery Combiner Help/ Advice
Replies
7
Views
1K
RyanZ
R

Latest posts

Back
Top Bottom