T.R. Bauer
New member
Do you really have to have them. I have heard both.
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Twin batteries for twin engines?
- Thread starter T.R. Bauer
- Start date
The reasons for two batteries on twins are two:
1. Redundancy, so that you have a start battery for each engine, and if one goes dead, you can start the other.
2. Each motor has it's own alternator and regulator. If connected to the same battery, they sense each other's high charging voltage, think the battery is fully charged, then stop charging, then sense the now low voltage, and then start over to charge, etc., ad infinitum, in a cycle. (This may not exactly describe the events, but you get the idea!)
Joe. :teeth :thup
1. Redundancy, so that you have a start battery for each engine, and if one goes dead, you can start the other.
2. Each motor has it's own alternator and regulator. If connected to the same battery, they sense each other's high charging voltage, think the battery is fully charged, then stop charging, then sense the now low voltage, and then start over to charge, etc., ad infinitum, in a cycle. (This may not exactly describe the events, but you get the idea!)
Joe. :teeth :thup
You don't HAVE to have twin batteries, but having a spare is a good idea. Having an A/B switch to select either or both at the same time is good, so you can select between "good" battery and "dead" battery if needed.
Some alternators can be damaged if you disconnect the battery while the engine is running. Having a "make before break" switch and never selecting the "off" position while running will keep that from happening. The other kind of switch will go open as you go from A to B, but the make before break switch will momentarily go to "Both" while going from A to B.
Just don't get careless and select "off" with an engine running.
I run my #1 battery on odd days and the #2 battery on even days. It helps me remember to even out the use. Sometimes I run "both" for charging, but usually just one or the other. If I'm overnighting, at night I'll select the one that will be run the next day so it gets recharged after use overnight.
With two batteries and a switch you have an extra battery in case one dies, and it's easy to "move" the battery between engines in case one engine isn't running/charging and you're limping home on the other engine. Having an extra "house" battery would be nice, but these little boats are sensitive to extra weight, and there aren't many things heavier than batteries. It's your call regarding the tradeoff.
Most everyone agrees, though, that having at least two is an important safety factor. And a switch to isolate one or the other is important, too. With the engine(s) off, and your lights on, switch SLOWLY from A to B and see if the lights flicker, which would indicate a non-"make before break" switch, and danger to the alternator(s).
I have the make before break switch and I still don't like to switch with an engine running.....
Some alternators can be damaged if you disconnect the battery while the engine is running. Having a "make before break" switch and never selecting the "off" position while running will keep that from happening. The other kind of switch will go open as you go from A to B, but the make before break switch will momentarily go to "Both" while going from A to B.
Just don't get careless and select "off" with an engine running.
I run my #1 battery on odd days and the #2 battery on even days. It helps me remember to even out the use. Sometimes I run "both" for charging, but usually just one or the other. If I'm overnighting, at night I'll select the one that will be run the next day so it gets recharged after use overnight.
With two batteries and a switch you have an extra battery in case one dies, and it's easy to "move" the battery between engines in case one engine isn't running/charging and you're limping home on the other engine. Having an extra "house" battery would be nice, but these little boats are sensitive to extra weight, and there aren't many things heavier than batteries. It's your call regarding the tradeoff.
Most everyone agrees, though, that having at least two is an important safety factor. And a switch to isolate one or the other is important, too. With the engine(s) off, and your lights on, switch SLOWLY from A to B and see if the lights flicker, which would indicate a non-"make before break" switch, and danger to the alternator(s).
I have the make before break switch and I still don't like to switch with an engine running.....
I notice Joe just posted, too. I think he runs twin engines, and I run a main/kicker. My battery comments still hold, however.
Alternators on cars and boat engines don't really sense battery voltage and actively change charger output. The alternators are simply set to a more or less standard charging voltage (around 14 volts, plus or minus) and it's assumed that a low battery will pull more current at this high voltage, and as the battery(s) charge up, it(they) will pull less current. It's not as good for the batteries as a "real" battery charger with some intelligence, but it works. It also tends to overcharge the batteries all the time and it's good to check your water level once in a while because the constant overcharging cooks off the water.
Maybe in the last few years someone's added some smarts to engine alternators, but I haven't heard of it.
Hey, Joe, as an aside, how come your crest on the left shows three granny knots instead of three square knots? Is there a history of "challenged" knot tiers in the family? :wink
Jeff
Alternators on cars and boat engines don't really sense battery voltage and actively change charger output. The alternators are simply set to a more or less standard charging voltage (around 14 volts, plus or minus) and it's assumed that a low battery will pull more current at this high voltage, and as the battery(s) charge up, it(they) will pull less current. It's not as good for the batteries as a "real" battery charger with some intelligence, but it works. It also tends to overcharge the batteries all the time and it's good to check your water level once in a while because the constant overcharging cooks off the water.
Maybe in the last few years someone's added some smarts to engine alternators, but I haven't heard of it.
Hey, Joe, as an aside, how come your crest on the left shows three granny knots instead of three square knots? Is there a history of "challenged" knot tiers in the family? :wink
Jeff
T.R. Bauer
New member
Sea Wolf":w0cch2tw said:The reasons for two batteries on twins are two:
1. Redundancy, so that you have a start battery for each engine, and if one goes dead, you can start the other.
2. Each motor has it's own alternator and regulator. If connected to the same battery, they sense each other's high charging voltage, think the battery is fully charged, then stop charging, then sense the now low voltage, and then start over to charge, etc., ad infinitum, in a cycle. (This may not exactly describe the events, but you get the idea!)
Joe. :teeth :thup
I wonder how they got around this on my 2000 f-350 dually with twin alternators as the two batteries are shared. Maybe something higher tech?
T.R. Bauer
New member
jlastofka":bm9qzq1h said:You don't HAVE to have twin batteries, but having a spare is a good idea. Having an A/B switch to select either or both at the same time is good, so you can select between "good" battery and "dead" battery if needed.
Some alternators can be damaged if you disconnect the battery while the engine is running. Having a "make before break" switch and never selecting the "off" position while running will keep that from happening. The other kind of switch will go open as you go from A to B, but the make before break switch will momentarily go to "Both" while going from A to B.
Just don't get careless and select "off" with an engine running.
I run my #1 battery on odd days and the #2 battery on even days. It helps me remember to even out the use. Sometimes I run "both" for charging, but usually just one or the other. If I'm overnighting, at night I'll select the one that will be run the next day so it gets recharged after use overnight.
With two batteries and a switch you have an extra battery in case one dies, and it's easy to "move" the battery between engines in case one engine isn't running/charging and you're limping home on the other engine. Having an extra "house" battery would be nice, but these little boats are sensitive to extra weight, and there aren't many things heavier than batteries. It's your call regarding the tradeoff.
Most everyone agrees, though, that having at least two is an important safety factor. And a switch to isolate one or the other is important, too. With the engine(s) off, and your lights on, switch SLOWLY from A to B and see if the lights flicker, which would indicate a non-"make before break" switch, and danger to the alternator(s).
I have the make before break switch and I still don't like to switch with an engine running.....
So, you are running your twins on one battery essentially, correct? I only ask because my friend with his twin hondas in his beer can boat is only running one battery - and has not been for years. He does have a house battery too. I am starting to think what I read a good while back that it was essential to have two batteries, was bunk.
jlastofka":s03mzjhd said:Hey, Joe, as an aside, how come your crest on the left shows three granny knots instead of three square knots? Is there a history of "challenged" knot tiers in the family? :wink
Jeff
Jeff-
Thanks for the correction! I've never heard anyone fully explain the twin alternator problem fully, so have been going with my own deductive guessing senses on that one.
If you're right about the lack of sensing circuits in charging systems, this has a lot of implications for simultaneously using engine alternators, battery chargers, and other devices simultaneously on batteries, in single or parallel.
I guess it's just another example of how you can get into trouble assuming intelligence exists elsewhere when it doesn't! (I did qualify it, though, and have a single motor, FYI)
As to the granny vs square business, my "granny" was a winner, I was pretty "square" as a kid, and my crests are stolen heraldry are "knot" of my own making.
Go figure!
Joe. :lol:
T.R. Bauer
New member
So, does this mean one will really work fine? Or?
Let's see. Two engines, one battery. One engine will be at a higher voltage than the other and will put out most or all of the charging current. If the other engine has an alternator it will have diodes on its output and no reverse current should flow into it. If it had a generator instead of an alternator (were any made like that?) I suppose some reverse current would flow into it and I'd ask the engine manufacturer, but I'd guess the answer would be "OK". Mine being main/kicker means they're rarely running at the same time unless I'm doing the "twin engine" docking thing, which is fun.
A little TRIVIA-
In the my old days of as an Aviation Electrician (1959-1965) I had to setup what was known as a 'carbon pile regulator' for the 24VDC/ 300A aircraft generators.; such as were used on the S2Fs, P2V, C45s, C54s, C118s, and many others.
With a 2 or 4 engine aircraft supplying 28VDC to one or more common (house) buss it was imperitive that the generators not have any power fed back into them, else they would try to become motors and burnup the field windings and most likely take out to 'supply' generator.
The generator's regulator had to control the DCV field current/voltage through a device much like a volume control. This control element was made up of a group of carbon buttons inside of a tube; thus the term of 'carbon pile regulator'.
What made it possible form multi-generator function was an added electrical part in the the regulator called an 'equalization coil'. This coil sensed the buss voltage and the current supplied from the other generators and 'fine tuned' the the load distribution for each generator.
Normally this setup in buss pairs.
After all these years I am surprised at how much I can recall from the work. I guess this where I start to lose my short term memory and enhance my long term memory. Boy thos efish seemed soooo much bigger now.
Some of todays alternator systems are 'smart enough', along with the reverse diode protection to eliminate what was a serious challenge when we ran generators. Here the demand is that the diode be capable of handling the max current, plus a surge amount, for a safe period of time and temperature.
In the my old days of as an Aviation Electrician (1959-1965) I had to setup what was known as a 'carbon pile regulator' for the 24VDC/ 300A aircraft generators.; such as were used on the S2Fs, P2V, C45s, C54s, C118s, and many others.
With a 2 or 4 engine aircraft supplying 28VDC to one or more common (house) buss it was imperitive that the generators not have any power fed back into them, else they would try to become motors and burnup the field windings and most likely take out to 'supply' generator.
The generator's regulator had to control the DCV field current/voltage through a device much like a volume control. This control element was made up of a group of carbon buttons inside of a tube; thus the term of 'carbon pile regulator'.
What made it possible form multi-generator function was an added electrical part in the the regulator called an 'equalization coil'. This coil sensed the buss voltage and the current supplied from the other generators and 'fine tuned' the the load distribution for each generator.
Normally this setup in buss pairs.
After all these years I am surprised at how much I can recall from the work. I guess this where I start to lose my short term memory and enhance my long term memory. Boy thos efish seemed soooo much bigger now.
Some of todays alternator systems are 'smart enough', along with the reverse diode protection to eliminate what was a serious challenge when we ran generators. Here the demand is that the diode be capable of handling the max current, plus a surge amount, for a safe period of time and temperature.