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hi everyone welcome to another session of boatingtechtalk.com uh we've got a question from a fellow voter and this boater alex asks the following question jeff uh he starts off by saying i've got a sport battery a starboard starboard battery a generator starter battery a house bank and then he goes on to saying i also jeff have a port alternator that charges the house the starboard alternator charges the two starter batteries okay all right that's the setup let's go so he keeps on going and he says uh i may be missing something but how does my generator battery get charged and this is a really good question how does one's generator battery gets charged does the generator charge its own battery what's the recommended setup can you charge three separate batteries okay so this is basically about a question about what charges what specifically when it comes to engines alternators okay the reality is that pretty much every uh not you can't ever generalize and say everything but i haven't seen a generator that doesn't have an alternator so i didn't want to use a blatant statement and say all generators have alternators but pretty much all generators that i've ever seen like pretty much all engines for propulsion have alternators so it's normal for us boaters to assume that an engine and or a generator will have its own alternator now there are differences and the differences are on its output a generator alternator or the alternator on your generator is not really meant to recharge a lot of battery banks or a large battery bank it's meant to recharge the battery that was used to start the generator a little bit like um you know maybe a sailboat engine right that engine has its own alternator and the alternator is generally going to be recharging the battery that started the engine so uh in this situation for alex what we've got is the owner is asking well what's recharging my generator well the whatever started your generator so if you have a battery switch or source selector switch what generally started your generator is also getting a charge now how would one go about confirming that because it's one thing for me to tell you what happens but all of us have got to be curious and so what you're looking here for is you're looking for a change of voltage right so first of all what you should notice is with all your engines off with disconnected from shore power no solar panels connected to your batteries no methanol fuel cell basically you want to remove all charging sources first thing is notice what are your voltages on all of your batteries right you're at rest voltage it should be anywhere because now there's no more chargers anywhere between 12 8 to 13 3 13 4. now at rest battery voltage is certainly not 13 but it takes a little bit of load for that battery voltage to go down below 13 so it's possible for you have disconnected a battery charger and basically call residual voltage to be around 13 2 or 13 3. the moment you apply a large load that voltage or surface voltage will just go down to 12 8 or 12 6. okay so now what you're doing is you're you're measuring the voltage across all your batteries and that's the at-rest battery voltage next is going to be basically and hopefully you've got a volt meter is would would be to turn on your generator and see what happens to that battery voltage as you start the generator you should see that starter generator starter battery voltage go down drastically because why it's starting your generator now it might go down as low as 10 maybe nine and a half might be 11 depending on the size of your generator battery but it's going to go down from whatever it was so the second thing you're looking for is you're looking for a drop in voltage as you're starting the battery or the generator and also remember you're also your generator might have glow plugs so even if you're just turning on your engine your generator you might be able to see you know a drop a little bit drop of voltage as you maybe are engaging glow plugs or however your generator draws power and then the next thing that you're looking for is once the generator starts outputting after about a minute you should see that battery voltage start to increase so it might have been a 12 8 or 13 3 but now that the all the generator is running and that its alternator is running you're gonna now finally see that voltage of the battery that started your generator to start to rise okay so that's the first step figuring out which battery does what and sort of looking at the voltage is a good way to trace and to find out what battery does what on your boat next question or a sub question with an aleks question part two is well how can i charge multiple battery banks with either one single engine and you can do that other than a generator right because as i said the alternator on a generator is small and it's not really meant to be recharging multiple battery banks so we've never installed a battery combiner and or a battery isolator on the output of a generator alternator we have not done that and the reasons for not doing it is because we simply don't believe that a generator alternator in most cases is big enough to handle recharging more than one battery and certainly not recharging a battery that has been discharged in a deep cycle application that needs to be a lot recharged so for your other engines then your choice of sharing that charge is going to be either through a battery isolator and there's a lot of videos and articles on that on our website a battery combiner which is a way for sharing a charging voltage battery to battery or alternatively you could also look from battery to battery doing what's called a dc-dc charging converter all three of those devices on our apps website and we've got huge write-ups and lots of videos that cover each one of them so basically that's the question is what battery starts or runs my generator and how does it get recharged it gets recharged by the alternator and the one that starts the generator is most likely going to be the one that's going to be receiving the generator alternator recharge so great question alex a little confusing but it's a great question thanks for asking if you're curious we've written whole articles about this go on our website search it out and we've got a lot of other tech talks about this very topic if you haven't subscribed to this channel please do um it actually it really does make a difference it encourages to keep posting so if you're watching this video and haven't had a chance to subscribe we really do care because the more of you that are watching the more of us over here are willing to spend more time in creating content so thanks again Videolytics    Tools Videolytics