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hi youtubers jeff cote here with  pacific outsystems we've got a question  from frank  frank asks jeff i've been watching your  videos about fusing the alternator and  you recommend always carrying a spare  alternator on board  how do you tell when your alternator has  blown oh  lovely question by the way most of us  unfortunately and this is bad assume  that things work on our boat  and the reality is uh assuming that  things work on our boat is probably  gonna  get us into hot water or trouble so how  does one tell if your alternator is  working  i love that question uh so first thing  is  an alternator is not this thing that is  either on or off that you can just  tell it's not that easy it's all about a  change and think about a little bit  a pool of water uh your alternator is  sort of like um  it's a pipe feeling a pool of water and  your pool is your battery  so what happens is you always want to  see and this is this is how you do this  you  you basically look at the voltage at  your battery prior to starting  your engine so what is your battery  voltage it might be 12.5  it might be 13 volts it might be 12  volts but you want to know what your  battery voltage is  on your engine battery prior to starting  your engine  when you're going to actually activate  your starter obviously the voltage will  drop  it's going to drop because there's a  large load your starter is drawing a lot  of amperage  so you might draw to 11 volts 10 volts  nine and a half volts  you're going to see a big drop in  voltage but here's the key  and this is the key once your engine has  started and give it about 30 seconds to  one minute and also make sure that  you're revving on the rpm so some  alternators no output at 800 rpm so you  need to be revved up around 1100 rpm  but at this point you should see an  increase of voltage from where you  started  so if you started at maybe 12.5 volts  and if your alt if your voltage on your  battery when your engine is running is  12.3 that means your alternator is  not working because what you should have  seen is a positive  outcome something the voltage should be  rising and if it's not rising  why not that's because your alternator  has failed  so your alternator should be rising the  battery voltage  so if you start and your battery voltage  was at 12.5 and now that the engine is  running  maybe your battery voltage will go up to  13 1 13 3  13 4. or if your alternator is properly  sized and it's a pretty big alternator  and your battery bank's not all that big  like in our cars for example in our cars  our car batteries not that big our  alternators are pretty significantly  they're they're huge compared to the car  battery size  instantly the battery voltage is going  to go to 14 4. but on a boat because our  battery banks are  really big and our alternators are not  all that big it might take time to get  to 14.4 volts  which is the target voltage of an  alternator so what you're looking for is  seeing an  increase in voltage when your engine  starts  and that's how you know if your  alternator is working  thanks for watching