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hi everyone I'm Jeff Cote here with boating techtalk.com uh we've got a question from a fellow Builder asking about some issues with a batter isolator so this Boulder sets up the stage so in this instance we've got a boulder that has two battery Banks a starter battery bank and an Electronics battery bank and that battery bank is charged from an alternator via a battery isolator now with this voter notice is that when his engine is running they don't really notice that much current or recharging happening on their Electronics bank and remember the electronics bank is recharging via a battery isolator so the first thing to realize is that not all battery isolators are the same so some battery isolators are efficient and some of them are inefficient and what you're looking for is are they modern with fats or are they made with diodes older battery isolators have and you can tell them apart from the newer ones because they have basically a heat sink on it because diodes allow current to only go One Direction which is what you want with a battery isolator you don't want the electronics battery or the engine battery to see one another but you want the alternator to be able to recharge both so in order to have two things connected together but separate you either do it through a battery isolator that is with diodes or you do it with the battery isolators that it fets now the challenge with the older style battery isolator the diode one is that it would actually cause a about 0.7 voltage drop and you're thinking oh 0.7 not a big deal I got 12 volts what's 0.7 on 12 well the reality is that when you're charging a battery your max voltage if it's a 12 volt battery is around 14 4 maybe 14 6 and that's at Max output of the alternator if you're taking that and you're at 14 4 and you do -7 so now you're at you maybe 13 7 instead of 14 4 and that's 13 7 without line loss so you know you're obviously your alternator is not on top of the battery and depending on the size of the wiring and you might be losing 0.1.2.3.4 volts of line loss between the alternator and the electronics battery bank and so all of that is aggravating things it's just making it worse right you've got your alternator output you're losing 0.7 out of that then you're losing 0.2.3.4 out of line loss so effectively you're trying to recharge your battery at 13 4 maybe 13.5 well what are your loads on your electronics Bank some electronic banks are five apps seven apps 10 apps and if your alternator is only a 55 amp stock alternator a 35 amp alternator and you're running that through a battery isolator who's chopping off 0.7 volts just to provide that feature right on top of line loss you're going to have a device that effectively can barely recharge your electronics battery bank and that happens all too common so the first thing that you should consider if you've got this setup or challenge is to replace your older type battery isolator with a modern fat based uh battery isolators because those battery isolators are way more efficient you might lose five percent but you're not going to lose 0.7 volts and so that's one of the common things we do when we come on board and we're doing electrical Audits and if we see a older type battery isolator we're going to recommend to the owner to consider replacing it with a modern fet type a battery isolator where most of all the power coming out of the alternator is redirected to the battery Banks and is not lost um in the device itself hence why they have this huge heatsink so consider that and then also think about when we're idling right or we're having our alternator at lower RPM output so depending also if it's a gas or diesel but where you're not all alternators output the same amount regardless of your RPM generally there is a correlation between RPM which affects the rotation of your engine but also affects the rotation of your alternator obviously with the pulley ratio being different but it still affects your output so if you're idling and you've got a diesel engine and you're idling around 1200 1300 1400 RPM while you're maybe trolling or going slower your alternator output might not at all be what you expected even if you have a stock 50 amp alternator when you're trolling at those speeds and your engine is rotating at only 1200 you're going to see only a fraction of that output and so it's sort of like almost these layers where every time someone is you start off thinking you've got a 50 amp alternator but now you've got 50 amp running at maybe low output so maybe instead of running Max 50 it's only outputting 20. oh but now it's 20 amp output because you're going slow and then you're like oh I'm going to run it through a battery isolator well the battery isolator might take another like two-thirds of that power so now my engine my electronics battery is only seeing like 5 to 10 amps charging oh wait I've got loads on my electronics I got sharp blotter I got a Sounder I've got maybe a stereo I've got maybe a radar maybe I have an AIS all those loads I've got a crab puller or pot puller or whatever it is and now all those loads are actually going to exceed the charging capacity of your alternator on your boat so one way to do that is to replace that uh battery isolator which is inefficient and realistically the other reality and some of us have this is that sometimes we want to run our engines slow for a long period of time but we can't because we're just not making enough power so be cognizant and have a battery monitor on your electronics bank and say wait a second the voltage I'm going in a negative over time now I can do go in the negative for maybe two hours maybe four hours but maybe I won't be able to do it for seven or eight hours and then it does happen I hear it all the time you know I'm running my engine and my engine my batteries died when the engine was running is my alternator damage well it depends and that's the question is your alternator output exceeding all the loads on your boat at any given time and that's not always the case so a great question from a fellow Boulder and as we can tell everything appears easy at the outset but sometimes it's more of the devils are in the details thanks for watching and if you've got any feedback or input on a battery isolator on your boat please share because remember sharing is caring thanks for watching so if you're curious again go on our website and find out more answers and solutions with this sort of setup and thanks for asking and thanks for all of you for listening and tuning in