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What Is the SI Post for on an SI-ACR Battery Combiner?

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we've got a question from a fellow boater named Keith uh Keith  goes about and asks the following question he says Jeff I'm going to partially rewire my house and starboard engine battery to separate them good idea right separating house and engine battery always desirable try to keep your checking and your saving accounts separate and not always together uh Keith goes on and says by the way I've got a single on off battery switch for the starboard engine and the port engine so um we'll talk about a little bit about that later uh that's a note but uh we want to make sure I'll bring clarification that and then he Keith goes on to say the starboard engine switch controls the house and the starboard engine battery okay that's not unusual and and my idea is to cut or to install a ACR which is a battery combiner ACR is from Blue Seas between the new deep cycle battery and the starter battery on the starboard engine and then Keith goes on asking with this new uh starter isolated ACR which is uh ACR stands for automatic combiner relay he's wondering what should I do about that si uh post on a battery combiner SI starts for starter isolator all right so Keith I sort of laid out the groundwork groundwork in a way that for all of us as boaters realize that everything seems maybe easier before we start and things get a little bit harder as we go along but that's normal it's about it's to be expected if it was a boat if it isn't a boat it's easy if it is a boat it's not easy uh so first things first uh when many of us as boaters will find that our house and engine uh loads are actually coming onto a single battery it's quite common actually um not everyone agrees or thinks that engine and house loads should be separate that's the first sort of like you've got to recognize that is that it's not a mantra it's an approach and not everyone agrees with the approach of having dedicated engine battery and house batteries sounds like Keith is going in a way and trying to separate his house loads from his engine loads so that's easy to do right having taking some loads off one house battery taking the other lows off the engine battery and that takes some cleanup but the challenge is how do you have a a new battery get a charge either from the alternator or also from a battery charger one easy way to do that is to introduce a battery combiner and a battery combiner from Blue Seas is called an ACR which stands for automatic combiner relay okay all right so we've got these battery combiners and the reason why people choose to install them on boats is a way for paralleling Batteries whenever there's a charging voltage and that charging voltage could be triggered by solar panels could be triggered by an alternator could be triggered by an inverter charger I.E the charger function of an inverter charger it really doesn't matter and these battery combiners have a tiny little post on them and one of that posts is called an SI which means starter isolator and that is a way for you to basically make sure that even when there's a charging voltage um and I.E the combiner is engaged and the batteries are parallel that before you when you start your engine that your batteries are separate I.E that your house and engine battery which are normally combined through this ACR won't be combined when you start your engine now the question might be well why would I care Jeff well there are reasons for doing that albeit very few people would go down that road I think it's an interesting feature that is rarely implemented because it's it's a little harder than it sounds um but it's doable and it's a way to make sure that whenever you actually crank your engine and let's say for example a battery charger is on or solar is energized and your battery combiner is actually engaged and your house and engine battery are parallel when you start that engine you're actually going to only be starting the engine not off the house and engine but only through the engine battery and so it's a way to make sure that you also don't have voltage uh I guess drop significant voltage drop under starting because let's for example if your electronics you've got a bone in your chart plotter Sounder is wired to your house battery and suddenly your battery combiner is engaged because it senses somewhere that there's a charging voltage on either battery when you go to start your engine the house battery is going to help to if the battery combiner is engaged well what's going to happen to the house battery the house battery might go down to 10 volts 10.5 volts which is not unusual for a starter to cause that to a battery but then what happens is your electronics that are running off your house load might be susceptible to a low voltage disconnect right so if the battery voltage goes below or what they Sense on their chart plotter goes below 10 volts well you might actually trigger a reboot and so the SI post is a one way to avoid these hassles and the SI post another feature of why some people would choose to implement it is that it allows you to know before you leave the dock that only your engine battery is good enough for you to start the engine and so you don't want to have all your eggs in one basket when you start your engine especially at the dock that's the time where you want to know can I actually start my engine with only my engine battery nothing wrong with having more batteries to help but you don't want to go as your first step have all your eggs come into play meaning that you have your house and engine battery starting your engine because what if you need help when you leave the dock right and you only have your engine battery well then it's going to be worse than what you did at the dock which is having house and engine so that's the reason why some folks choose to install a choose to utilize the starter isolator post SI post on a battery combiner which by Blue Seas is called an ACR which stands for automatic combiner really so a needy little greedy question from Keith but thanks for asking and thanks for all of you for tuning in much appreciated 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

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