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

Keith has a Tiara 2900, and he wrote to ask, "I am going to partially rewire my house and starboard engine battery to separate them. I have a single on-off battery switch for the starboard engine and for the port engine. The Starboard engine switch controls the house and the starboard engine battery.
My idea is to cut in an SI-ACR between the new deep cycle battery and the starter battery on the starboard engine. With the SI-ACR there is also a center stud for starting isolation. Can you help me with the use of that stud if it is needed in this case?"
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[@thecastman12]

Glad you’re back! I have an ACR-SI, installed by a previous owner. The SI connection was not wired in. So, I wired it in. Only after a little trip to the San Juan’s did I realize I wired to the wrong post on my starter switch. The “run” post. After repeated startings, one morning at anchor it wouldn’t start. I jury rigged my solar panels to my starter battery for a couple of hours to get started. I also disconnected that SI wire. I had effectively taken my starter battery out of the charging circuit. Who knew? My previous trips had been short enough that I was always back at the dock on shore power.

[@PacificYachtSystems]

it needs to go onto the "start" wire which only has power while the motor is cranking. It will be the small wire on the starter.

[@NotMitch69]

Love it. Yeah, the SI-ACR is for people who want to charge both house and starter banks with the same charging source(s), but ensure that only the starter bank does the starting. You attach that post to your starter and when the ACR detects the surge to the starter, it disconnects the combiner.

[@mohamedalmuhairi324]

Welcome back and thank you for the great info

[@RBibberJr]

Thanks for the info I was wondering about that? HOW would I wire the SI post? Does it run to a manual switch? Ignition? Is SI automatic during starting? Still a lot of unanswered questions...

[@2010willyz]

Very good timing on this content. I am in the process of purchasing a boat with bow and stern thrusters. When using the rear thruster the electronics are affected by voltage drop. I was planning to add a dedicated battery for the rear thruster (front already has one near bow) but I think to make things simpler I will just run it off the start battery but use a combiner and utilize the si function to isolate the draw from the house batteries whenever the thruster is engaged, therfore keeping voltage drops away from electronics.

[@PacificYachtSystems]

I have used the Si function to a bow thruster control. It works well. can be tricky to hook up to the thruster.

[@jorgeangeleri9516]

Long time no see! Welcome back!

[@donlindell1994]

Charge voltage to engine battery should go through lead-acid charge controller as well. This would also limit the V-A impact to the house circuit. Either way, this video was very insightful.

[@fratermus5502]

1:15 and elsewhere: "automatic combiner relay" - Blue Sea's website and supporting documents say "Automatic *Charging* Relay". Perhaps the nomenclature used to be *combiner* and they changed it? I enjoy your vids even though I don't own a boat!

[@PacificYachtSystems]

Probably just a mistake on my part. This product and it's competitors (vsr etc) are all considered battery combiners. As opposed to a battery isolator which is totally different.

[@rossevans1774]

@@PacificYachtSystems ACR's do not combine batteries.

[@mickmouse92]

Without any other charging sources, would a regular ACR without start isolation ever be connecting both batteries? 13.3 is the cut in. I can't imagine my batteries would be connected until after the motor starts.

[@Beachnative42]

It says on the label ACR - Automatic Charging Replay , not automatic combining relay.

[@rossevans1774]

Yes, and people still refer to it as 'automatic combining relay'.

[@ΕυαγγελοςΚολαιτης-θ2ω]

By using an acr do you need to have same capacity batterys?

[@BYENZER]

JEFF, I agree with all the "reasons" you stated. But, you didn't mention the most important reason. The #1 reason to use the S.I. is to avoid "recoil/fly-back/surge" voltage spike upon starter dis-engagement. During cranking, if the ACR is still combined, and the engine battery is weak, when the starter is DISengaged, the "system" voltage will momentarily JUMP WAY UP. A voltage "spike", if you will. House electronics can be damaged from the spike. The house battery does act as a buffer, but, not if the spike is too high. An o-scope can capture a picture of the spike for your viewing pleasure!

[@PacificYachtSystems]

I am aware of this but I have never measured it. Our avg house bank size is 800ah and I imagine it could buffer a fair bit. On a single house battery It might be more concerning. It would be interesting to measure the spike on different size banks. Many boats are still using a 1-2-all switch and the electronics are always connected to the engine when starting even with no acr. If that spike was really an issue I think we'd see a lot more issues.

[@BYENZER]

@@PacificYachtSystems Yes, most electronics do have power input over-load/high voltage spike input surge "clippers" to self-protect themselves. But, those clippers aren't designed to overcome bad power system designs. They valiantly absorb LOTS of Bad Ju Ju from power system voltage variables. They are the unsung heroes! Sentries, always at the ready. But, they are tiny and can only do so much before being over-run. I hope you do a video, with o-scope captures, revealing the hidden truth on what really happens, when stuff is both turned ON and then, OFF. (Most often, it's the OFF which causes the damage). Most people will be glad if you are more right than I am. Please do put my words to task, on multiple boats. Everybody will benefit, no matter the results. In my work, I have one MANTRA: "Remember to TEST! Don't guess!" For if not, sooner or later, yee will be, forever moored in, the Bay of Regret!" Thank you all, for all you do. The electrical industry needs guys like you. Brett Yenzer Sacramento, California

[@esquire9445]

You look good Jeff… like you lost weight or something. Keep up whatever you are doing you look healthy.

[@choimdachoim9491]

The way I view it is that if both battery systems are always joined, House-use can drain the Starter battery. If the House goes low, not a problem, just an inconvenience. The other way around, big problem...git yer oars out.

[@johnc.wunscheljr2873]

why do I have power to the ground wire coming from the si-acr ?? if you pull the 5amp fuzz and test the fuzz holder one side has +power showing but when you put the 5amp fuzz back it shows no power at the fuzz going to ground?? I'm looking for the reason my batt are going dead with the main switch is off. Any ideas??? please

[@romeofoxtrot2633]

It's Automatic CHARGING Relay. It combines the batteries but only when one can charge.

[@EricEversonArtAndDesign]

So the SI post would be connected to the starter positive to feed a voltage when the starter's engaged?

[@glenn4946]

Connect to start lead on ignition switch. Suppose you could instead tap into same wire downstream where it’s the + trigger for starter solenoid.

[@PacificYachtSystems]

you would need to wire into the "start" wire. It will only have power when the key is being held to start and the motor is cranking. So the acr is only off for a few seconds. if you wired to the positive post on the starter, the SI would be constantly powered and the ACR would never engage

[@kazz003]

Isn’t it very dangerous not to have the SI post wired ? An ACR just used for charging typically has a smaller gauge wire (suitable for charging but not for starting current). Since the only connection to the house battery would be via the ACR, wouldn’t the draw from the house bank (via the lower gauge charging wire) risk a fire ? This is assuming the ACR is engaged. Or it doesn’t work that way :) ?

[@PacificYachtSystems]

I normally wire acr's with 2awg. Both ends are fused at 150-200a. Most of the current is still going to come from the start battery. If too much starting current came from the house battery the fuses would blow so it's not a safety issue. however that becomes a reliability / usage issue because you can't be having those fuses blowing and losing the acr function. But rarely if ever do they blow. I've actually used the SI port for bow thruster banks to disable charging when the bow thruster is in use. as then picking acr wire size and fuses to the bow battery becomes easier. otherwise the acr current can be larger and longer to a bow battery then it would be to an engine battery while starting. But for engines I've never needed the SI port

[@chiphill4856]

Wait, sorry to be confused, but when the start key is turned, does it disconnect the house battery and only use the start battery? Do the electronics cut off and cycle power?

[@coztod]

No, it would separate the house and starter circuits because that what it sits between. It doesn’t sit between the house battery and the electronics and house loads, so it can’t disconnect them.

[@stormer6364]

Hi Jeff, thanks for the video, I have a question. the boat I'm looking at for a friend has agm house batteries and a calcium start battery. My question is can an acr be used with these 2 different chemistries. My only concern really is the disconnect voltage the agms full sit at 13.1v. The acr disconnect voltage is 12.8v so I'm thinking overnight the calcium battery will pull those agms down until it disconnects at 12.8v. Is this a big concern or am o worried about nothing. Regards Stormer

[@PacificYachtSystems]

With a bit of load the acr would probably disconnect after 15 mins or so. An AGM battery is not going to hold 13.1 volts for long with any load on it.

[@stormer6364]

@@PacificYachtSystems thanks for the reply Jeff much appreciated. The only load on it is a rule bilge pump the new gen one that spins every once in a while to check for load maybe the led anchor light too so the loads are very low, the start battery while the acr is connected would be a load tho, guessing fully charged it'd still pull an amp or so from the until the acr disconnects it's 4x100ah powerlyte agms. I was thinking maybe I could put a diode on the negative wire of the acr, am I off the mark here, would that possibly work? Would that lift both setpoints by 0.6v... I could do a bench test I guess before I install.

[@JouniKyyronen-nv1ep]

boils starter battery

[@victore9390]

ｐｒｏｍｏｓｍ ☺️