Removing the evil port/starboard selector switch - dual ACRs

[BlueDefender]

The main electrical panel door has that big Kraus & Naimer electrical switch for selecting which engine (port/starboard) will charge the house battery.

That switch, IMHO is a weak link in the electrical system of the boat. The switch is the only electrical component that does not have crimped-on ring terminals for it’s connection and instead has a screw-down connector on bare wire.

For a long time, I chased an electrical issue where my house battery would sporadically drain to a very low voltage (10.8v) even while the boat was running. I’d probe things with a multi-meter and things would seem to be working again with the alternator kicking out 14v like normal. It took me a while to figure out, but what happened is the screw terminals had backed off and gotten loose. Rough seas or hitting a ferry wake hard would move things around enough such that the alternator connection dropped to the battery. When I opened the door panel to ‘investigate’ the motion of the door wiggled the wire enough that it started working again.

If you don’t attempt this upgrade, then you should make sure to regularly check the screws are cranked down and tight on your K&N switch terminals.

The wiring for the batteries looks like this:

After poking around on BlueSeas website learning about the ACR (Automatic Charging Relay) and talking with a very helpful Safeboat electrician - I realized that the ‘modern’ way to charge a house battery with two outboards is to use two ACR (automatic charging relays) rather than a selector and a single ACR.

So my goal was to move to wiring that looked like this:

In this configuration each engine feeds it’s own ACR which combine output to charge the house battery.

This is the before-shot of the panel:

and behind the panel door you can see all the positive wires routing through the switch.

If you look inside you can see where the single ACR sits. There is plenty of room next to it for a the second ACR, but the battery vent hose in my case had an awkward 90 connector on it - so I changed this out to a straight connector to get more space.

You’ll also notice that in addition to the positive cables, there is a ground connection on each ACR to allow it to show status on the LED lights.

Here you can see the after-shot of both ACRs installed

In my case, I took the output of each ACR and ran each one to the positive house battery terminal. The downside of this is you end up with 3 lugs stacked on the house terminal vs. two before, but this is well within ABYCs limit of four connections on a stud. Apparently the way Safeboat wires these is they connect the two ACRs directly with a short piece of bus-bar and then run a single cable to the house battery. I opted for two wires as I had plenty on hand and no bus-bar.

To mount the 2nd ACR requires drilling into the aluminum and installing nut/locking washers. You can also see in this final shot the straight connector for the battery vent hose making more space.

The final step of the project was to pull the door off, patch up the holes and repaint it.

Looks cleaner and I sure don’t miss having to to mess with flipping that switch before each outing.

Manuals and specs on the SI-ACR can be found here:

https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

Things I needed for this project:

• 25ft spool of 2 AWG Red
• Blue Sea 7610 SI-ACR
• 2 AWG 3/8" cable lugs
• 16 AWG ground connection wires and crimp terminals (already had)

One final note, if you’ve ever looked at the back of the panel door, you may have noticed that the nuts holding the switches in place have little tails of heatshrink tube on them, you may have some that have fallen off over the years. I asked the Safeboat electrician why they did this vs. just liquid electrical tape, and apparently they are more for abrasion protection than they are insulation. Someday I’ll replace my missing ones, but its low on the list

[05rbs]

Wondering if anyone removed the ACRs all together? I don’t love ACRs, especially when each battery has a different use.
I’m thinking about using two Victron DC to DC chargers instead, they will give me the ability to have true charger profiles and eliminate the need for the ACRs / Selector switch.

Thoughts?

[BlueDefender]

curious what you don’t like about ACRs… ?

[05rbs]

Two issues, first and most importantly they will make the battery look as one, meaning you can’t use any sort of charge controller (I might be unaware of hacks to this), so if your house is at 12.2v and start at 12.7 it’s going to treat them as one combined battery.
Second is other sources will activate them, example is an AC charger on your start batteries will engage the relay, if you try and start the engines before disconnecting it will draw from both, a strong enough solar setup will do that too….

[BlueDefender]

What’s the downside? Combining when on charge would just eventually top up both house and starter right? Or are you wanting to prioritize where the charge goes given a limited amount of time to get charged?

I guess in a solar situation it would mean that a temporary burst in solar causes a combine, which steals from the starter to top up the house and then the solar flow drops - so you effectively lost voltage from your starter? Seems like an edge case though - in that case just combine the starters - fire the motors and go drive the boat and let it all get fixed up by alternator

[05rbs]

For the combined battery scenario on charge you will decrease the life of the batteries by not following a charge profile, alternators are not nice to batteries which is one reason start batteries don’t last that long and why larger systems have charge controllers.

On the solar or AC charger route you are going to draw from your house battery too on start, many electronics are cool with a drop but it can also introduce surges, that was the original reason behind the ACR (as I understand it).

A balmar 614 costs 300 plus bucks, I guess the core question is why not do dc/dc chargers, in the big boat case it’s cost as the 614 provides charging profiles for 300 and it’s way less than 7 30a dc/dc chargers (which would look silly)… but on the safe a dc/dc seems interesting

[05rbs]

Assuming a 200a aux alternator and 30a Victron chargers on the 7 dc/dc chargers

[Theleafblowerguy]

Anyone tried out new li-ion 12V batteries? Have a neighbor that just put a small one on his dingy and apparently loves it.

[BlueDefender]

I believe @05rbs (he’s just around the corner from you) has them on his tug and has considered them on the rbs but not done it yet.

I haven’t looked into doing a swap to deeply yet - but my limited understanding is that it’s not a simple direct battery swap. I believe the problem is that lithium batteries can suck down a lot more power from the alternator than it was rated for - and you can end up burning out the alternator on the outboards. I assume some kind of regulator/charge controller would fix it (vs rely on the BMS on the battery).I’d definitely consult with a marine electrician before doing it - or maybe someone else here has some experience already.

Pacific Yacht Systems has some great YT videos on similar topics you might be able to find the answer from.

Sure would be nice to drop all that weight in half and have the hull lean back to starboard a little more

Oh - also - most people are using LiFePO4 now vs Li-Ion as it’s more stable and less prone to spontaneous fires.

[05rbs]

Yep I have LiPo on the trawler for the pilothouse systems, still using lifeline AGMs for the inverter bank. Overall they are much better and the price is fairly reasonable versus AGMs which have gone up a lot. As mentioned it’s not an easy swap, you need to have some sort of LiPo compatible charging setup, and even then make sure it’s dialed in. I went with all Victron on the trawler, will swap the inverter bank after the summer trip but will also want to swap my inverter out and likely need to flash or replace my balmar regulator.
I haven’t looked at what this would take for the RBS, I’m very happy with my new blue tops and combo of Victron AC charger plus 200w of Solar with a Victron controller.

I wouldn’t touch lithium ion on a boat, I also believe insurance might be an issue, too many fire stories.