Your situation is not all that unique or unusual. Starter Motors can consume heavy amp loads, reducing voltage, as is the case with your electronics. The electronics shut down to protect themselves.
Most twin engine boats, in this size range, supply house loads via the Stdb side engine battery bank. I hate to see you take your House Bank completely out of the loop (isolating it from Stdb engine), but it would resolve your issue, as long as you brought engine alternator charging abililty back into the system..... of which is pretty easy to do!
You would then crank your Stdb engine from your "shared" Port side cranking bank. This too is not all that uncommon!
I'll also suggest that the HTGR/PMGR starter motors require slightly less amps to crank the same engine. These will also usually kick butt over the Non-GR OEM starter motors (if that's what you now have).
IOW, if it's time for a starter motor replacement..... this would be the route to go.... IMO.
These generally cost less as well.
You may want to look at some of the Bluesea products. Bluesea offers some auto-combining switches that may be better suited to solve this issue for you.
If you do separate the House Bank out, consider an ACR (auto charge relay) or VSR (volt sensing relay) that could become integral with your charging system. This would solve your engine alternator charge issue.
BTW, both alternators can charge the House Bank when these are used. There are no inherent issues or conflicts when doing so.
I see that you're using two 6v Golf Cart batteries in series (a group of 2) increasing your Amp Hour capacity...... wise move!
Have you considered adding 2 more? (4 of them?)
I crank my Stdb engine on my large 6v house bank.
While we should NOT crank on Deep Cycle batteries, there are No issues if the bank is large enough! However, I am using the HTGR/PMGR starters. Makes a slight difference, IMO.
Just a thought on that!
The mystery solenoid (with the orange leads) may be an older ACR, or a version of an ACR, that has been added. Hard to tell without more info/detail.
BTW, you could achieve the same "
manual combining" by eliminating your ON/OFF switches, and installing two (2) MBSS's (main battery selector switch) also eliminating your one on/off manual combining switch.
You'd have a total of two (2) MBSS's only!
Your "manual" combing would now be achieved via the BOTH/ALL feature of each MBSS. (i.e., both switched to ALL). However, this requires that we remember to return them from this position!
Bluesea also provides excellent switching components that provide this capability. However, I prefer the
KIS/ALC......
keep it simple and less costly.... and via parts that are easily available.
One more thought that is simple, yet effective.... is a helm switch activated continuous duty solenoid that momentarily combines Port/Stbd banks for heavy cranking loads! (this may also be your mystery device)
I've done this on my own twin engine boat.....
it's my poor man's version of an auto-combining feature.
With a flick of a momentary on/off helm switch at the helm....., the continuous duty solenoid momentarily combines both battery banks (via the "common" terminals) during starting.
I can reserve this feature for a low battery bank scenario....... or to prevent electronics from shutting down.
Either way..... it is simple and works very well.
There is a Bluesea product that does essentially the same thing, but is tied in with your starter motor circuit. More fully automatic, so to speak!
One last note.... I'm a NAZI when it comes to keeping battery cables
ONLY connected to our batteries.
POS/NEG Batt cables ONLY!
Any Accessory circuits can be supplied via the rear "common", #1 or #2 terminals of our MBSS's.
#1 and/or #2 become schematically the same as though they are direct battery connections, but eliminate the typical "Rat's Nest" that we all too often see at Marine Battery Banks...... avoids small terminal corrosion as well.
#1 and #2 will be "Un-Interruptible" (charger leads, bilge pump float switch, radio pre-set memory, etc).
The Common terminal will be "Interruptible" (anything that we want OFF when the boat is unattended... such as our Nav Electronics).
All else will likely be a part of our OEM hull harness (cabin lights, frig, helm power, Nav lights, and so on).
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The Blueseas is good stuff.
The old black bodied Cole Hersee is good stuff as well (fully serviceable too).
Guess is OK.
Perko is low on my list of MBSS's.
I've cut all of the above open to look at the construction.
Again.... just a thought on that!
I'd post some schematics, but you have not asked for any. I don't want to confuse the issue any more than this can already be.
Good luck with this.
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