Electrickery – Wiring question.

[moresparks]

Hi – looking for help on the electrical installation on a twin engine AQ171c’s.
The starboard engine is supposed to have a dedicated starting battery only, but the alternator charging wire is completely missing. It does charge via the b+ which is connected to the starter motor main Positive supply. Is this acceptable?
The Port Engine has a couple of batteries one for starting and the other is the “house” battery.
This isn’t charging as the brushes have broken. I have ordered a replacement voltage regulator so not really a problem.
However all connections on the Alternator are via the B+. According to the manual the Charging sensing wire should be connected onto the D+ which then goes to the Instrument panel via a resistor then feed to other circuits including the renix electronic ignition.
A couple of questions if I may.
If the alternator is not charging will this affect the electronic ignition straight away – The unit has 12volts but I wanted to balance the carburettors and I wondered if I was wasting my time until the alternator is fixed.
I am getting spurious tacho readings on the starboard engine, would this be related or should I look for poor connections? I have checked and tightened everything up including all the earth’s etc as far as I can tell.
Finally – Has anybody improved the wiring / charging with modern digital universal smart regulators or Voltage Sensing Relays and was it worth it?
Thank you in anticipation.

 

[RicardoMarine]

The starboard engine is supposed to have a dedicated starting battery only,
Look over your boat's 12 VDC system. I think that you'll see your house loads being derived from the Stbd engine side. If so, you'll want not only a cranking battery, but also your HLBB (house load battery bank) on this side.
If the Port side does indeed provide house load power... then we'll go with that.

but the alternator charging wire is completely missing. It does charge via the b+ which is connected to the starter motor main Positive supply. Is this acceptable?
Yes.... via the engine harness, this directs the Alternator Charge to the "Common" cable that is directly connected to the starter motor solenoid terminal. From there, it takes the charge to the MBSS "common" terminal, and then to the battery bank that is selected at the time.
This is when manually managing your battery banks!

The Port Engine has a couple of batteries one for starting and the other is the “house” battery.
Are you certain?
Typically the Starboard side is common with house loads.... but this depends on the boat builder.

However all connections on the Alternator are via the B+. According to the manual the Charging sensing wire should be connected onto the D+ which then goes to the Instrument panel via a resistor then feed to other circuits including the renix electronic ignition.
I'd need further explanation on this one. I'm not familiar with a "renix electronic ignition"!!!!

A couple of questions if I may.
If the alternator is not charging will this affect the electronic ignition straight away – The unit has 12volts but I wanted to balance the carburettors and I wondered if I was wasting my time until the alternator is fixed.
It may if the battery voltage is not up to snuff.

I am getting spurious tacho readings on the starboard engine, would this be related or should I look for poor connections?
The Volvo Penta AQ series uses a engine harness/hull harness connector fitting. This white fitting is in the harness, and will be covered with a black double boot affair.
All engine data circuits, including the ignition and helm power Pos/Neg are in this harness and connector.
Pull the connector apart, and examine the contacts.


I have checked and tightened everything up including all the earth’s etc as far as I can tell.
No Earth Ground in a 12 Volt DC system... only Positive and Negative sides.

Finally – Has anybody improved the wiring / charging with modern digital universal smart regulators or Voltage Sensing Relays and was it worth it?
Yes, and there are many components available to help us do this.... (see images below).

Questions:

Does each engine's 12 volt system have an MBSS (main battery selector switch.... Off/#1/All/#2) or a BS (battery switch... On/Off only)?
Does the Stbd engine side battery system also power your House Loads? (many do)

There are several ways that this can be configured.

A..... Port engine has it's own dedicated cranking battery on a BS only.... or it can be an MBSS.
Starboard engine also has a dedicated cranking battery on #1 of an MBSS, and the HLBB (house load batt bank) will be on #2 of the MBSS.
If the Port side uses an MBSS, you can use terminal #2 to join Stbd side MBSS terminal #1 for ALL/BOTH use for emergency "combining".

B..... Port engine has it's own dedicated cranking battery on a BS only, but uses an ACR or VSR to share alternator charging for the HLBB.
Starboard engine cranks on a large HLBB of 6 volt Deep Cycle batteries (two each in series) with the Bluesea 7622 ACR between it and the Port cranking battery. This will offer you more Amp Hours for house loads.... and we can crank on a large bank of Deep Cycle batteries with no issues. (I've been doing this for years now)

In scenario A, you'll need to manage your Stbd cranking and HLBB when on the hook.
In scenario B, the 7622 ACR will manage this for you.


Each engine's alternator will provide battery charging via the engine harness to the MBSS "common" cable, and then on to the battery bank. IMO.... there's no need to circumvent this..... it would just further complicate your system.

If an ACR or VSR is used, the Port engine alternator will contribute to the Stbd side battery bank(s)..... either the cranking bank or the HLBB, depending on which bank is being selected at the time.

Be sure to run a separate heavy Negative cable between engine blocks as to make each engine "System Negative Common".


BTW, most cranking batteries will recieve an adequate charge during engine warm-up. The HLBB is typically the concern.

First image is an example of twin engines with the Stbd side using the HLBB for cranking and House Loads.
This image also shows 2 combined cranking batteries on the Port side.... however, 1 cranking battery is adequate, IMO.

The second image shows two other examples.

 

[moresparks]

Many thanks for your excellent response as always – very muchappreciated.
I only have battery switches unfortunately not MBSS. Allbatteries are 12volt. Wiring must be original 25 years old and overdue forreplacement and upgrading. I am keen to keep the integrity of having onebattery dedicated to engine starting on one engine as on the Instrument panelthere is a battery change-over switch via a solenoid in an emergency. This onlyworks if both alternators are working and you keep the revs at 2000 to switchover.
The starboard engine battery does not power anything else.I suppose I am answering my own questions but I liked the idea of the ACR,s butwasn’t sure if it was worth the trouble and expense as opposed to keepingthings simple.
Probably now a winter project and a bit more studying.
Once again – many thanks.

 

[RicardoMarine]

..........

Many thanks for your excellent response as always – very muchappreciated.
You are welcome. Hope it was useful.

I only have battery switches unfortunately not MBSS.
Either way, I'd keep these from within the engine bay and place them where they are easily accessible without the need to open a hatch.


All batteries are 12volt.
That's OK... unless you use the very large 12 volt batts, you'll have more usable Amp Hours with 6 Volt Deep Cycle batteries for your HLBB.

I am keen to keep the integrity of having one battery dedicated to engine starting
That too is OK.
It's just not necessary with today's ACR's and Auto-combining equipment.

on one engine as on the Instrument panel there is a battery change-over switch via a solenoid in an emergency. This onlyworks if both alternators are working and you keep the revs at 2000 to switchover.
That must be for charging... and not necessarily pertaining to the 12 volt power supply.
Sounds like it may be an old system.

The starboard engine battery does not power anything else.
OK... that is different from how many are set up.
Either way.... you do have one side that powers not only THAT particular helm, but also your House Loads.

My unsolicited suggestion would be..... if you add power for Electronics, etc, that you bring a fresh Pos/Neg circuits forward for these items, and keep them from using the OEM harness for power.

I suppose I am answering my own questions but I liked the idea of the ACR,s but wasn’t sure if it was worth the trouble and expense as opposed to keepingthings simple.
ACR's are simple and are very useful.
IMO, these are very well worth the expense and your time to install.... especially the 500 amp 7622 ML ACR.

Probably now a winter project and a bit more studying.
Once again – many thanks.