No start after rewiring alternator 4.3 Mercruiser

[Wakeboarder141]

1990 Bayliner Capri 1850 4.3 Mercruiser

I am rewiring my alternator to swap to my house batteries instead of the starting battery. In the process I have somehow created a no-start situation. It's probably something simple I did wrong, but I am unsure. What I did was remove the main cable going from the alternator to the starter, and relocated that so it goes from the alternator to the house battery. I also removed the red/purple voltage sense wire that was on the slave solenoid, and attached it also to the positive terminal on the house battery. I did not reconnect anything to that stud on the slave solenoid. Now, when I turn the key all I get is the slave solenoid making a single click. If I jumper the slave solenoid with a screwdriver the boat will start. Hopefully someone can help.

EDITED: I had inadvertently forgotten to connect the new ground wire to the house bank, so that fixed my no alternator output, but still just a single click when turning the key.

 

[Chris1956]

I guess I will bite. What are you trying to achieve by rewiring the alternator?

If you want to charge the house batteries, a battery switch is more flexible as it will allow you to charge house battery, starting battery or both.

Normally the starting battery powers the ign switch, thru the large plug on the motor. Perhaps the ign switch doesn't get any power?

 

[Wakeboarder141]

I guess I will bite. What are you trying to achieve by rewiring the alternator?

If you want to charge the house batteries, a battery switch is more flexible as it will allow you to charge house battery, starting battery or both.

Normally the starting battery powers the ign switch, thru the large plug on the motor. Perhaps the ign switch doesn't get any power?

It was suggested by Blue Sea to swap them so the large house bank is charging first, then the ACR will add in the starting battery to the charging. I haven't actually installed the ACR or switch yet. They wanted the larger bank to be directly connected to the alternator. I have full power from the starting battery to the ignition switch. Everything else works, except the solenoid isn't engaging the starter. Am I missing some function that the remote sense wire had when connected to the solenoid? Unless the solenoid happen to go bad during the rewire, I don't know what else it could be.

 

[Wakeboarder141]

UPDATE: As suspected, I had messed it up. I'm still not sure where that sense wire terminated, but it is not on the solenoid. I replaced the wire to the solenoid, and it now cranks again. The alternator is now charging the house bank as intended to be shared via the ACR to the starting battery.

 

[Chris1956]

Good plan (actually stupid plan). Now you can use your fully charged house batteries to listen to the stereo, make drinks etc, at the end of the day while waiting for a tow 'cause the starting battery wasn't charged.

Not sure I agree with Blue Sea on that one.

 

[Wakeboarder141]

Good plan (actually stupid plan). Now you can use your fully charged house batteries to listen to the stereo, make drinks etc, at the end of the day while waiting for a tow 'cause the starting battery wasn't charged.

Not sure I agree with Blue Sea on that one.

Why would the starting battery be dead? The ACR shares the alternator charge with it.

 

[Chris1956]

OK, then why rewire alternator to charge house batteries first? That directive does suggest a priority for charging batteries, and I think it is the wrong one.

If your house batteries get low on charge, but your starting battery is fully charged, at least you can get home.

 

[Wakeboarder141]

OK, then why rewire alternator to charge house batteries first? That directive does suggest a priority for charging batteries, and I think it is the wrong one.

If your house batteries get low on charge, but your starting battery is fully charged, at least you can get home.

Again, just following the recommendation of the ACR manufacturer. I don't know why it is even matters except for the first 2 minutes before the ACR kicks in. The switch does have an emergency combine feature for jump starting if there were ever an emergency.

 

[jhande]

According to Blue Sea's website:
What is an ACR?
An ACR parallels (combines) batteries during charging, and isolates them when charging has stopped and after battery voltage has fallen. An ACR is intended to keep a load from discharging both of the batteries.

I couldn't find a wiring diagram.

 

[Chris1956]

An ACR is likely their version of a battery combiner. A battery combiner is a continuous duty solenoid and some electronics to control the solenoid. The motor will charge one battery until it is full then the solenoid will close combining the batteries for further charging. When charging stops, the solenoid opens.

I still think you want the starting battery charged first, and therefore disagree with the recommendation of Blue Sea.

 

[sam am I]

Either way, when you parallel (ACR comes on/batt switch in "both") a dis-charged battery (house for example) with a charged battery (start for example) the batteries have to "equalize"......

Which means?

The second a charged battery is electrically connected to the discharged battery's (alt running or not), the voltages of both battery's are FORCED to be equal (less any inherent resistance) to one another, this then of course makes stored energy from the highest voltage potential battery (start batt) to DISCHARGE into the lower voltage potential battery(house batt)........

This is not best practice, invest in a system that leaves the charged battery fully charged up and PROTECTED and only charge the battery/s that requires it.........Simple!

 

[Wakeboarder141]

This is not best practice, invest in a system that leaves the charged battery fully charged up and PROTECTED and only charge the battery/s that requires it.........Simple!

Such as? This was my intention, but apparently not my result.

 

[sam am I]

Such as? This was my intention, but apparently not my result.

Few ways.......But in your case since you have an regular alternator (rotor type) that sounds like is being wired with remote sense AND if it were me with that set up, I'd most definitely use a schottky diode type that has remote("compensation") sense.....

Amazon.com

Little back ground.......

The diodes "steer" the current and prevent the battery's from drawing ANY current from each other, charge current is directed ONLY to the alt when it runs.

For example,

The start battery can sit full at 14.3V and the house can be down at say 10.5V, again, the diodes allow this without any current flowing between the two), your start battery is protected/Isolated and remains at 14.3V until you use the ignition/start the engine...........

When the alt fires up from the above example, the alt's output voltage will for sometime sag down to the lowest batt (10.5V in our example)) as charge current flows from the 10.5V battery to the alt HOWEVER, the start batt is still full(less what was just used) and still isolated at 14.2V (12.8V) as it's diode remains reversed biased.....The batteries remain isolated even when charging......BONUS!

The house battery will eventually come/charge up to say 14.3V, but NEVER will the diodes allow the batteries to draw current from one another, hence are never connected together when charging or dis-charging.

Totally solid stated, no moving parts, schottky diodes have a very low Vf and thus stay much cooler then old school Si diodes, and with the remote sense (compensation) hook up, the batteries will always top off at the proper 14.2/14.3V.

The opposite holds true if the start batt is low and house is full......AND when and if both batteries require any amount of differing current, they both get what they need (alt willing) independent of the other.......They draw charge current only from the alt. as needed and NOT each other having to discharge one to only then re-charged it.

 

[Chris1956]

Sam, Diodes like in Battery Isolators always had a voltage drop when charging the secondary battery. Has that been solved?

 

[sam am I]

Sam, Diodes like in Battery Isolators always had a voltage drop when charging the secondary battery. Has that been solved?

"and with the remote sense (compensation) hook up, the batteries will always top off at the proper 14.2/14.3V."

So no, there is still that pesky forward votlage (Vf) **drop HOWEVER there's a work around, yes!!!

When using his/the alt's "sense" wire connected to the iso's *built-in "compensation" terminal, the alt NOW will automatically step up it output voltage to make up (compensate) for the/any Vf drop.

eg, instead of normal 14.3V at the output of the alt, and for example, with a schottky isolator connected and his alt's sense wire hooked up properly to the iso's comp output, his alt's output will be up around 14.3V + **0.2V = 14.5V.

Therefor after the isolator and back at the battery/s + terminal/s, it'll be the standard/proper 14.3V again........It's "compensated", JOY!!!

*Embedding the comp diode internal to the iso additionally compensates for thermal changes, i.e., if and when the diode's PN junction temp rises, so can Vf....Embedding all the diodes together assures the comp diode "tracks" 1 for 1 any Vf differences the iso's battery diodes might be having. This feature then obviously helps keeps the alt's output that much more accurately in step with temp changes that can occur due to differing current loading and/or ambient changes.

**Stardard Si Vf @ 70F is around 0.5/0.6V, Schottky is around 0.1/0.2V min.

 

[jhande]

Silly question, because this is all new to me.
Couldn't one of those 2 battery switches be used?
Something like this:

https://www.amazon.com/Ampper-1-2-Both-Off-Battery-Disconnect-Isolator/dp/B07PN9CT9H/ref=sr_1_3?dchild=1&keywords=boat+2+battery+switch&qid=1621446233&s=automotive&sr=1-3

 

[sam am I]

Silly question, because this is all new to me.
Couldn't one of those 2 battery switches be used?

Well heck NO!! That is just too simple man and there's NO app!!!..............J/K!!

Sure ya can and that's all we had in the "great before" and we're all still here safe and mostly sane, just remember to do some mindful switching from time to time, no biggie.

 

[jhande]

Well heck NO!! That is just too simple man and there's NO app!!!..............J/K!!

Sure ya can and that's all we had in the "great before" and we're all still here safe and mostly sane, just remember to do some mindful switching from time to time, no biggie.

LOL

Thanks!
I was considering using a switch if I ever get to the point of having a second battery and a trolling motor. Just wanted to make sure I was going down the right path.

 

[Chris1956]

Gee, with a battery switch, you don't need no stinkin ACR.

 

[sam am I]

Gee, with a battery switch, you don't need no stinkin ACR.

Nope.........a VSR/ACR is nothing more then a automatic battery switch cept worse IMO. With a battery switch at least you aren't always forced to parallel/"both" your dis-charged house battery with your topped off start battery to re-charge it.

With a switch and only a 40A alt, I just had to do some mindful switching from time to time.....There could be worse things in life eh?

Did it for years and years, left it on "both" only a few times, but as already stated, being mindful, never had left it in "both" for an overnight camp out or the like.