ACR with two alternators, two banks

My situation.
I have 2 engines, so 2 alternators.
I have 3 batteries, one battery is for starting both engines. 2 batteries for house loads.
I have two 3 way switches, so can combine all 3 or isolate all 3 batteries.

Problem is this.
Anchor out for hours. No problem starting engines.
But the house batteries are low, so the starboard engine alternator gets a hefty load like 60 amps to charge depleted house batteries while port engine alternator is loafing charging fully charged starter battery.

It works but sometimes I will manually combine the banks together so each alternator shares the load. Of course I may forget to switch it back.

Can an ACR be used to join together my starting and house bank?
Can the ACR sense which engine is running or does it only sense one engine running?

I found a 2 source 4 output battery combiner that will do that, but the price is high.
zero volt drop marine battery isolator

An ACR is a simple device. When it sees one side above 13.25 volts it closes the relay connecting the two sides.

So.. Yes you could use it to connect your "second" engine to your house bank to share the load between the two alternators.

The challenge you might run into is that depending on the type of voltage regulatords you have on the alternators they might end up "fighting" and you might not get as much benefit think.

I am also thinking that when both engines are running, the voltage is in the mid 14's when fully charged, and maybe 13.9 when severely depleted.

The ACR is dual voltage sensing, low and high, so it might kick out and do nothing if both engines are running.

The alternators are both one wire Delco 12SI 80 amp rated. Never seems to be a problem joining them using the battery switch.

Maybe I need to create my own ACR which then wont likely be automatic unless I can design my own volt sense circuit. I can imagine a remote controlled relay with manual switch, which is not really any different from me lifting a hatch up to turn a switch, but would be more convenient. I could setup to only have solenoid power if the engine ignition is on and my remote switch is on.

Bluesea ACR are sold for adding a battery to the same engine alternator.

Actually It might work, if it does not sense the other battery bank is fully charged and go open.
High voltage open lockout is 16vdc.
Anyone know for sure?
https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

I sent BlueSea a question with my relevant configuration.

I decided to get this cheap 90 amp continuous relay.

https://www.amazon.com/gp/product/B00KGID0X0/ref=od_aui_detailpages00?ie=UTF8&psc=1

My idea is to join across both banks connecting the positive sides on the battery 3 way switches.
I have electric fuel pump relays, so I can siphon a little power from the fuel pump relay to run the solenoid coil off the port engine, and route it through an unused switch I have on the helm.

So port engine starts, since it charges only the single starting battery, alternator will send most of it's unused power over to starboard battery bank.

And when engine is off, starter bank remains isolated, even if helm switch is on.
So partially automatic. Voltage sensing wont matter too much since the starter battery should be well charged. I also think a fully charged starter bank will be a boost, I will have that and the alternator dumping the power into the depleted house bank.
The fuel pump relay ideally should not come on when engine cranks, it comes on when oil pressure rises, so I may have to pull the fuel pump start wire off the 3 prong oil pressure switch. Since I have an electric priming switch for the pumps, it wont make any operational difference. I would not want the combining solenoid to combine to a depleted bank when cranking to start the port engine.

sdowney717 said:

My situation.
I have 2 engines, so 2 alternators.
I have 3 batteries, one battery is for starting both engines. 2 batteries for house loads.
I have two 3 way switches, so can combine all 3 or isolate all 3 batteries.

Problem is this.
Anchor out for hours. No problem starting engines.
But the house batteries are low, so the starboard engine alternator gets a hefty load like 60 amps to charge depleted house batteries while port engine alternator is loafing charging fully charged starter battery.

It works but sometimes I will manually combine the banks together so each alternator shares the load. Of course I may forget to switch it back.

Can an ACR be used to join together my starting and house bank?
Can the ACR sense which engine is running or does it only sense one engine running?

I found a 2 source 4 output battery combiner that will do that, but the price is high.
zero volt drop marine battery isolator

Click to expand...

Yes a Blue Sea ACR will work perfectly for this. Forget the marketing gimmickry of the Sterling is is not necessary..

CMS said:

Yes a Blue Sea ACR will work perfectly for this. Forget the marketing gimmickry of the Sterling is is not necessary..

Click to expand...

Thanks. I got reply from Blue Sea tech who is an ABYC technician, and he agrees, can be used this way, if joining the alternator outputs is allowed by the alternator company.

He shared 2 configs for doing this, which I have not closely looked at. You will notice 2 ACR's are used. If I did this in my design, I would use just one ACR.

It is funny, but so many configs use 2 starting batteries when all you need is one.
I would rather have 2 house batteries and one starting battery. It is just like starting your car, then turning it off, then starting your car again, works fine. I also have a generator, which can charge batteries through the 3 bank AC charger, so I have lots of options.

Here is my rough sketch out of the DC with two switches.
I moved a house battery to the #2 terminal on the left switch when I finally set that up.

And this diagram is actually a reverse image of what I have, my port has the single starter, and starboard the 2 house batts.

I will put a combining relay across terminals 1 of right side switch, and terminal 1 of left side switch.
My setup fuses the alternator output and is always connected to batteries, but could have used breakers.

I would simply split the house batts , one per engine, and use the rotary to disconnect the start while anchored.

KISS

FF said:

I would simply split the house batts , one per engine, and use the rotary to disconnect the start while anchored.

KISS

Click to expand...

Would also work, except again requires some user intervention to ensure a good starting battery which the continuous duty 90 amp relay will accomplish. Or could use the combiner onto starter battery. But that leaves only one alternator to charge it, not two.

Just thinking, if both house batts completely went dead, I could crank and not start, so I could switch back to having second house to terminal 1. That way 2 dead house batteries could be isolated and start battery is the sole surviving house and start battery. But I never have run them down that far. I just start up the gen if house batteries go too low. I always leave that switch on both. Idea was what if one battery failed, so isolate it from the other house battery. But really then just disconnect the terminal off the battery is best.

My years of car work and dead batteries is that connecting a booster battery to a dead car battery usually starts the car anyway. I think because the discharged battery has so much internal resistance, it does not drag down the boost battery very much, so maybe I will just leave as is. So just set each rotary switch to both, and it will start.

I did run house down to 11.5v measured under a load last time out, and it started fine. But I don't like it going too low, it wears batteries out sooner.

"But that leaves only one alternator to charge it, not two."

Alts have V regulators , so unless the bat is DEAD DEAD DEAD the voltage from one alt will be a tiny bit higher , which will shut down the second.

The best use for 2 alts is to charge 2 batts.

One ACR will do it. Simply place it between the banks and use a model capable of handling the current of either alternator. This assumes the alts are feeding each battery bank directly and only the current of one alternator (80A) can ever pass through the ACR, which should sit between House POS and Start POS. In this case the Blue Sea 120SI (Model 7610) would be a good fit.

What will happen is this:

>Engines start

>Start battery comes up to 13.0V quite quickly, usually within seconds due to SOC, as it is nearly fully charged

>90 Seconds after attaining 13.0V the relay closes paralleling the two banks (at 13.6V paralleling takes only 30 seconds)

>Both alternators can now contribute to the now paralleled battery bank

>Most of the combined alternator current, usually well over 90% of it, will now flow into the house battery charging it faster.

>As the batteries attain the voltage limit of the alternators one alt will drop off-line temproarily.

>If one alt can't supply all the current needed, in early absorption, the other alt will ping-pong along popping back on-line until the voltage superior alt can finish the job.

>Charge sources or alternators are shut down

>DC system loads pull bank voltage back below 12.8V and the relay opens isolating the two banks.

Bulk Behavior:

Adding an ACR between the banks will speed your bulk/constant current charging time. Bulk is the charging duration between alt turn on/excite and attaining the regulators voltage limit. The time spent in bulk, slowly increasing bank voltage, will be dictated by your available current and the SOC you started at. It can be as long as two plus hours, with a small alt, and as short as 10-20 minutes with a large one..


Absorption Behavior:

Absorption is absorption (constant voltage) and nothing you can do will shorten the voltage limited charging stage other than raising the voltage limit. Absorption starts when the battery voltage has been brought up to the regulators voltage limit and we enter the constant voltage stage. Voltage regulators are simply "votage limiters". The time it takes to do this can depend on battery health (sulfation), amperage of charge source and the SOC you started at. The higher the charge current the lower in the SOC curve you attain the constant voltage/absorption stage.

For example a Lifeline Battery charged at .2C and .4C or 20% of Ah capacity and 40% of Ah capacity:

.4C Charge from 50% SOC - Bulk = 19 minutes
.2C Charge from 50% SOC - Bulk = 1:16 minutes

.4C Charge from 50% SOC for 1 Hour = 85% SOC
.2C Charge from 50% SOC for 1 Hour = 71% SOC

As can be seen charge rate makes a big difference in actual stored capacity during short duration charging events. In this scenario an additional 14% of capacity was realized even though bulk was shorter. Not utilizing the energy of your second alternator means it goes wasted. An ACR is an inexpensive, reliable and nearly fool proof solution to make considerably better use of two alternators.

If one regulator limits voltage to 14.41V, even though they may both spec at 14.40V, and the other is 14.39V then the 14.39V regulator will shut down the field until battery voltage drops back to 14.39V or less. In early absorption you may see some "ping-pong" but in bulk both alts will be running full bore unless an internal temp compensation thermistor exists in the regulation system. None of this will damage either alternator.

FF said:

"But that leaves only one alternator to charge it, not two."

Alts have V regulators , so unless the bat is DEAD DEAD DEAD the voltage from one alt will be a tiny bit higher , which will shut down the second.

The best use for 2 alts is to charge 2 batts.

Click to expand...

I guess I need to read some about that.

My boat tells me different story.

Lets say, starboard alternator is charging 2 depleted batteries, ammeter reads 60 amps, port alternator is charging starter battery at 15 amps. system is not interconnected.

When I manually turn bat switch to combine both sides, the starboard alternator ammeter output drops back to say 30 and the port alternator ammeter jumps up to 30.

I have done this a lot so I see it happen.
I have one wire alternators Delco 12SI 80 amps.
So leads me to believe both alternators that I have in particular, will share the load without dropping out. I dont know what else to say why.

Are not Lifeline batts AGM not LA batts that have a limit to charge rate , or will overheat?

THe charge rate has to be limited to the batt type many LA are limited to 10% -15% or so of capacity .

2 alts might help with a 1000A batt bank but might not help with a 400Amp set of 4 golf carts?

"I have one wire alternators Delco 12SI 80 amps."

These are built and regulated to charge almost full car batts., not half dead deep cycle batts.

A 3 or 4 stage V regulator will reduce the charge time to the minimum for your batt type.

sdowney717 said:

I guess I need to read some about that.

My boat tells me different story.

Lets say, starboard alternator is charging 2 depleted batteries, ammeter reads 60 amps, port alternator is charging starter battery at 15 amps. system is not interconnected.

When I manually turn bat switch to combine both sides, the starboard alternator ammeter output drops back to say 30 and the port alternator ammeter jumps up to 30.

I have done this a lot so I see it happen.
I have one wire alternators Delco 12SI 80 amps.
So leads me to believe both alternators that I have in particular, will share the load without dropping out. I dont know what else to say why.

Click to expand...

Both alternators will contribute in bulk. Once absorption is attained they will ping-pong until one alt can finish the job..

One wire alternators are really a very poor choice for a marine charging system due to wire runs and voltage drop. The lack of proper voltage sensing is the real issue, but they can be used in parallel to shorten the bulk charging times. The 12SI can pretty easily be converted to external regulation too.

CMS said:

Both alternators will contribute in bulk. Once absorption is attained they will ping-pong until one alt can finish the job..

One wire alternators are really a very poor choice for a marine charging system due to wire runs and voltage drop. The lack of proper voltage sensing is the real issue, but they can be used in parallel to shorten the bulk charging times. The 12SI can pretty easily be converted to external regulation too.

Click to expand...

Yes it can be converted.
I get a good 14.5 vdc reading which is good output. I have dual digital volt meters in my panel.
I measure the voltage where the alternator wires enter into the helm wiring panel after about 7 feet of 6 gauge wire from the alternators. I have not noticed any weird low voltages at the batteries when measured at their posts.

The one issue they do have is the need to rev up to register a charge, because they are self exciting.

Another thing, boat used to have ammeters up on the flybridge, Egg Harbor ran realy long wires out the alternators, to get ammeters up on the bridge, then ran back down to batteries.
I ripped that out and shortened the charge wiring by at least half. Replaced ammeters up there with volt meters.

I kept the lower helm ammeters and added two digital vdc meters. Cheap off ebay and work well.

I wanted to turn them off and on with a small push switch out of a computer. So I ran the positive wires to the battery +, and ran the black grounds tied together common through the single switch to gound, works well.

"Would also work, except again requires some user intervention to ensure a good starting battery which the continuous duty 90 amp relay will accomplish.'

This is how RV have been doing it for 6-7 decades.

To make zero knowledge or work from the operator , they use key switches with an ACC position.

The alt is wired to the start , and when ACC power comes from the key switch , the house is joined.

The solenoid is under $20 at the RV place and Cole Hersey makes quality marine key switches with an ACC terminal.

One simple trick while at the power pole is to turn the key switch to ACC overnight every few weeks to charge the start batt , if you do not have a shore multiple output charger.

Key switch charge control is the ultimate KISS .

I essentially have the same setup with a single start battery for twin engines and a house bank. I eliminated the original wiring and ammeters and cabled the alternator charge directly to the batteries. Stbd to house (600+ AH) and port to start (single Group 31). I have a SOC meter on the batts.

I installed a 160A Yandina Combiner to share the house charge requirements with the start-side (port) alternator. This combiner is selectable with a helm SPDT switch. When the house needs a bulk charge, the combiner is set to ON and the port alternator helps with the charge. When the banks reach absorption and the port alternator starts to drop out, then cycles ON-OFF (tach drops off), I turn the combiner off and allow the alts to split duties in topping off their respective battery. This restores normal tachometer function as well.

My stbd alternator is a Balmar 120A externally regulated to 100A. The port alternator is a standard 55A internally regulated. Here's an old copy of my schematic. It's been modified slightly over the years with different stbd alternator, charger, batteries and inverter, but the layout remains the same and functions very well for my purposes.

Best of all, it's simple, essentially effort-free and reliable. No switches to remember with each start or shutdown.

PS. I sketched this out as I look at the system from inside the ER so the port and stbd appear reversed in this schematic.

FF said:

"Would also work, except again requires some user intervention to ensure a good starting battery which the continuous duty 90 amp relay will accomplish.'

This is how RV have been doing it for 6-7 decades.

To make zero knowledge or work from the operator , they use key switches with an ACC position.

The alt is wired to the start , and when ACC power comes from the key switch , the house is joined.

The solenoid is under $20 at the RV place and Cole Hersey makes quality marine key switches with an ACC terminal.

One simple trick while at the power pole is to turn the key switch to ACC overnight every few weeks to charge the start batt , if you do not have a shore multiple output charger.

Key switch charge control is the ultimate KISS .

Click to expand...

I am planning on using my oil pressure switch for the fuel pump to activate the relay.
And use an on-off helm switch to be able to disconnect manually. Nice thing is I added a white handled carling breaker switch at the bottom of the row of vertical white handled carling switches and wondered what to do with it years ago, now I found a use for it.

Connected this all together today, and it works fine. I like it a lot.
Best thing is the way I am using this relay will save wear and tear on the alternator of the starboard motor since the port alternator is now joined in output to the starboard alternator when the switch is on and the port motor starts.

When I start the port motor and turn on the relay, I see the port alternator output jump up on the ammeter
.
I plan to leave the switch on all the time.

Next time out will see how this arrangement does with a depleted starboard bank.
My guess is no different from me manually rotating the battery switches, I really like it being automated so I don't have to think about it as much.

And I have been doing this manually for over 10 years joining alternator outputs with no ill effects.

You might find that with the switch on and the batteries at 100%, your weak side alternator might stop feeding the tachometer. When this happens on mine, I either increase the electrical load or, more commonly, deselect the combiner to split the sides.

Glad to hear it's working for you.