Anyone use an ACR?

[Dave_E]

Hi All,

The good ship came with an ACR (Automatic Charger Relay), something I've never seen before. Took me awhile to figure out what it did. Check me if I'm wrong, but it sort of looks like a "cheater" for charging all your batteries. All my past boats have had chargers that go to each battery (group 27's). Now I own this monster that has an 8D, and (4) 6V batteries. I have an old Trace Engineering charger/inverter (now called Xantrex) that has a pair of serious cables going to the 6V battery bank. Up at the battery switch... the ACR basically jumps the feeder from the 6V bank to the 8D for charging.

Do any of you have an ACR? Any problems?

Dave

 

[DavidM]

An ACR or automatic charging relay does exactly what you say: connects the house to the starting batteries to charge both, but disconnects them when there is not an active charging source to protect the starting battery from running down on the hook. The other benefit is that it does the same thing with any charging source, particularly your engine alternator but also solar panels.

The simple ones are based on a voltage sensitive relay that pulls in at about 13.2 volts and drops out at about 12.8. Those are very robust and rarely fail. The more sophisticated ones like from Blue Seas are electronic and sometimes provide a different charging profile to the connected battery bank. I don't have any experience with these.

ACRs unlike the typical 1,2,all switch are a set and forget solution to battery charging and on-the-hook isolation. Everyone who anchors out a lot should have one or a similar device like an Echo Charger.

David

 

[Cigatoo]

DJ, On the same topic I think, I have a trusty old 1 2 Both Off switch that works fine. But as a gadget lover I was thinking of adding an ACR. Would you recommend that I remove the existing switch when adding the ACR? Or keep the switch and run in “Both” with the option to turn the batteries off when necessary. I have no heavy 12v loads. Just simple nav equipment a radio and a few lights. Also I currently have a Guest 5 amp dual batter charger that is wired directly to each battery so as currently wired the ACR would have no effect on the charger. I appreciate your thoughts.

 

[aboatman]

I think most serious cruising boats would be equipped with an ACR. It does what the conventional switch does for charging but automatically.

Easting, the ACR only works for charging. It won't allow you to turn the power off or combine both batteries for engine starting. An "off"/"on" switch for each battery is a good idea. You could add another switch to combine the batteries for emergencies or carry a jumper cable. Or join TowBoatUS or SeaTow.

 

[DavidM]

DJ, On the same topic I think, I have a trusty old 1 2 Both Off switch that works fine. But as a gadget lover I was thinking of adding an ACR. Would you recommend that I remove the existing switch when adding the ACR? Or keep the switch and run in “Both” with the option to turn the batteries off when necessary. I have no heavy 12v loads. Just simple nav equipment a radio and a few lights. Also I currently have a Guest 5 amp dual batter charger that is wired directly to each battery so as currently wired the ACR would have no effect on the charger. I appreciate your thoughts.

I would prefer to delete the 1,2,all switch and replace it with a simple on/off switch for each bank. Wire the engine alternator to charge the house bank because that is the one that needs the most charging. Use the ACR to combine that bank with the starting bank once the engine is running and charging.

If you want to easily combine the two banks (so that you can use the house batteries to start the engine) then install a third on/off switch for this purpose.

I believe that an ACR should be a set and forget system and the switches described above are for emergency use (turn the switches off if any fire) or unusual situations (like combining to start the engine with the house bank).

And yes a dual output charger doesn't need the ACR. It will charge each bank independently of an ACR. But the ACR is needed for the engine alternator output.

David

 

[Cigatoo]

I would prefer to delete the 1,2,all switch and replace it with a simple on/off switch for each bank. Wire the engine alternator to charge the house bank because that is the one that needs the most charging. Use the ACR to combine that bank with the starting bank once the engine is running and charging.

If you want to easily combine the two banks (so that you can use the house batteries to start the engine) then install a third on/off switch for this purpose.

I believe that an ACR should be a set and forget system and the switches described above are for emergency use (turn the switches off if any fire) or unusual situations (like combining to start the engine with the house bank).

And yes a dual output charger doesn't need the ACR. It will charge each bank independently of an ACR. But the ACR is needed for the engine alternator output.

David

Got it thanks. Forgot about being able to combine them. I Greatly appreciate your input.

 

[AusCan]

I have a Blue Seas ACR. https://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A/FAQ

My charger and alternator are connected directly to my house bank. The start battery is charged via the ACR. It is a completely set at forget system for charging both banks via the mains charger, alternator or solar panels when it senses a voltage >13V. It then isolates the batteries when the power is drawn and voltage drops to 12.75 volts.
I still have a 1/2/both switch but it is only to back up power to the engine starter if ever needed.

Simple, cheap and foolproof.

 

[Bacchus]

I installed a version of the ACR to allow alternator charging of my thruster batty and house / start bank.
See the Charging System Mods here for specifics of the system I installed.
So far it has worked as planned and I have had zero issues.

As outlined I also installed a 1/2/all/off batty sw to allow emergency connection of my gen batty w/ the house / start bank - provides assist either direction depending on situation - have never had to use it - YET.

 

[Insequent]

I have 2 Blue Seas ACR's and 3 of their RBS. This enables charging of two start batteries and the house bank, and paralleling start batteries and house. I'll try and attach a schematic, although file size is large.

For charging I have a 200 A alternator on each engine, connected via a Balmar 612 and six 345 W solar panels connected via Outback FlexMax 80 solar controllers.

It has all worked flawlessly for the last five years. The one thing I did start doing a few years ago was turning the ACR's to "off" when I anchored, and then back to "Auto" when the engines were running. The reason was that they made quite a loud noise when they switched, which they did frequently as house loads turned on and off while at anchor. They were spoiling my peace and quiet!

 

[Ken E.]

I also use two Blue Sea ACR's and my setup is like Insequent's. I've used them for five years without a burp. Great product.

 

[kchace]

I've used Blue Seas ACR's on my last 2 boats with great results and no issues whatsoever. I have 2 on my current boat.

Ken

 

[CaptTom]

Is there any concern that an ACR will over-charge one bank?

Say the house bank at 50%, but the starting bank almost 100%. Presumably the alternator would be driving a pretty high charging voltage. This could go on for hours. Would that hurt the starting bank?

 

[Cigatoo]

Is there any concern that an ACR will over-charge one bank?

Say the house bank at 50%, but the starting bank almost 100%. Presumably the alternator would be driving a pretty high charging voltage. This could go on for hours. Would that hurt the starting bank?

Based on my reading it does nothing to regulate the charging rate. It just opens and closes the charging path to the second battery. The regulator / alternator still does its job as normal.

 

[Dave_E]

Good discussion All,

As usual, learning has taken place. Other than some sloppy wiring to work on, the good ship came with 2 alternators, an 8D and 4 6V batteries, a generator, monster charger/inverter and of course shore power. Quite a bit more than I've ever had before, so had some learning to do. Thanks for the insights!

Dave

 

[Tom.B]

K.I.S.S.

My system is like AusCan’s. With both alternators to house bank of 8 6v and ACR to the start bank of 3 12v dualies. The Blue Seas ACRs are very reliable and I can’t imagine them failing. Never use a 1/2/B/O switch... never ever... for charging. It is far too easy to forget to switch it when you need to and it WILL leave you stuck at some point.

 

[kchace]

Is there any concern that an ACR will over-charge one bank?

Say the house bank at 50%, but the starting bank almost 100%. Presumably the alternator would be driving a pretty high charging voltage. This could go on for hours. Would that hurt the starting bank?

People who don't understand how batteries charge worry about it all the time but its not a problem as long as all of the batteries are of the same type. A battery that is more fully charged than another needs a higher voltage to push current into it. The battery with the lower charge keeps the charge voltage lower by accepting the current at the lower voltage.

Ken

 

[DavidM]

Is there any concern that an ACR will over-charge one bank? Would that hurt the starting bank?

In practice, no. But some ACRs have sophisticated settable charging algorithms for the second bank if that bothers you.

A cheap, under $100 charging relay such as from Yandina, or Blue Seas cheapest ACR will work just fine.

David

 

[john61ct]

Starters require hardly any charging at all, are usually cheap and robust plain lead-acid chemistry.

If your Starter batt is

very expensive, and/or

requires a completely different *voltage* setpoint than House,

then you may want to spend the money on a DC-DC charger for Starter rather than using an ACR/VSR/combiner.

Otherwise, don't worry about it.

All significant charge sources should be wired to House directly and configured for that banks' needs.

 

[john61ct]

some ACRs have sophisticated settable charging algorithms for the second bank

No, if they do, they're no longer an ACR (VSR/combiner).

You must be thinking of DC-DC chargers.

The Sterling-designed ProIsoCharge units prey on this misplaced concern, ask a lot of (IMO wasted) money to "solve" this non-problem.

But they are not at all adjustable.

 

[john61ct]

A battery that is more fully charged than another needs a higher voltage to push current into it. The battery with the lower charge keeps the charge voltage lower by accepting the current at the lower voltage.

No given proper wire sizing, voltage is the same across the circuit and all batts on it.

The reason this issue is not a problem is that lead batts' SoC and internal resistance cause them to self-regulate their acceptance of **current**, accepting less as they get to Full.

 

[john61ct]

This unit https://www.bluesea.com/products/7620/ML-ACR_Automatic_Charging_Relay_-_12V_DC_500A

is the bees' knees, never have to replace it no matter how big an alt you put in, never fails, includes starter isolation even for dual engines, and offers self-jumpstarting from House at the press of a button

 

[Delfin]

Is there any concern that an ACR will over-charge one bank?

Say the house bank at 50%, but the starting bank almost 100%. Presumably the alternator would be driving a pretty high charging voltage. This could go on for hours. Would that hurt the starting bank?

Under that scenario, the ACR will isolate the banks and only charge the house bank, assuming it is wired as the primary bank. Once the voltage of the primary bank rises to a point that indicates the house bank is about fully charged, the ACR will combine the two banks and charge both but at that point charging current is much reduced.

 

[C lectric]

Yes.

 

[john61ct]

Under that scenario, the ACR will isolate the banks and only charge the house bank, assuming it is wired as the primary bank. Once the voltage of the primary bank rises to a point that indicates the house bank is about fully charged, the ACR will combine the two banks and charge both but at that point charging current is much reduced.

100% false.

When an ACR senses charging voltage it connects the two circuits. It does not charge anything.

When charge source stops it isolates them

That is *all* it does, ever ; it is an automatic Both switch, full stop.

Some of what you say may sometimes happen, depends on many variables, but nothing to do with the ACR.

Different ACRs may have slightly different setpoints, delays to stop chatter etc, but combining happens many many hours before House is Full.

 

[Insequent]

Here is what my Blue Seas ACR does - quote from Blue Seas site:

Automatic Charging Relays - ML-ACRs
500 Amp magnetic latching (bi-stable) relay automatically combines batteries during charging and isolates batteries when discharging and when starting engine.

I'm not sure of the discharge current trigger point, but it is likely just a few amps such as the reefer draw. Hence the switching on/off I noted previously.

 

[john61ct]

There is no measuring or detection of current flow (amps) in either direction.

The combine-or-isolate "logic" is 100% purely based on voltage level only.

True for every ACR / VSR / combiner ever since Ann-Marie Foster of Yandina Ltd invented the first one.

 

[Insequent]

There is no measuring or detection of current flow (amps) in either direction.

The combine-or-isolate "logic"is 100% purely based on voltage level.

Ok, thanks for clarifying. Makes sense. The reefer might give a momentary voltage drop when starting to cause the switching I see. From memory it is only when the reefer cycles off that the banks combine again.

 

[john61ct]

With a bigger/stronger bank, e.g. LFP, or heavier gauge wire, that may reduce the drop.

 

[Delfin]

As they say, 100% false.

100% false.

When an ACR senses charging voltage it connects the two circuits. It does not charge anything.

When charge source stops it isolates them

That is *all* it does, ever ; it is an automatic Both switch, full stop.

Some of what you say may sometimes happen, depends on many variables, but nothing to do with the ACR.

Different ACRs may have slightly different setpoints, delays to stop chatter etc, but combining happens many many hours before House is Full.

You have one on your boat that you've been using and observing for 12 years, John?

Here is what Blue Sea says an ACR does:

"ACRs or Automatic Charging Relays are automatic switches that close when the voltage on one of the batteries rises to a level (normally 13.2V to 13.7V) indicating the battery is connected to a charge source and is partially or fully charged. The switch then closes and shares the charging current with the other battery until the voltage drops to some lower level (normally 12.4 to 13.1 depending on model) and the switch opens. This prevents discharging both batteries when there is not enough current to charge both batteries."

They could also mention that this directs the full charge current to the primary battery bank. Until it is full or nearly so, the circuit between the two banks is open. Once the primary bank's voltage rises to the correct level, the circuit closes so the secondary bank is charged along with the primary.

Oddly enough, that is precisely how my, and I assume every other ACR on the planet, functions.

 

[Delfin]

This may also be helpful, from the installation manual:

Contact Circuit Voltage 16V DC Max. 32V DC Max.
Relay Contact Position:
-Combine (30 sec.) 13.5V 27.0V
-Combine (90 sec.) 13.0V 26.0V
-Open Low (10 sec.) 12.35V 24.7V
-Open Low (30 sec.) 12.75V 25.5V
-Open High 16.2V 32.4V

As shown here, on a 12v system, the batteries are only combined with the primary bank has reached 13.5v for 30 seconds or 13 volts for at least 90 seconds. Once the circuit closes and the banks are combined, both banks are charged. On discharge, once the primary bank reaches 12.35 volts for 10 seconds or 12.75 volts for at least 90 seconds, the switch opens again, isolating the batteries and preventing both from discharging.

And, if the voltage regulator goes rogue and stops limiting charge voltage, the unit will also isolate the batteries again if 16.2 volts is reached, meaning you might fry your house bank, but you could still start the motor from the starter bank.