ACRs and Two Bank Battery Chargers

[djgarrett]

Hi everyone -

I think this may be my first post on the forum; I've read and studied the collective wisdom here for some time, but have not seen any discussion about this:

I have a small Guest 2-bank battery charger for my sailboat's 2 bank system. Typical house/start arrangement. I have also a BlueSea ACR to enable charging the house battery when under power. When the motor is on and want to get some charging to the house side I'll connect the ground wire to the ACR.

Can I keep the ACR in it's enabled mode (grounding the ACR to allow the relay to flip) when the battery charger is on shore power without damage to the charger? Or, should I switch to a single-bank charger and let the ACR handle charging both sets of batteries?

The Guest charger is one of the older 5/5 systems, I'm thinking about getting a new charger because it takes a while to recharge at only 5 amps. Most of the chargers I've looked at capable of handling a 230ah/75ah set up (house/start) have 2 or more bank charging capability, and I'd like to stop digging around in the bowels of the boat to connect the ACR just to take advantage of charging a bit while underway.

I'm interested in what y'all think. It's easy to ground the ACR when I need to, I know, but when I'm sailing I'd rather focus on having a good sail! Thanks!

s/v Roma
Oriental, NC

[Watermann]

You should be able to leave the ACR "online" at all times, regardless of the charging source. The whole concept of the ACR is that one bank (your house bank) has all charging sources (alternator, AC batt charger, solar, etc.) run directly to it and the ACR closes and opens to keep the other bank/battery (engine start bank) charged/topped-off.

The opening & closing logic of the relay is posted on Blue Sea's website (should also be in your manual, if you have it).

All this being said, even with a two/three bank charger, you still only run one out of the charger outputs to the house bank. The sole source of charging the engine bank is via the ACR. Multi-bank chargers are rated for their total output - not per bank (ie, a three-bank, 30A charger is rated for 30A total - not 30A per bank).

A 5A charger is quite small. For your batt capacity, you should have at least a 30A.

[Salty Mike]

If you want to keep the setup ypu have why not add a switch for the ground wire? Or if you wanted to get fancy use a relay energized from the ignition switch.

[HappyMdRSailor]

Welcome to CF dj !

As above, I don't understand the logic of disconnecting the ACR...

AND OMG... you need a bigger charger... Lots of electrical gurus here... They'll chime in...

[djgarrett]

I agree! OMG, I need a bigger charger!

Thanks for your thoughts. I was disconnecting the ACR while charging on shore power because I couldn't find any info on whether the ACR would interfere with (or possibly damage) the charger or the batteries while it's cycling through the different charging stages - for example, if the house was needing more charging than the start, I was concerned the ACR would prematurely set the charger into float before the house battery was fully charged.

If I'm only connecting one bank output from the charger to the house battery, can I connect more than one input to the same battery? For example, if I get a 30 amp charger (15 amp each bank), I can I connect both "bank" outputs to one battery for a total of 30 amps of charging to the house battery and let the ACR handle the rest?

Wow, re-reading that it sounds like a dumb question... but it is what it is.

[Stu Jackson]

Read these:

Welcome To MarineHowTo.com Photo Gallery by Compass Marine How To at pbase.com

Electrical Systems 101 Electrical Systems 101

Use only one output and direct ALL charging sources to your HOUSE bank, not the reserve bank.

[Chuck Hawley]

Originally Posted by Watermann

You should be able to leave the ACR "online" at all times, regardless of the charging source. The whole concept of the ACR is that one bank (your house bank) has all charging sources (alternator, AC batt charger, solar, etc.) run directly to it and the ACR closes and opens to keep the other bank/battery (engine start bank) charged/topped-off.

Not sure I entirely agree with this. One of the advantages of charge parallel solenoids is that it doesn't matter a lot where you have the charge sources hooked up. For example, if you have a small diesel with an OEM alternator which is connected to the nominal starting battery, you can just leave that connected and not run the output to the house bank. Yes, conceivably you'd be better off charging the house bank "first", but you don't have to.

Originally Posted by Watermann

All this being said, even with a two/three bank charger, you still only run one out of the charger outputs to the house bank. The sole source of charging the engine bank is via the ACR. Multi-bank chargers are rated for their total output - not per bank (ie, a three-bank, 30A charger is rated for 30A total - not 30A per bank).

This varies with the design of the charger. Some smaller chargers use "modules" that have no interconnection so they can charge either 12V or 24V banks, or they can charge batteries with different chemistry since they can be set to different setpoints. Each leg will put only on what it's power supply is rated for. These can be identified by having separate + and - connections for each leg (generally). This is generally true with encapsulated waterproof chargers (again, generally.)

So, by paralleling the output of these smaller chargers, you can get the full rated output of both (or all three) banks into a single bank.

Originally Posted by Watermann

.A 5A charger is quite small. For your batt capacity, you should have at least a 30A.

I get that a larger charger is better under two conditions, but not necessarily under all conditions.

1. If you have high house loads, say on a liveaboard boat with tons of lights, then you'd obviously want a charger that is greater than the ambient loads.

2. If you return to the dock with depleted batteries and want to depart quickly with fully-charged batteries.

Otherwise, I think we've frequently been sold oversized chargers for average use. I think that the formula (nominal loads + 10% of battery capacity) would work for virtually all sailors.

Cheers,

Chuck

[btrayfors]

(from Chuck) "Otherwise, I think we've frequently been sold oversized chargers for average use. I think that the formula (nominal loads + 10% of battery capacity) would work for virtually all sailors.

Cheers,

Chuck"

I'm a bit surprised by your statements, Chuck, particularly as you are a "Marine Service Provider"

1. The OP has 300AH total battery capacity. He has a 5A charger. That's unlikely to be large enough to handle even modest normal loads, much less do efficient charging.

2. Even your formula would suggest that 10% of 300AH = 30 plus nominal load (say 5A) would call for a minimum 35A capacity charger.

3. You can't have a charger which is too large. Let me repeat that: You can't have a charger which is too large. With modern "smart chargers" the batteries will accept what they're going to accept at any state of charge and temperature, period.

4.The difference in price between a 30A charger and a 50 or 60A charger is quite small, and in the larger scheme of things inconsequential.

5. You're not going to get a quick turnaround at the dock and depart with a "full battery", no matter the size of your charger. It takes many hours to reach full charge because a battery's acceptance rate drops dramatically as the SOC increases.

Bottom line on best strategy:

1. Hook all charging sources directly to the house batteries;

2. Use a voltage follower device (EchoCharge or DuoCharge) or an ACR to keep the start battery topped up;

3. Get a modern smart charger of considerable capacity; you can't size this too large.Don't worry about switching anything or hooking up anything. This arrangement is fully automatic and will provide optimum battery charging.

Bill

[btrayfors]

This diagram illustrates my "bottom line" recommendations in the previous post.

It is simple, clean, and reliable. Has worked perfectly on my boat for the past 10 years, and on many of my client's boats.

This diagram makes use of the 1-2-BOTH-OFF switch found on many boats, and just adds another ON-OFF switch. It can also be implemented with three simple ON-OFF switches (like the Blue Sea Systems #6006 switch), as in the second graphic.

Bill

[Snore]

Take a moment and read the following manual from Blue Seas. You should be wired this way.

http://assets.bluesea.com/files/reso.../990310020.pdf

[djgarrett]

Thanks guys. I have it wired exactly as the manual from Blue Seas provides, with the exception of the charger (which isn't accounted for in the Blue Seas manual at all). Instead of a switch on the ACR ground wire, I just disconnect the spade terminal, which has the same effect as a switch.

The charger is connected as the Guest manual provides, which has positive and negative leads for both banks.

I've been "yanking the ground wire" solely because the Guest charger manual likewise doesn't account for an ACR, and my concern is that (1) it's not clear to me whether the multi-stage charging is independent of the banks (in other words if the house side needs more charging than the start, the start goes into float while the house keeps charging - however a volt meter check confirms that this does not happen, which in retrospect does nullify this concern); and (2) if I kept the ACR in, that I'd be cooking the start battery while the house is still accepting a charge.

From what it sounds like, once I get a bigger charger if it has multiple banks, I'll hook all banks to the house (all charging only to the house side, which includes modest solar in my instance) and let the ACR do its thing.

I love the discussion - so much to consider! Thanks again!

[mitiempo]

Originally Posted by djgarrett

...... and my concern is that (1) it's not clear to me whether the multi-stage charging is independent of the banks (in other words if the house side needs more charging than the start, the start goes into float while the house keeps charging - however a volt meter check confirms that this does not happen, which in retrospect does nullify this concern); and (2) if I kept the ACR in, that I'd be cooking the start battery while the house is still accepting a charge.

You will not cook the start battery by leaving the ACR in (combined). This is the same way an ACR works when all charge sources are connected to the house bank. Once the house bank reaches the combine voltage - about 13 volts - the ACR closes and the start battery gets charged. As long as the house bank is being charged, for hours in many cases, the start battery is exposed to the current because the ACR is closed even though the start battery will likely be at full charge in a very short period of time. This will not damage the start battery.

[Snore]

I just finished installing the same thing in my boat.

First, as you did- it is wired to the Blue Seas diagram.

Second- I recall reading somewhere on Blue Seas, or it being implied- my battery charger is only charging the house. The logic is that since all the domestic load is on the house batteries, charging them allows the load to be replaced by the charger. If you charge both the house and engine, it is possible to put a sudden load on the house (i.e. Cooler), for the voltage to drop on the house and for the ACR to open. Then you have one leg of the charger replacing the power being used. Since most chargers deliver a max of 50% of thier rated output on each leg, you have 5 watts going into the battery.

Whereas having both legs of the charger on the house side allows the full output to cover the domestic load. When there is no significant loads, the "normal" state, the battery banks will be combined and they will both be topped off.

Disclaimer: my charger instructions allowed and even suggested running both leads to one bank, if no other bank was present. Be sure to read your charger instructions.

We are all assuming that both the house and starter batteries are the same type.

[ramblinrod]

OK, as another marine service provider, I don't agree with much of this.

Responses in red.

Originally Posted by btrayfors

Bottom line on best strategy:

[/B]1. Hook all charging sources directly to the house batteries;

When using different battery technologies for different banks, and the shore power charger is capable of different charging algorithms per bank, it is better to use this, than supply the house bank algorithm to the start battery (esp. if house bank is lead acid, and start is something else).

2. Use a voltage follower device (EchoCharge or DuoCharge) or an ACR to keep the start battery topped up;

If the vessel is equipped with a 1/2/Both/Off switch, and the owner prefers this, there is no need to change.

3. Get a modern smart charger of considerable capacity; you can't size this too large.Don't worry about switching anything or hooking up anything. This arrangement is fully automatic and will provide optimum battery charging.

Consider bank size, technology, charge cycle, and recharge rate to select the "appropriately sized" charger.

The Tim the Tool Man approach is not necessarily the best approach. A 100 A charger on a 100A-hr lead acid battery (that is only capable of accepting 25 A when it is most hungry, and usually far less, is a huge waste (capacity, charger cost, cable cost).

Bill

To the OP, as others have stated, there is no need to switch the ACR in and out, if connected properly.

[HappyMdRSailor]

Originally Posted by djgarrett

From what it sounds like, once I get a bigger charger if it has multiple banks, I'll hook all banks to the house (all charging only to the house side, which includes modest solar in my instance) and let the ACR do its thing.

I love the discussion - so much to consider! Thanks again!

Glad you're enjoying the discussion... A TON of info to organize here...
Newer generation chargers have it in spades over older brute force charging...

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