Automatic Charging Relay Question

tadslc · Oct 3, 2010

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Can you use a 3-step alternator regulator with an ACR? I haven’t found any info regarding this but I’m concerned that when the regulator goes into float mode it will effect the second bank that’s connected to the ACR.

Thanks

Stu Jackson · Oct 4, 2010

The only purpose of an ACR is to automatically parallel two different banks from a single charging source.

Regardless of whether the source is from an alternator, shorepower charger, or solar wind, etc., that's all it does.

The answer is yes, it'll work with a regulator, and float voltage is well above the ACR initiation voltage anyway.

While you're at it, take the second shorepower charger wire off your reserve bank, if you have it wired that way. The ACR will do all the work.

tadslc · Oct 4, 2010

Thanks Stu, that's what I figured just wanted to double check.

I'm going to separate the two banks and want to make sure that both banks will get charged well.

I was planning on taking off the shorepower charger from the reserve bank.

Loren Beach · Oct 4, 2010

This is interesting and possibly educational for me.
Early this season I replaced an old two bank charger with a new three bank model (that's that way it comes, output wise).

Reading the manual (stop laughing...) I find that it wants any unused output terminal to be paralleled with one in use. i.e. The three outputs for my present two banks are : #1 to the first bank, and #2 and 3 with a jumper wire to the other bank.
So.... if I were to put in an ACR someday, would I then put all three outputs to either bank? And, the ACR would then then "split" the output to both banks?

Who me, confused easily?

This "ACR" stuff interests me because we will be relying a lot more on the engine for charging when we go summer cruising into the San Juan and Gulf Islands in a year or two. Lots of anchoring out or places with no handy shore power.

Maine Sail · Oct 4, 2010

Loren Beach said:
And, the ACR would then then "split" the output to both banks?

The ACR does not "split" it combines banks just like flipping a 1/2/BOTH/OFF switch to BOTH. Once connected they become one large bank that charges. You are better to use a single output charger with an ACR but with an Echo type charger it is required.

Using a dual output charger can cause the relay to close prematurely as the start battery voltage is almost always at or near full so it reaches the "combine" voltage quickly. I have seen instances where the shore charger of say 20 amps is splitting it 10A & 10A. The relay combines because the start bank voltage told it to but then the LARGE house bank quickly sucks the voltage back down below the connect voltage and the relay cuts out. It then cuts back in and out a few more time until the house bank voltage stops sucking it down.

Here are some commonly asked questions from the Yandina site. They invented the automatic combining relay back in 1994.
Q Will banks of different sizes get fully charged?

A Yes, since the combiner just places batteries in parallel, they are all at the same voltage. The charge level of each battery is a function of voltage, so they will all receive the same level of charge. The actual charge capacity is governed by their size, age, chemistry and condition.
Q Won't the smaller battery get overcharged if put in parallel with a large one?

A The whole process of charging batteries in parallel is naturally self regulating, naturally governed by terminal voltage and current flowing through the internal equivalent resistances. For simplification, each battery can be considered as a perfect battery that holds the charge combined with a series resistor representing the internal resistance, and a parallel resistance representing the self-discharge leakage current.
Lets say you have a charging source dumping out say 100 amps. If you have 4 batteries in parallel sharing this source the distribution of the charge current is governed by those internal voltages and internal resistances. From Ohm's law, the charging current that flows into each battery is the voltage divided by the resistance. In this case the voltage is the charging voltage arriving at the terminals minus the actual internal voltage divided by the series resistance of the battery. A discharged battery is going to put a larger voltage differential over the internal resistance so more current will flow to it. A charged battery is going to put less voltage drop across the internal resistance so it will take less or none of the available charging current. A large plate battery which has a correspondingly lower internal resistance will demand more current because of this lower resistance. A small motorbike battery in parallel will have a high internal resistance and demand very little current.

All these demands for current result in a common voltage on the parallel circuit which is what the alternator or charger sees. None of the batteries will ever be "overcharged" as a result because the charging voltage is controlled. Even the smallest battery will only be seeing the same voltage so it is like the other batteries are not there. If you suddenly removed all the big ones and left just the tiny bike battery on the 100 amp alternator, the voltage would immediately rise because the amps trying to flow into the tiny battery have to pass through its internal resistance which is high. But instead of the voltage or current going to an excessively high value, the regulator in the alternator cuts the current back to a level that limits charging to a safe level.

Q How does it keep from over charging a battery? One bank needs a charge and the other does not. As I read your description of operation I don't see where it will not over charge the charged bank.

A When the batteries are in parallel they are at the same voltage because they are connected together.

If they are at the same voltage one cannot get over charged without the other getting overcharged. To overcharge one battery would it would have to be above maximum allowed voltage but if they are in parallel, then both batteries would be above maximum voltage and the charger will shut off.

When the Combiner first closes, the voltage is already above 13 volts. The fully charged battery would have been at 12.8 volts prior to the Combiner closing. So even though it has 13 volts on it, there is virtually no current flowing into it and the battery that needs charge will be taking nearly all the current.

Regards,
Yandina

Q I highlighted a section of your message. If a battery is weak and not taking much of a charge then isn't there a chance the good battery will eventually be boiled dry or at least potentially or is there a safe guard for that built into the unit? Dose it sense the internal resistances? I would like to purchase several of these but need these concerns addressed.

A This is an old and very common misconception of how charging works. Think about it for a moment. You said "Isn't there a chance the good battery will eventually be boiled dry or at least - - "
The only thing that boils a battery dry is overcharging. Batteries start to overcharge and "boil" when the charging voltage gets to 14.2 volts and above. So if the voltage is above 14.2 you are starting this overcharge process. But the voltage is coming from the charger and the charger will stop charging at 14.2 and drop back to a maintenance voltage of about 13.6.

So if one of the batteries was to overcharge its voltage would have to be above 14.2. If the voltage on one is above 14.2 then the voltage on the other is above 14.2 since they are joined together. If the voltage on both is above 14.2 then the charger is faulty. A Combiner can't make the voltage on one battery get higher than the other, it can only make them equal.

You need to stop thinking that a charger puts out current that has to go somewhere. A 20 amp charger rarely puts out 20 amps. All it does is put out voltage, the amount of current that flows is governed by ohms law. Current = voltage/resistance. In the analysis for each battery, the voltage is the voltage on its terminal coming from the charger minus its internal charge voltage. For example, say 14-13 or about 1 volt. The resistance depends on the size of the battery and its condition. So using a resistance of 0.1 ohms the current flowing into the battery is 1/0.1 = 10 amps. A smaller or damaged battery will have a higher internal resistance so the current it takes would be 1/0.5 = 2 amps. As its internal voltage rises, the voltage difference gets less, so if its charge is up to 13.5, current = 0.5/0.5 which is down to 1 amp.

A 20 amp charger doesn't force 20 amps into the batteries so that the unused current from one battery has to go to the other, it puts out a voltage and each battery takes what it needs depending on state of charge, overall size, overall condition etc.

We invented the Combiner in 1994 and have sold nearly 50,000 all on unconditional warranty. Numerous other manufacturers have made copies since then. If this was a problem we would have heard something by now. This has been a "bad" year for returns, we've had about 15. But of those 15, only 5 had anything wrong with them, some purely mechanical, one lightning. An annual failure rate of 0.0125% is why we can give unconditional warranty.

rwthomas1 · Oct 4, 2010

I have an ACR from Blue Seas and love it. Its a model they no longer make but it works as advertised. The alternator and shore power charger are connected to the house bank only. The ACR monitors house bank voltage and closes the relay when it senses a charge from any source, shore or alternator. IIRC, mine also opens the relay if the charge voltage is too high. It has automated the charging process and makes it impossible to forget to switch to "both"

RT

Tom Metzger · Oct 4, 2010

Lots of good info here, but you must remember that the ACR puts current into the start battery that doesn't need it. This lengthens the charge time for the house bank that needs the charge. It will also boil off some water from the start battery.

Keep in mind that the start battery can start your engine at least fifty times on a single charge. Starting the engine typically uses in the range of 1/4 of an amp-hour on an 85 amp-hour battery.

Another negative point with ACRs is that if you normally start the engine with the house bank as most of us do, you will not be able to properly test the start battery. This is because it always has had a recent charge. The correct way to test it is to start the engine after a few days off of a charger.

u079721 · Oct 4, 2010

I installed a West Marine ACR "Battery Combiner" and later decided that it was totally unnecessary for the type of month-long cruises I would take.

I used the big house bank for everything, and just kept the back up battery to start the engine in an emergency. At the dock both banks were kept charged by the Stat Power 40 battery charger, but once underway only the house bank was turned on to see a charge from the alternator. So I got the ACR to keep the back up charged without having to remember to turn it on and off while running the engine. But a couple of tests one year with the ACR disconnected showed that even after a month of cruising the unused and uncharged back up was still fine, waiting for that emergency that never came.

If you are on a mooring and don't have a multi-bank electric battery charger, then this is the perfect solution to keep both banks topped off. Or if you are long term cruising for many months at a time.

But I think for most of us coastal cruising weekenders these things are unnecessary. (IMNSHO......)

Stu Jackson · Oct 4, 2010

One also has to consider where the alternator output is wired.

Most boats come with it to the C post of the 1-2-B switch. Moving it to the house bank is preferable.

Maine Sail and I discussed this here: http://forums.catalina.sailboatowners.com/showthread.php?t=104505&page=2

Please also read the embedded links in that topic, as well as the links within the links fore even more information.

Also http://c34.org/bbs/index.php/topic,4949.0.html

rwthomas1 · Oct 4, 2010

FWIW, I do not use the standard off-1-2-both battery switch. I have the Blue Seas parallel switch with off-on-emergency parallel positions. This switch connects the house bank to house loads and the start battery to the engine independently. The last position allows you to manually combine the two banks in an emergency. The house bank always carries the house loads and the start battery always starts the engine.

I don't buy the unused "emergency" battery school of thought. An unused, infrequently tested battery held in reserve is just as likely to not be up to the task when called upon. Since I use the start battery every time I start the engine I know its condition simply by how fast it turns the engine and how easily the engine starts. I also know that the ACR takes care of charging it automatically.

I am using an Interstate truck starting battery and supposedly it has a slightly different chemistry that is more tolerant of overcharging. Might be a bunch of malarky but it sounded good when I bought it. That said, I have had the Interstate for 4 or 5 years along with the ACR. I have never added water to the Interstate and only had to add water to the house bank 2-3 times in the 5 years I have owned the boat. So my experience has been that the start battery is not being overcharged, it does not adversely affect its lifespan to use an ACR, etc.

The thing you have to realize is not every setup is good for everyone. I like mine, it has not caused my any undue trouble. I've had problems with alternator regulators but thats a different topic.....

RT

Stu Jackson · Oct 5, 2010

Rob's right, there are certainly different ways to do things. The only issue I and others have with the Blue Seas switch is that most unknowing boaters think that using BOTH helps, when it really can hinder things by combining a good bank with bad one. Therefore, the dual circuit switch only has two positions, off and "regular," and not both, which shouldn't be used. I also find our system works by allowing the reserve bank to run very limited house loads if the house bank goes belly up. You just can't do that with the standard wiring arrangement with the dual circuit switch.

I believe in the linked discussions there was talk of testing the reserve bank regularly, and the fact is that many folks have wired their 1-2-B arrangements to have the "start" bank always be used to start the engine. Here's one discussion and wiring diagram to do just that, without having to replace your 1-2-B switch, just adding another single switch and some wiring. It ends up doing just what Rob described without buying the dual circuit switch.

http://www.c34.org/wiki/index.php?title=Catalina_34_Electrical_System_Upgrade

I have the simpleton system and test and use our reserve bank regularly with our Link 2000 and my 1-2-B switch.

Your boat, your choice, no one "right" answer.

The most important thing to do is to get your Alternator Output (AO) off the C post of the 1-2-B switch or whatever switch(es) you may have and run it to the house bank. Prudent application of a circuit breaker or fuse at the house bank is indicated.

Tom is also right. It doesn't really "take charge away from the house bank" 'cuz the battery acceptance limits the charge rate, but overcharging the reserve bank is possible, which is why an echo charger is far superior to a combiner or ACR 'cus the EC is current limiting. That's also why I put a switch on the negative lead of my combiner, which I bought before they invented the echo charger, so I can turn it off when I'm motoring for a long time. I believe Maine Sail discussed this in one of the links I posted earlier in this topic.

tadslc · Oct 5, 2010

I am also going to install the Blue Seas, Off-1-Both switch, for my installation. Understanding the concern of combining a good battery with a bad battery, would it actually drain faster than you could combine and then start the motor? I would think you have a little time before the bad battery effects the good battery. My thinking is once the motor has started, the alternator should start charging the batteries and you can switch back to the 1 position.

Tad

rwthomas1 · Oct 5, 2010

tadslc said:
Understanding the concern of combining a good battery with a bad battery, would it actually drain faster than you could combine and then start the motor? I would think you have a little time before the bad battery effects the good battery. My thinking is once the motor has started, the alternator should start charging the batteries and you can switch back to the 1 position.

Tad

My feelings exactly. Flipping the switch to "combine" is not going to deplete the battery instantly or even in a short period of time. If I was concerned about this then it is a very simple thing to swap the cables from the house to the start battery. Less than 5 minutes in my boat.

RT

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Automatic Charging Relay Question

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