Thoughts on 2nd battery and charging relay

[mako172]

I am adding a second battery, switch and an automatic charging relay (ACR) using the Blue Sea 7650 kit. I want to install the ACR after the switch so it is only connected when the switch is on, but the instructions have it directly connected to the positive battery terminals and bypass the switch. Is there a problem connecting the ACR after the switch or should I do as instructed?

Also, what gauge wire should I use from the battery to the switch? The run to my Evinrude 115 is 8 ft each way with 2/0 spliced into 5 ft of 4 guage into the motor.

 

[bowman316]

Re: Help with 2nd battery and charging relay

Re: Help with 2nd battery and charging relay

4 guage should be fine. just nmake sure it is marine grade. I used home depot wire to wire up my sterio, and the positive wire just lost juice after a half year. I think the wire got corroded or wet inside, and was just no good.
I hooked the sterio up to a marine grade wire, and it got juice.

 

[mako172]

Re: Thoughts on 2nd battery and charging relay

I was thinking between 1 and 4 gauge should work. I think I will wire the charging relay with 4 and the battery with 1 gauge.

Here are diagrams of my delema with the charing relay

ACR to Bat

ACR to switch

 

[Texasmark]

Re: Thoughts on 2nd battery and charging relay

Hi Mako,

Trying to help you using logic, not experience because I never did this particular thing before, but I have been close, many times. I made copies of your post and went to the Blue Sea www in an attempt to understand what you have and how (your 7650 kit) it might respond to what you want to do. Going to say what I think is the case and if you know better, tell me.

One of the things that's not clear is if the ACR is a passive sensor (only responds to what it senses from either battery), or if it receives the output of the engine's alternator and distributes it to the batteries. It is probably immaterial in determining what you want to do, butttttt. I say this because there is an upper limit of 16v in the ACR spec. and that could be to protect the batteries if the charging voltage (from the alternator) gets too high. Would like the answer to this.

Otherwise it says that the ACR will just prevent the second battery from getting 16v if it senses it from the first battery; whichever is first and second......, or maybe it has the capacity to open both battery circuits till it's sensor (from a separate sense monitor of the input voltages) senses voltages around 13v.

Assumptions after reading what tech data was available on the www:

1. The ACR has the ability to maintain the voltage on two different batteries to within a narrow range of roughly 13v. If the voltage sensed on either input gets higher or lower it isolates the respective batteries. So, on the down side, if the starting battery starts to feed the engine starter, the ACR will sense the drop on that terminal and isolate the house battery....makes perfect sense.

2. For the ACR to work, it has to sense voltage, and get operational power from, hence be connected to the batteries. If not connected it can't sense, has no power to operate, and thus be useless. With it wired in the lower of your two diagrams (assuming this to be your approach), this is the case and unless you close the switch nothing will happen. But this is ok, because you will not be running the house nor the starter till you turn the battery switch on. It's also ok (probably reason for doing it) because it will not drain your batteries (with it's sustaining current, minor, but none-the-less a battery drain) if left sitting for a long time could run your batteries down....probably your reasoning for wiring as you want to do.

I'd say go for it.
-----------------

Wire sizes you mentioned....size is relative to temperature the insulation is designed to tolerate. If you could keep the temperature of a conductor at 25 degr. C, (through whatever means necessary) you could pump 10,000 amperes through a 20 AWG wire (very small wire if anyone reading didn't know) insulated with any of the plastics, thermoplastics, rubber, Kapton, or whatever insulating material you have available today and not have a problem. Additionally, wire resistance, hence power loss (heat) and voltage drop, depend on controlling that temperature. It's that simple. With a 12v system, you don't have a lot of room (available voltage drop) for resistance to get out of line so you need to watch temperature and what does or does not cause a temperature rise in the wire.

You said you have a 115 hp engine. I have a recent model 90 hp with a factory wiring harness of (pair of...+/-) 6 AWG wires, roughly 6' long for starter power from the battery. I say starter power because as you know the rest of the load could be carried on a 12AWG easily. The engine is spec'd at 125 amperes starting current. Well, the NEC specifies 6 AWG for approximately 50 amperes over 100' or less.....but that is continuous duty, and has temperature and subsequently insulation temperature restrictions/considerations. The duty cycle of your starter is for the most part, instantaneous....in short, your engine starts before the wire has time (heat rise) to know it just passed 150 amperes.

Not real clear where you are going with your 1 AWG and 4 AWG, but if 8' of 4 AWG won't start a 115 engine, time to fix the engine. If you are running your house wiring with 1 AWG, and you need that size wire, I'd like to know what you are using for power because the alternator on your engine can't supply power that heavy and your battery could, but not for long.....so it sounds like real over kill to me. And overkill on wiring is added cost and weight and neither are desired, nor contribute anything to enjoyable boating !!

I think that you will have more problems with interconnection resistance (crimp lugs, terminals, screws, nuts) than with voltage drop along the wiring caused by too small a wire....clean-brite-tight and a little spray coating won't hurt when finished.

I spent a couple hours today trying to help you. I would like a response as I will learn something from this and that is the second half of the reason for trying to help.

Balls in your court and I am interested in your feedback.

Regards,

Mark

 

[mako172]

Re: Thoughts on 2nd battery and charging relay

TX Mark,
Thanks for the detailed analysis. I appreciate the in depth analysis.
As I understand it, the ACR acts as a siphon for the current put out by the alternator while the engine is running. When running, the ACR detects the current and allows the starting battery to charge up to a certain level. When the starting battery reaches a preset level, the ACR starts to siphon current off the alternator and begins charging the house battery. This allows to different battery types (starting and deep cycle) to be charged together but remain independent. If your electronics or trolling motor run down the house battery, the starting battery will remain intact and fully charged since the ACR only works off the alternator current.
The switch operates with 2 input and 2 outputs and when it is ON, input 1 goes to output A and input 2 goes to output B. It maintains 2 separate circuits and only combines the batteries when set to the COMBINE setting.
When connecting the ACR across the positive battery terminals, the voltage loss is minimal and the ACR switches and charges both batteries correctly. My worry is that if I connect the ACR to the switch, the ACR will be less effective since any voltage drop across the switch or wires will cause the ACR to operate less effectively. If I assume that the switch has no voltage loss or resistance, this is not likely an issue and I can do what I proposed.
An added benefit of connecting the ACR to the switch is that the batteries are completely isolated when set to OFF (minus the bilge wich is wired to the house bat). This prevents any charge decay that could be caused by the ACR. It also allows me to independently charge each battery when I return home. I don?t know if the ACR would treat my battery charger like the engine alternator and try to charge both batteries at once. I assume it is best to charge the deep cycle and starting batteries on their respestive settings.
Here is my wiring diagram with my planned cable gauges and lenghts. Once I figure it out I?ll put in the order for the wires. The alternator on my outboatd probably puts out 10-15 amps so I figure 4 gauge for the ACR wires would be sufficient. The battery leads need to carry 100+ amps for cranking so I default to 1 gauge.

 

[trendsetter240]

Re: Thoughts on 2nd battery and charging relay

Hey Mako, I believe your proposed setup will work correctly for all the reasons texasmark outlined.

I don't see any need for 1 gauge wire at any part in the system. 4 gauge will be sufficient for all connections, perhaps even overkill.

With that setup nothing needs to be larger gauge than the wire to your motor. The voltage drop between the batteries and the ACR will be insignificant over 5ft of 4g wire.

 

[Silvertip]

Re: Thoughts on 2nd battery and charging relay

And NEVER turn off the switch with the engine running.

 

[Texasmark]

Re: Thoughts on 2nd battery and charging relay

Not in the order listed:

Man your wire size, for the runs you show and the available volt/amps/time that your batteries can supply, is significantly overkill, especially the 1 AWG. But if that makes you feel good who am I to criticize.

I am going to assume from your response that the alternator is connected to the ACR. Is that true? Things would make a lot more sense if that is so.

On the inputs/outputs of the ACR, probably the inputs are on a separate "signal circuit" within the ACR. It senses what needs to be done with the high current contacts (open-close) and gets it done while "watching" the results. When the desired result is achieved it turns the internal switches off and maintains vigilance on the lines.

I would just have to assume what you said about the ACR was fact in referring to the ACR selectively charging each battery. If the alternator is attached to it as an input then what you say is probably accurate and certainly makes sense for the reasons given; however, the tolerances I saw on the spec sheet for the ACR (low voltage levels and reaction to them) are broad enough that you can probably recharge parallel batteries of different types to within an adequate value to insure 95+% charge. If the ACR monitors charging current to each battery I know this charge condition will at least exist.

Your comments about switch drops and all are well taken and could be a cause for concern if those connections were allowed to deteriorate (corrosion in particular). But I like your idea for locating the ACR where you want to for the other reason we discussed and that to me is reason enough to wire it where you want to.

On the detail, I know it was lengthy, but I can solve problems if I understand the mechanisms involved. Therefore I like to understand how each part of a system works and then I can understand what the system is supposed to be doing, compare that to what it is doing and thereby solve the problem.....so it's time well spent.

Well good luck and happy boating. I have enjoyed the mental exercise. Being retired for 5 years I don't get much of that anymore..............butttttttt that's OK! Grin

Mark

 

[bruceb58]

Re: Thoughts on 2nd battery and charging relay

The ACR should be connected right across the two batteries. There is no need to have it after the switch. The gauge of the wire can be fairly small...6 gauge would be fine. The only time you will have a lot of current flowing is when one battery is very low and the ACR connects in. You will have an inrush of current to the lower battery. This will be actually a higher current than what your alternator will be putting out. This won't last too long so a voltage drop is not a concern. As the current drops , so will the voltage drop. Not sure why Texasmark thinks you will only charge up to 95%. You will get a 100% charge on both batteries...that is why an ACR is so desirable.

 

[Thajeffski]

Re: Thoughts on 2nd battery and charging relay

Hook it up exactly how they say to do it.

I was half drunk when I installed my kit........and i just followed their instructions.....it saved me a few times this summer

 

[bruceb58]

Re: Thoughts on 2nd battery and charging relay

TX Mark,
Thanks for the detailed analysis. I appreciate the in depth analysis.
As I understand it, the ACR acts as a siphon for the current put out by the alternator while the engine is running. When running, the ACR detects the current and allows the starting battery to charge up to a certain level.[/IMG]

That is not how an ACR works. What happens is that there is a voltage detect so that if either battery gets above a set voltage(usually slightly above 13V) the switch will connect the two batteries. The switch is dumb in that it will not be directing any current. basically, the higher battery will flow current to the lower battery until each battery reaches the same voltage. At the same time you are of course flowing current from the alternator into one of your batteries. If the current flow from the alternator is great enough, the higher battery will still stay the same.

A good analogy is two water tanks with a valve and a hose connecting the two at the bottom. The ACR is the valve. If you fill one tank and open the valve, the valve will try to equalize the two tanks and the filling of one tank(your alternator) may or may not keep up with the flow from one tank to the other. Eventually, of course, both tanks will fill completely(charge of both batteries complete).

 

[4JawChuck]

Re: Thoughts on 2nd battery and charging relay

Some observations;

Your wire gauge is way overkill for your 115 HP motor, 6 AWG gauge for the whole thing is plenty. Your motor will have leads coming from it and they will be AWG 6...this is plenty!

Your second diagram now has the ACR before the bats, it must be connected between them to work properly. In your diagram you will be switching power on to the ACR everytime you turn the battery switch on, it draws negligible power to operate and should not be hot switched constantly. In this configuration the ACR will be carrying starting currents which is a big no-no, read the instructions it specifically says not to wire it that way.

In addition you list no fusing components in your diagram, you must use fuses to protect your circuits, review the factory diagram for component layout. The proper layout and fuse locations are on the last page of this document.

http://bluesea.com/files/resources/instructions/990170140.pdf

This is correct;

This is not;

 

[trendsetter240]

Re: Thoughts on 2nd battery and charging relay

Having read through these posts again and spent some time on the Blue Seas site, I don't see any benefit at all for you to place the ACR after the switch. It should be between the two batteries as mentioned.

It will work with your proposed setup but will provide no real improvement.

An added benefit of connecting the ACR to the switch is that the batteries are completely isolated when set to OFF

The ACR will open the switch to isolate the batteries automatically when they drop below 12.75v for 30 seconds.

 

[mako172]

Re: Thoughts on 2nd battery and charging relay

The wire that runs from the console to the back of the boat is as large as my thumb which means it is either 2/0 or 4/0. I was tring to get close without complete overkill. The cost of the wires is fairly low $3.50/ft 1 gauge, $1.50/ft 4 gauge) so the overall difference in cost is minimal for the few feet I want to use the larger wire. Many of the threads I?ve read say use as large as you can afford.

Electrically, any wire connected to the positive wire to the engine is connected to the alternator. The ACR will have one wire connected to the same lead as the engine so it will be able to sense the current from the alternator, though it will be located under the center console.

In terms of charging to full capacity, the old school battery isolators used diodes. Diodes cause a 0.7V drop in voltage by design. When using a standard isolator, the 14.0V being put out by the alternator will be seen as 13.3V by the batteries which means they will nevery be fully charged. The ACR uses more advanced circuitry and does not cause a voltage drop and thus allows the batteries to charge to capacity.

I?m installing a dual battery test switch and upgrading my starter to a 650MCA battery so I can montor their charge while operating. If I have any issues I can move the ACR from the switch to the battery posts in less than a minute. I?ve got a few winter upgrades in progress so the first time out I?ll be followed by a budy in a chase boat.

 

[bruceb58]

Re: Thoughts on 2nd battery and charging relay

The ACR will have one wire connected to the same lead as the engine so it will be able to sense the current from the alternator, though it will be located under the center console.

Apparently you are ignoring all the advice given so far. Just connect the ACR across the battery posts!

The ACR is not sensing current at all. It senses voltage only!

 

[mako172]

Re: Thoughts on 2nd battery and charging relay

My session timed out and my post didn?t go trough as expected. I hit submit again after a few extra counter comments came through. I did more research and it looks like the 15mA drain cause by the ACR will take several years to noticably deplete a battery. This fact coupled with the shock the switch might put on the ACR has caused me rethink my plans.

Seems like most people have had positive experieces with this product (when connected correctly). Anyone had a horror story?

 

[bruceb58]

Re: Thoughts on 2nd battery and charging relay

You should be charging your batteries anyway with some sort of maintenance charger so this shouldn't be an issue. Be aware that if you put a charger on your batteries that the ACR would engage. There is an input to the ACR that you can connect that disables the ACR if you desire. You can also just switch the ground to it to disable it.