Blue Sea 7650 Dual Battery Install Question

[84 yota]

Posted this on Ih8mud but posting here as well, as I think there is more action.

Calling all wiring professionals out there.

I am looking to install an aux. battery in my 1987 4Runner to power a fridge for an upcoming trip.

My question is does the Blue Sea 7650 need to be wired as displayed in the diagram in the instructions? The diagram makes sense, but the aux battery would always be connected to the main battery to charge when in the "ON" position. Would it be possible to wire it so the aux. battery is connected to the start battery to charge when in the "ON" position only? Idea is to not always have the aux battery charging. Maybe this defeats the purpose of the system but in my mind it seems like an easier install.

I was googling and found a thread on a boat form with a diagram showing what I am thinking (post#10). https://www.thehulltruth.com/marine-electronics-forum/421319-blue-sea-add-batter-7650-a.html

What do you guys think?

Blue Seas is not open on the weekends for support and I wanted to get ideas before calling them.

I found a thread on here discussion the Blue Sea ACR but it was lengthy and filled with discussion mostly on wiring winches. https://forum.expeditionportal.com/threads/blue-sea-acr-wiring-question.95355/

 

[DiploStrat]

STOP. You are misunderstanding how a voltage sensing/intelligent relay works. The ACR is simply Blue Sea's trade for one of these devices.

An ACR does not read the position of a switch - in operates in response to voltages, thus it does not care if the engine is running or not. The 7650 is simply an ACR with a switch which you can wire to do various things - their diagram shows boat use, but you could use it as a self jump/manual battery combining for winch use, or whatever.

Assuming that you are using two lead acid batteries, a Blue Sea ACR is the gold standard for proper operation. Install it as shown and forget it.

If you are using a lithium iron battery, and you should, especially in a 4Runner or other smaller vehicle, then you will be better off using a battery to battery charger (B2B) from REDARC, Sterling Power, or similar, because of the difference between the voltages of the two batteries.

And remember, a run to battery inside the vehicle should be fused at BOTH ends.

Read the following to understand how a VSR works:

Automatic Charging Relay (ACR) Explained - Blue Sea Systems

Engineering high quality marine electrical components for safety, reliability and performance

www.bluesea.com

 

[DiploStrat]

... Be aware, all ACRs draw some power to operate. This one draws 15mA when open.
While not much, it adds up. If you dont drive the car much, you should install its optional disable switch.

True, but given that I have around 5A of background noise, I couldn't see 15mA if I tried!

But I am talking about a much bigger system.

I agree with your point about the switch; probably not needed for a small system. I tend to like the option of a master kill switch to isolate the camper battery for installation, etc.

To me the real issue is lead vs. lithium. In any system, but especially a smaller on, e.g. 200 Ah or smaller where weight can be a real issue, lithium is a better way to go and a B2B comes much closer to providing a proper charge.

 

[84 yota]

Appreciate the replies!

I posted on here last night when I was tired and didn't give the full story.

Reading more about the Blue Sea diagram last night, my thoughts were the same that it is wired for a boat and in the "OFF" position cuts power to the whole system. This is not what I want.

I have the factory lead acid start battery and a Renogy 100Ah deep cycle lead acid AGM battery. https://www.renogy.com/support/down...e-agm-battery-w-battery-box-rbt100agm12b.html

What I want:

1. Place aux. battery in rear of vehicle
2. Hook up fridge to aux battery
3. Automatically charge aux. battery
4. Be able to disconnect aux. battery from charging circuit if I want to remove battery

My question is, can I wire the system as I drew on cardboard? I understand I need to add fuses too, 100Amp at each end of the batteries.

 

[DiploStrat]

Again, you are not understanding how the ACR works. Ignore the switch for the moment; you don't need it.

Basically, you run one wire, fused and of the correct gauge for the distance, from the positive terminal of the starter battery to a terminal on the ACR. You run another wire, fused and the same gauge, from the positive terminal of the camper battery to the other terminal on the ACR. (The ACR may have a ground as well.) That's it.

Read through this: https://cookfb.files.wordpress.com/2016/09/dual-battery-slides-2016.pdf
You can add cut off or combine switches to your heart's content. Or you can buy ACR's that have a dashboard override switch and tell tale. But basically, an ACR is install and forget.

Now, all of that said, I would not recommend an ACR today, especially not in an older Toyota.

-- Older Toyotas are notorious for charging at 13.9v. Fine for a starter battery, but the kiss of death for a lead acid camper battery which will need to get to 14v+.

-- Lead may not be dead, but it is an outdated technology for a camper battery. You will be going to lithium iron eventually.

-- Build your system with a battery to battery charger today (for small systems like yours, the REDARC BCDC 1240D or 1250 is really easy. Sterling and others have other options as well.) and you will probably get more life out of your lead acid battery and be set up for a lithium iron when you get tired of lugging twice the weight for half the output.

 

[DiploStrat]

Some final notes:

-- The slide deck on dual batteries is a bit dated. Why? Because everybody has gone to lithium iron and I have been too busy to update it.

-- This is the presentation you want to read: https://cookfb.files.wordpress.com/2022/10/move-to-lifepo4-2022.pdf

 

[fratermus]

I would not recommend an ACR today...
-- Build your system with a battery to battery charger

I value your input on this thread.

If the recommendation against ACR/VSR is particular to OP's stated use case then I agree. If it is a deprecation of relays in general then I will push back.

In situations where solar is present the solar charge controller will be providing the proper Absorption voltage for lead chemistries. DC-DC may be needless expense. I've fleshed out the idea in this article.

You will be going to lithium iron eventually.

The Toy's 13.9v would be about perfect for direct-charging LiFePO4, gentle on the chemistry and reducing current (I=V/R).

 

[84 yota]

Thanks for the replies and links.

I will measure the alternator output on the 4Runner.

I also understand that a lead acid battery is older tech and not as good as a lithium battery.

That said, I have the AGM lead acid and Blue Sea ACR in my hands, and that is why I wanted to use them.

I am leaving on a trip next Saturday the 15th. What would you recommend?
I am not going to leave this system in long term because I do not want to modify this 4Runner. I simply want to install this camper battery just for the fridge for this trip.

 

[fratermus]

I have the AGM lead acid and Blue Sea ACR in my hands, and that is why I wanted to use them.

I am a big fan of working with what one already has.

The main challenge in this situation is lead wants to be 100% state of charge all the time.* In practice we limit damage by keeping it 100% SoC as much as possible. Adding solar is the usual approach but I understand that's not happening with this build.

For a weekending/recreational setup without solar we can limit damage to the AGM by keeping it on a shore power charger when not in use (plug in the vehicle when you get home). It can be a small (10A) charger as long as it has an AGM profile that meets the battery manufacturer specs. A quick-connect will make connection painless. A nice side effect is the ACR will see the increased voltage during charging so your starter battery will also be maintained. Win-win.

-----

* Lithium does not need (or even want) to be 100% SoC all the time, which is one of the reasons it works well in this kind of use case

 

[DiploStrat]

Thanks for the replies and links.

I will measure the alternator output on the 4Runner.

I also understand that a lead acid battery is older tech and not as good as a lithium battery.

That said, I have the AGM lead acid and Blue Sea ACR in my hands, and that is why I wanted to use them.

I am leaving on a trip next Saturday the 15th. What would you recommend?
I am not going to leave this system in long term because I do not want to modify this 4Runner. I simply want to install this camper battery just for the fridge for this trip.

The ACR is an excellent bit of kit. With the caveats about the switch, install it and use it; it should do exactly what it says. I used a home brew VSR for years when I had AGM batteries.

With a lead acid camper battery, the only challenge is getting a high enough voltage to charge quickly and completely.

Options to complete the charge include a solar charge system with the proper, higher voltages and/or a weekly, bi-weekly, or at least monthly session with a good shore charger that can complete the charge.

A bit old, but this discusses the challenges of keeping lead acid batteries happy. https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf

 

[84 yota]

Ok thanks.

Just so I understand this correctly, my plan is:

1. Do not use switch?
2. Leave factory starting wiring
3. Run wire with fuse from start battery to ACR
4. Run another wire fused from ACR to second battery
5. Run ground from 2nd battery back to start battery ground
6. Use more powerful charger when back from week long trip to properly charge 2nd battery to appropriate level

Sound good?

 

[DiploStrat]

Ok thanks.

Just so I understand this correctly, my plan is:

1. Do not use switch?
2. Leave factory starting wiring
3. Run wire with fuse from start battery to ACR
4. Run another wire fused from ACR to second battery
5. Run ground from 2nd battery back to start battery ground
6. Use more powerful charger when back from week long trip to properly charge 2nd battery to appropriate level

Sound good?

I think you have it. You may want to review this: https://cookfb.files.wordpress.com/2016/09/dual-battery-slides-2016.pdf

1. Use switch or not for any purposes that you may want, e.g., kill switch for the second battery, force combine for winching or self jump, etc.

2. Leave factory wiring untouched.

3. Run a fused wire from positive terminal of start battery to ACR, fused at the start battery end. Blue Sea makes a "Terminal Post Fuse" that makes this easy. Size wire appropriately for load. (At least one of my slide decks has a chart.)

4. Run similarly sized wire to second battery, again fused at the battery end.

5. Properly/securely install second battery and ground. Usually the same frame rail as the start battery.

6. Read the charging specs for your second battery and use a shore charger that can do a proper absorb charge when you can. After every trip is great. Absorb voltage and time are critical to good AGM battery life.

7. Most essential step, have a great trip! (And hope I didn't miss anything! )

 

[84 yota]

I am months late to reply, but I wanted to follow up and show how I wired it. Thank you @fratermus @DiploStrat. I really appreciate it!

System worked great for the week long camping trip to run the fridge.

I understand the system is not the most ideal setup, but worked well for this application.

 

[DiploStrat]

Glad I could help, if only a little.

Wiring looks better than mine. Don't know the switch logic, but I assume it allows you a force combine.

As noted, with AGM, the BIG thing is that long absorb stage @ 14.Xv. The suggestion of a small, but proper, shore charger is excellent, especially as the ACR will close once the voltage rises above 13.2v (or so) and thus the charger will maintain your starter battery as well.

Have some great trips