Charging a 24V Battery System

[Reinhardtius]

Hi Folks,

I am installing a Noco G7200 battery charger/maintainer to my BJ75. The eyelets are too short to run from both batteries, and it probably would be a wiring mess, too. The people on the phone and the manual says I can mount one eyelet to the + on the positive side (driver side, left hand drive) and then just mount the - eyelet to some part of the chassis, rather than going all the way over to the other battery - on the passenger side.


Are they right, and can I mount the - eyelet to the bolt where my arrow points? Sorry to be an air-head. I don't want to fry anything.

 

[augirthedude]

Just make sure the positive post you attach the positive lead to reads 24 volts to Ground with a volt meter . The other battery positive post will read 12 volts to Ground. If it is 24volt system the batteries will be wired in series.

 

[Reinhardtius]

Just make sure the positive post you attach the positive lead to reads 24 volts to Ground with a volt meter . The other battery positive post will read 12 volts to Ground. If it is 24volt system the batteries will be wired in series.

Thanks. Confirmed that they do. Charging now and I’m getting a reading on my multimeter of around 28.5 volts

 

[augirthedude]

I too have started using Noco products chargers on my standby engines for the ski lifts in my care as well as at home.

 

[Reinhardtius]

I too have started using Noco products chargers on my standby engines for the ski lifts in my care as well as at home.

So far so good? Can I feel at ease about leaving the truck plugged in?

 

[augirthedude]

Yep I leave them on 24/7 . My applications are 12volt. So far so good with the 3.5 amp model.

 

[Freewheel]

That will work, but if you want to guarantee that the batteries get charged equally, you may want to get the 4 lead 12 volt system and charge each of the batteries separately (I use the NOCO GEN 2 Mini for this) You don't have to disconnect the truck wiring, but you can't use frame ground for the high side negative.

The 7200 will charge 24 volts nicely, but if there is a battery imbalance it won't correct it. You need to charge each battery at 12 volts to do the balance. The other way to balance would be to occasionally use the the 7200 in 12 volt mode charging one battery then the other.

This is nit picky stuff, and may be overthinking it- but I generally get very good life out of my batteries being picky about keeping them balanced.

 

[FordPrefect]

I agree,
I use 2 x seperate 12v smart chargers (one per battery). To maintain our 24v HJ.
I have found that charging 24 volt at the same time does not bring up both batteries to exactly the same full point.
If you connect separate voltmeters to each battery and observe, even when driving daily, both batteries can have slight charge differences.

 

[augirthedude]

That will work, but if you want to guarantee that the batteries get charged equally, you may want to get the 4 lead 12 volt system and charge each of the batteries separately (I use the NOCO GEN 2 Mini for this) You don't have to disconnect the truck wiring, but you can't use frame ground for the high side negative.

The 7200 will charge 24 volts nicely, but if there is a battery imbalance it won't correct it. You need to charge each battery at 12 volts to do the balance. The other way to balance would be to occasionally use the the 7200 in 12 volt mode charging one battery then the other.

This is nit picky stuff, and may be overthinking it- but I generally get very good life out of my batteries being picky about keeping them balanced.

No two batteries have the exact characteristics.. one will always be lagging behind the other. Especially if you have a 12 volt center load tap for any 12 volt accessories. I’ve fought this issue for years back in the old days with ski lift control system which are usually 24 vdc . I’ve had the best results using 2 , 12 volt chargers as well.

 

[george_tlc]

Agree that the best option (well, the best is if you can ditch the 24V system completely...) is 2 independent 12V chargers, one per battery. That's really the only way to get both batteries fully charged and maintained.

And obviously you NEVER want to run a 12V accessory from a single battery in a 24V system.

Best thing ever was converting my 24V patrol to 12V

cheers,
george.

 

[TrailRunner40]

I’ve got a newbie question for y’all...

I’m new to 24v and have been charging my batteries independently by taking off the cables before charging. Is it necessary to remove the cables or can I go directly to the + and - battery posts while they are tied?

 

[george_tlc]

^ you can charge with the batteries in vehicle and connected normally.

The ONLY thing to be careful with is the 'case' of the charger (IF it is a metal case) - i.e. if the case is grounded to the negative 'output' of the charger, then you don't want the case to touch the body of the vehicle when charging the high 12V battery.

cheers,
george.

 

[Reinhardtius]

That will work, but if you want to guarantee that the batteries get charged equally, you may want to get the 4 lead 12 volt system and charge each of the batteries separately (I use the NOCO GEN 2 Mini for this) You don't have to disconnect the truck wiring, but you can't use frame ground for the high side negative.

@george_tlc that sounds like a better solution.

To use the Gen 2 Mini, would you set it up like this?:
1. For the driver side battery, you mount bank 1 charger eyelets to the + and - of the battery (no frame ground).
2. And, for the passenger side battery, you mount bank 2 charger eyelets to the + and - of the battery (again, no frame ground).

And also, just confirming that I can leave both batteries connected to the vehicle's electrical system while charging? I would have thought that 12v coming in from each charger could create a problem. But then again, I don't know much about this at all.

Thanks for entertaining my ignorance,

Reinhardtius

 

[george_tlc]

^ yes, what you have described in 1. and 2. is correct and safe.

Yes, you can leave the two batteries in vehicle and connected normally. The chargers won't cause any issues to the electrical system. Just remember to disconnect power cords before you drive off

cheers,
george.

 

[Freewheel]

And I'll confirm that's exactly how mine is set up.

 

[Greg_B]

I've got two of the Noco 7200 and one Noco Gen2 mini. I've used the 7200's to maintenance charge the BJ42 and BJ74 when not being used. I was concerned about any battery difference being exacerbated over time, as happens with alternator charging. My experience has been that for medium term storage (two months plus) any imbalance has stayed the same or the batteries have come closer together. If that is due to the smart chargers programming or not, I do not know.

I've had one experience with charging two 12V batteries in series since purchasing the 7200's that was interesting. I had purchased two Canada Proof dual purpose 27 series batteries when my BJ74 batteries failed. I ran them for a number of months, then put the 7200 on the batteries when I was not going to use the BJ74 for a while. Within three days the 7200 shut off. I switched to the other 7200 and the same thing happened. The batteries resting voltage were different (don't recall how different), but they individually load tested fine. I took the batteries out and put them on the Gen2 Mini to see what would happen (thinking perhaps a warranty claim). One battery went to green light within a day and other other battery took a number of days to get a green light. (When the green light is on the programming is still working to get the battery to 100% and into maintenance mode. Checking with a voltmeter will tell you if it's desulfation or in maintenance/float). I left the batteries hooked up to the Gen2 mini for a while so the smart charger would run its programming. When I put the batteries back into the truck (BJ42 this time) the 7200 happily charges then goes into maintenance mode.

I take from that experience that the batteries (even though same brand, series and purchase date) were far enough apart in capacity that the 7200 would sense a problem and shut off. Once they were treated individually they are now close enough the 7200 works fine in 24V mode charging.

My take-away is:

If I was in the market to buy a charger for a 24V system I would now be inclined to go with something like the Noco Gen2 Mini.

As I have the 7200's I will continue to use them in 24V mode for my charging needs on the BJ74 and BJ42 as needed, (and they are good 12V chargers) but agree with the above; No two batteries are completely alike so charging them individually is best.

hth's
gb

EDIT Feb 2024: In the theme of evolution though use, I have modified my thoughts above due to the Noco not being able to act as a charger/maintainer and power supply from this experience. I now have a 24V Victron charger on board full time as explained in the linked posts. Also just got a 12V Victron for use with the 80 series, which has two 27 series DP batteries in series. Again, to address the same issue (Not being able to maintain a cycling load like a fridge, while also looking after the batteries).

I will continue to have and use (on occation) the Noco two bank charger, to ensure each battery is at 100%, when either vehicle is in storage and the fridge is off.

hth's
gb

 

[Reinhardtius]

Extremely helpful reply. Thank you @Greg_B

 

[Reinhardtius]

Well, I returned my G7200 today and await the Gen 2 Mini. I'll post photos of the install.

@Greg_B and @Freewheel can you please show us a photo of how you've got your Gen 2 Mini's configured?

 

[bj70_guy]

Well, I returned my G7200 today and await the Gen 2 Mini. I'll post photos of the install.

@Greg_B and @Freewheel can you please show us a photo of how you've got your Gen 2 Mini's configured?

Greg's Mini isn't installed in a truck, he just uses it on the bench in his shop - at the moment at least.

FWIW this is the install in my HDJ81. It was already done when I bought the truck. Just a simple piece of bent aluminum bolted to the inner fender. It's a 12V truck but setup would be the same for a 24V truck, each battery wired separately.

Its awfully nice having it on board.... I suppose I should really get another for my BJ74.

 

[Freewheel]

Mine's not mounted permanently yet. But it sits pretty nicely between the overflow bottle and and the fender. I've got marine batteries so it's wired with ring connectors to the threaded auxiliary posts.