24 volt charging help

[huntncoug]

I have a Minn Kota 72 thrust dual battery setup. What is the best charger to use and the best method?

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I have a Minn Kota 72 thrust dual battery setup. What is the best charger to use and the best method?

I assume you are using two 12volt batteries “daisy chained” together to make a 24volt battery. If this is the case and you own a 12volt charger I would reverse the wiring between the two batteries and charge both of them simultaneously with your charger set on 12volts.. Of course, you can always spend the extra money and get a 24volt charger.

[huntncoug]

Yes I am using two twelve volt batteries with a 12 volt charger. I have been disconnecting them and charging them individually. I didnt know I could reverse the wiring and do them together, that sounds like a good idea, this sounds stupid but how do I reverse them?

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Yes I am using two twelve volt batteries with a 12 volt charger. I have been disconnecting them and charging them individually. I didnt know I could reverse the wiring and do them together, that sounds like a good idea, this sounds stupid but how do I reverse them?

Right now your batteries are connected positive to negative. Just connect them positive-to-positive and negative-to-negative. By doing so you have changed the voltage back to 12 volts.

[Anglinarcher]

Huntncoug, I have just gone through this, and there are several ways to do this, some easier and cheaper than others.

First, if your MinnKota has the Universal Sonar (US) attachment, like mine does, than you should be using three batteries on your boat. You should have a cranking battery, than the two 12 V batteries hooked in series. If you don't have the US, than you can use just two batteries, hooked in series, but I warn against this. I have been caught out in the middle of the Netherlands when I discovered I had forgotten to turn off my live well and my cranking battery was dead. It was nice to at least have the ability to relocate the other battery to start the big engine. I have seen boats that had the trolling and cranking batteries hooked in series where the trolling motor ran the batteries down, and I ended up towing the dude back to the closest dock (I will charge for gas next time).

Now about charging; you do not need to unhook your batteries to charge them individually. You can just hook the charger directly to the positive and negative terminal of a single battery and then change the charger over to the other battery when the first is done. The current flows through a closed loop/path, and the other battery is not impacted at all by doing this. You do not need to disconnect your batteries from the rest of the system; remove the charger when you are done and go fishing. This of course is the cheapest, but it is the slowest.

You can do as stampie has advised, but make sure you disconnect the batteries from the rest of the wiring. By taking the batteries back to the 12 volt system (you have hooked them in parallel instead of series), if you forget and try to run your motor without changing them back you can damage it. In other words, 24 V motors overheat if you try to run them on 12 V. It takes time to make the battery terminal changes, and you will find there are other problems as well.

If you are using lead acid, full maintenance batteries, than consider the batteries throw-a-ways after one, maybe two years. You will benefit little from using a quality charger. If, on the other hand, you are using Absorbed Glass Matt (AGM) or Gel Cell batteries, maintenance free, you should be using a three stage charger. The battery life is extended, the charge cycle is improved, and you will get FULL performance from your batteries for many years. I have two that are going on 5 years now, and each has been run to death. I just upgraded my motor to a 24 V system, and I do not plan on changing out the Gel Cell that I have been using; it is in that good a shape. BUT, if you use a three stage charger, doing as stampie has suggested fools the sensors in the three stage charger into think that the battery is not fully charged yet, keeping it in the bulk charge mode longer, keeping it in the top off mode less, and leaving higher than desired current in the maintain mode. This will shorten the life of your batteries.

Stampie's method can work, and can be cheep if you are using Lead-Acid batteries, but it is also the hardest because you are always changing the batteries cables.

The most expensive, but the most reliable, the fastest, and the best for your batteries in general, is to install an onboard charger. Assuming you want to charge your cranking battery, and the two trolling motor batteries, you want a 3-bank on board charger. I got a good 3-bank, three stage, onboard charger from Cabelas for about a $180 bucks. Because of the location I mounted it, I needed to spend about $20 to get a cable extender set to reach the cranking battery.

It was not all that hard to run the cables, and each set of cables hooks directly to a single battery. The batteries are left connected to the system. The cranking set is labeled for the cranking battery; the trolling battery cables are also labeled. I did some fancy wiring to enable me to secure the plug of the charger in a recessed/waterproof plug cover. Now when I get home, I open the cover, pull out the 110 V plug, plug it in, and walk away. I can leave it plugged in forever and it will monitor the batteries and keep them maintained. This is critical for over-winter storage, or even long term storage.

When you consider the cost of a good AGM battery, $180+, or a good Gel Ceil, $220+, than the cost of the onboard charger is easily offset by the added battery life and ease of charging.

An additional comment if you please. You can save a bit of money by just getting a 2-bank system and not charging your cranking battery with the onboard charger. Your motor does have a charger, but you loose about 2% charge on a battery per month in storage during the summer, even more during the winter. You will need to do something during storage on the cranking battery, and you will not get the life out of your cranking battery you would like.

And my final comment; all batteries should be the same type (Lead-Acid and/or AGM, or Gel Cell - AGM and Lead-Acid are OK if combined) when hooked up to an onboard charger. If you have mixed batteries, set the charger to look for Gel Cell, even if you have one battery that is not a Gel. Still, it is recommended that you do not combine a Gel Cell with the other two types for best charging.

[danielt]

Id just get a dual bank on-board charger. I only need to charge my cracking battery once every 4 months but keep jumper cables on the boat in case it does die.

[ChrisB]

Daniel is right, easiest route is to buy a dual bank charger and just plug it in and forget about it. I use 3 batteries (2 deepcycle and 1 starting), and I have a 3 bank charger for my boat.

[Anglinarcher]

Id just get a dual bank on-board charger. I only need to charge my cracking battery once every 4 months but keep jumper cables on the boat in case it does die.

This works, but you are shortening the life of your cranking battery by leaving it at less then full charge.

Nevertheless, I have done it myself.