Trolling motor batteries and bank charger hookup question

[CobbFisherman]

I currently have 3 batteries in my 1800, one battery that does both outboard cranking and house electronics, and two batteries wired in series to power my 24v trolling motor. I have a 3 bank charger and everything is currently wired like this. Note that the 3 bank charger is hard wired to the batteries with ring terminals, the diagram I used/modified just had the gator clips and I didn't feel like editing that.



I've been doing more and more shallow water trolling and like trolling on the electric motor rather than my E-tec outboard when I'm fishing the skinny water. With my current setup, I can troll for 2-3 hrs on a charge, depending on wind and current. I have group 31 Deka Marine Master batteries, which are about the highest amp hour rating I can find.

If I upgrade to 4 trolling motor batteries, with batteries wired in groups parrallel then connected in series to get 24v with double the amp hours, will my 3 bank charger still be able to charge all of my batteries if I wire it up like this? I think this should work, but with a longer recharge time.




I'm just looking for opinions and input. Thanks!

 

[pelagic2530]

I’m not sure what to tell you on the charger setup, other than that in theory it should work. You’d want to make sure the batteries are the same age and chemistry in order to prevent uneven charging. You also may run into issues with the length of the charge leads not being long enough to reach the terminals of two separate batteries. Either way, you’ll likely be hooking it up in a manner inconsistent with the mfr’s instructions, which may void the warranty or, in an extreme case, cause insurance issues if there’s an issue

My question is, how are you running your TM such that you’re only getting 2-3hrs out of two GP31s?!? I have GP27s and I can run my TM in spot lock for 8+ hours and still have charge to spare. If you’re having capacity issues to that extent, you may be better served with either a lithium battery setup, or by upgrading to a 36v system. Five batteries in an 18 is a lot of space and weight.

 

[CobbFisherman]

I can run Spot Lock under normal conditions for 6+ hrs no problem. Basically, the batteries last all day on Spot Lock.

I'm talking about tolling ~3 mph, which uses WAY more juice than Spot Lock, especially if I'm doing long up-current trolls. I can usually get ~3 hrs of ~3 mph trolling, but I'd like to be able to go longer. Amp hour rating for my Deka Marine Master GP31s is listed at 225 mins @23 amps. My motor pulls about 25 amps at half speed, which is about where it runs for ~3mph trolling. Based on the numbers and calculating for a 75-80% max discharge, my runtime is about right for the battery rating. My batteries are only a year old and I'm getting their rated runtime, so I don't think I have a battery or amp draw issue. Trolling at ~3mph just takes way more juice than Spot Lock.

 

[pelagic2530]

I can run Spot Lock under normal conditions for 6+ hrs no problem. Basically, the batteries last all day on Spot Lock.

I'm talking about tolling ~3 mph, which uses WAY more juice than Spot Lock, especially if I'm doing long up-current trolls. I can usually get ~3 hrs of ~3 mph trolling, but I'd like to be able to go longer. Amp hour rating for my Deka Marine Master GP31s is listed at 225 mins @23 amps. My motor pulls about 25 amps at half speed, which is about where it runs for ~3mph trolling. Based on the numbers and calculating for a 75-80% max discharge, my runtime is about right for the battery rating. My batteries are only a year old and I'm getting their rated runtime, so I don't think I have a battery or amp draw issue. Trolling at ~3mph just takes way more juice than Spot Lock.

Gotcha. That is some seriously heavy AH requirement.

I’ll just reiterate that moving up in available voltage to a 36v motor is likely going to be your best bet. With more power available, your motor won’t be working as hard to make the speed you’re looking for, and your amp draw should be lower. Pair that with a high capacity lithium battery, and I think you’d be very pleased with the result.

If you want to keep your existing setup, I’d still recommend ditching the heavy GP31s and moving to a big 24v lithium setup. You’ll drastically increase your available AH and decrease your weight at the same time, both of which spell a longer run time.

 

[CobbFisherman]

Thanks for the input. Unfortunately, moving up to a 36v trolling motor isn't in the budget. My 24v motor draws about 25 amps/hour running at ~3 mph. Based on the limited data I've seen on the 36v model, it'll probably draw 18-20 amps at that same speed, so that would save ~20% off of the amp load. I'm not sure that's a big enough difference for the $3,000+ cost of a new motor?

I can definitely upgrade my battery setup though. Do you have a recommendation for a lithium battery brand or model?

Because Deka rates their marine deep cycles batteries in a weird way (225 minutes at 23 amps) its a bit hard to compare them to the amp hours that most battery manufacturers advertise, but doing the math these Deka GP31 batteries come out to be about 90 amp hours. So I guess I'm looking for two 12v lithium batteries or one 24v lithium battery with an amp hour rating significantly higher than 90 Ah?

 

[pelagic2530]

Thanks for the input. Unfortunately, moving up to a 36v trolling motor isn't in the budget. My 24v motor draws about 25 amps/hour running at ~3 mph. Based on the limited data I've seen on the 36v model, it'll probably draw 18-20 amps at that same speed, so that would save ~20% off of the amp load. I'm not sure that's a big enough difference for the $3,000+ cost of a new motor?

I can definitely upgrade my battery setup though. Do you have a recommendation for a lithium battery brand or model?

Because Deka rates their marine deep cycles batteries in a weird way (225 minutes at 23 amps) its a bit hard to compare them to the amp hours that most battery manufacturers advertise, but doing the math these Deka GP31 batteries come out to be about 90 amp hours. So I guess I'm looking for two 12v lithium batteries or one 24v lithium battery with an amp hour rating significantly higher than 90 Ah?

I’ll defer to the guys that have installed the lithium systems. But my gut instinct would suggest getting the largest capacity lithium battery that will fit in your available footprint. Not sure what the pros/cons are to two 12v vs a single 24v. But from the sound of it, you can use all the juice you can squeeze into your system.

Be warned: the lithium batteries aren’t cheap either.

 

[knotflying]

When you hook up in series you increase voltage, but not amp capacity. If you hook up parallel you increase amps by the number of amp capacity in the batteries. Hence, with your setup suggestion I would say that you will be only doubling your amperage. On another note. Powerpole makes a wonderful device that manages charging off your engine similar to how your engine battery gets charged while motor is on, but this diverts the charge where needed. Here is a link Power pole link

 

[CobbFisherman]

When you hook up in series you increase voltage, but not amp capacity. If you hook up parallel you increase amps by the number of amp capacity in the batteries. Hence, with your setup suggestion I would say that you will be only doubling your amperage. On another note. Powerpole makes a wonderful device that manages charging off your engine similar to how your engine battery gets charged while motor is on, but this diverts the charge where needed. Here is a link Power pole link

I'll check out the Power Pole charger, thanks.

In my 4 trolling motor battery schematic, I have 2 sets of 2 batteries hooked in parallel, to double the amps, then those two banks of 2 batteries each are connected in series to get 24v. I'm confident that this setup will give me 24v at double my current amps, I'm just not sure if my 3 bank charger or any charger, will accept this configuration to charge?

 

[knotflying]

 

[dave_florence]

Checkout Mastervolt 24V. 24V/25-2 would charge each bank at 24V and 25 amps per 2 battery bank.
I have the 12V/25-3 for 3, 12V batteries, 2 for start, one for house. 25 amps per battery when charging. They can be programed for different types of batteries, but can not mix types.
Mine has a fan, so a little noisey, but a true marine charger.

 

[Dleopoldi914]

What size battery is it? Group 27 or group 31? Where was the last time you load tested the batteries?

i have a 21se and have never run out of batteries, my motor is a 112lb 36v. I’ve left it up to 12 hours spotlocked

 

[CobbFisherman]

They're group 31 batteries. I had the batteries load tested this past March before I splashed the boat for the season. The batteries are in like new condition.

A 36v motor uses ~25% fewer amps/hr than a 24v motor.

I can spot lock all day long on a single charge no problem. My serious battery drain comes from trolling at 3 mph. Spot lock runs the motor as needed at low to moderate speed to hold the boat in place. I need to run the motor at full speed all the time to maintain a trolling speed of 3mph up-river. That's a huge load/amp difference.

I don't think there is anything wrong with my batteries or motor. The batteries load test ok, and I've done the amp consumption and usage calculation and they're lasting as long as the math says they should. The problem is that I'm drawing ~55amps/hour while trolling against or across the current, which I'd like to do for half of the day...

 

[Dleopoldi914]

They're group 31 batteries. I had the batteries load tested this past March before I splashed the boat for the season. The batteries are in like new condition.

A 36v motor uses ~25% fewer amps/hr than a 24v motor.

I can spot lock all day long on a single charge no problem. My serious battery drain comes from trolling at 3 mph. Spot lock runs the motor as needed at low to moderate speed to hold the boat in place. I need to run the motor at full speed all the time to maintain a trolling speed of 3mph up-river. That's a huge load/amp difference.

I don't think there is anything wrong with my batteries or motor. The batteries load test ok, and I've done the amp consumption and usage calculation and they're lasting as long as the math says they should. The problem is that I'm drawing ~55amps/hour while trolling against or across the current, which I'd like to do for half of the day...

It’s advised not to run the motor above 8 for more than an hour

 

[CobbFisherman]

It’s advised not to run the motor above 8 for more than an hour

I guess that's my answer then, I guess the current is just too strong here to troll on my electric motor.

According to the power level / speed/ amp charts I'm seeing online for various trolling motors, it doesn't look like upgrading to a 36v motor would really help me much if I cant run it flat out for hours? Top speed of the 36v and 24v are advertised to be about the same, so if I'm trying to go 3mph and fighting a 2mph current, that's flat out on either motor according to the spec sheet. Or, am i misunderstanding and the 36v motor might go faster at a lower power level?