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Wiring 12V Batt In Parallel Vs Keeping Spare On Board.

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I've read through several of the older threads here about wiring trolling motor batteries in parallel which obviously increases run time although I can't seem to find an answer to my question.

When running off 1 battery and keeping the 2nd battery on board as a spare will it give me more, less, or the same amount of run time as running the two batteries in parallel?

I have a 16' fiberglass bass boat w/ a 36lb trolling motor which I do know is pretty underpowered for my boat but it gets the job done on the electric only lakes I fish. However, on windy days when I'm on the motor very often I find myself running my battery down within 3 hours.

I just purchased a 2nd identicle deep cycle battery and have been using it as a spare but am considering wiring it in parallel with my other if it will increase my runtime overall. I also plan on upgrading to a 55lb thrust and was wondering if the larger motor will run my batteries down quicker than my current 36lb. I would like to go to a 24v motor but the lack of storage in my older boat wouldn't allow me to wire 2 24volt banks in parallel and I fear I will run a 24 volt motor down to quickly with one set of batteries.

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The deal is if you just use one battery at a time, you can have a fresh unused battery as a backup when the first one is depleted.

If you run both of them down equally, you could be using your paddle.

FYI, I see it a lot where someone leaves the ramp with an electric motor at the highest speed setting and "runs" to a location to fish. That kills the battery faster than any other way you can use it.

Yes, the 55# 12V motor will run the battery down a lot faster than your 36# motor if you run it on the highest speed setting. It takes amperage to get the higher thrust (it ain't free).

A 24V motor with two batteries in series will have more power at about 1/2 the speed setting and get the same performance as your 36# motor at the highest speed setting, That in itself will give you about twice the run time.

You won't need tandem 12V batteries for a 24V motor. You won't find a deep cycle 24V battery that you can use in your boat.

The next best option is a 55# thrust motor 12V that has a variable speed control and do not run it at the fastest speed setting. The electronics of a variable speed motor uses less power than a selectable speed motor at the same speed. The variable speed circuit is not in use at the top speed setting. Take advantage of the pulse modulation those motors have.

FInally use batteries that have the most amp hours or reserve capacity to get the longest run time. A group 27 is a good compromize, but a group 31 is better. Never get a group 24 for trolling motor use.

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The deal is if you just use one battery at a time, you can have a fresh unused battery as a backup when the first one is depleted.

If you run both of them down equally, you could be using your paddle.

FYI, I see it a lot where someone leaves the ramp with an electric motor at the highest speed setting and "runs" to a location to fish. That kills the battery faster than any other way you can use it.

Yes, the 55# 12V motor will run the battery down a lot faster than your 36# motor if you run it on the highest speed setting. It takes amperage to get the higher thrust (it ain't free).

A 24V motor with two batteries in series will have more power at about 1/2 the speed setting and get the same performance as your 36# motor at the highest speed setting, That in itself will give you about twice the run time.

You won't need tandem 12V batteries for a 24V motor. You won't find a deep cycle 24V battery that you can use in your boat.

The next best option is a 55# thrust motor 12V that has a variable speed control and do not run it at the fastest speed setting. The electronics of a variable speed motor uses less power than a selectable speed motor at the same speed. The variable speed circuit is not in use at the top speed setting. Take advantage of the pulse modulation those motors have.

FInally use batteries that have the most amp hours or reserve capacity to get the longest run time. A group 27 is a good compromize, but a group 31 is better. Never get a group 24 for trolling motor use.

Thank you so much for the info. I currently have 2 group 27 Everstart deep cycles. I do run my 36lb motor at the highest selectable speed setting due to it being underpowered for my boat which im sure is why my run time is so limited on windy days.

I understand what your saying about having the spare for when my first one runs down to switch to a fresh 2nd one and that if I have them in parallel and run them both down equally I will paddleing but that doesnt answer my main question. Will I get more, less or equal run time running them in parallel vs seperate and switching?

I don't understand what you mean when you said:

"You won't need tandem 12V batteries for a 24V motor. You won't find a deep cycle 24V battery that you can use in your boat."

Don't I need two 12V batteries wired in series to run a 24V motor? I know I wont find a single 24V battery that I can use. Are you just saying I wont ever need more than the 2 batteries wired in series to last me all day long w/ a 24V motor? My concern was with 2 batteries wired in series if I run them down on a 24V motor I will be paddleing with no upgrade options. I don't have the storage room for 2 additional batteries to create a 2nd 24V setup to wire in parallel with the first or run seperately when the first runs down.

With that being said, it seems like my best option may be to upgrade to a 70lb thrust 24V. I will get the same speed or better than my 36lb because I wont need to run it near it's fastest speed to achieve the equivalent speed of my 36lb at it's fastest. This should roughly double my run time which will equal out to about the run time I get now keeping a 2nd 12V on board for my 36lb.

A 55lb will give me greater top speed but deplete my batteries even faster than my 36lb and running the 55lb at a slower speed maybe equal to the 36lb top speed to increase run time kind of defeats the purpose in that upgrade all together.

I am unfamiliar with the variable speed motors. How do they work, is it by the pressure you put on the pedal to increase speed much like the gas pedal of a car? Again thank you for helping me out with the above info. If my thoughts are right do you think a 70lb thrust 24V would 100% be the best option for achieveing maximum performance and run time with my limited battery storage space?

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Well, you explain this: "I would like to go to a 24v motor but the lack of storage in my older boat wouldn't allow me to wire 2 24volt banks in parallel " .

A foot controlled 3 or 5-speed motor has a knob that selects the different speeds by turning it to each speed selection.

A variable speed motor has the same type of knob to adjust the speed, but there are no spaces between the speeds--it is a gradual adjustment. Between the lowest and almost the highest speed setting, there is an electronic circuit that pulses the voltage so there is not a continuous current draw. That uses less battery power.

It is sort of like the turn signal flasher on a vehicle--just faster pulsing.

Yes, the 70# 24V is your best choice, even more so if is a variable speed model.

Still you will run that motor at a lower speed setting than the 36# model when you are fishing.

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Well, you explain this: "I would like to go to a 24v motor but the lack of storage in my older boat wouldn't allow me to wire 2 24volt banks in parallel " .

A foot controlled 3 or 5-speed motor has a knob that selects the different speeds by turning it to each speed selection.

A variable speed motor has the same type of knob to adjust the speed, but there are no spaces between the speeds--it is a gradual adjustment. Between the lowest and almost the highest speed setting, there is an electronic circuit that pulses the voltage so there is not a continuous current draw. That uses less battery power.

It is sort of like the turn signal flasher on a vehicle--just faster pulsing.

Yes, the 70# 24V is your best choice, even more so if is a variable speed model.

Still you will run that motor at a lower speed setting than the 36# model when you are fishing.

Thank you again, a 70# 24V variable speed it shall be for me :)

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Run them in parallel.

Yes, running them in parallel does increase run time, rather significantly if draw a lot of amps. The typical rating for a deep cycle battery is in Amp Hours and they normally use the 20 hour standard. This means they apply a small load to the battery, enough to discharge the battery in 20 hours. If takes a 5 amp load, then it's a 100 amp hour battery. If it takes a 6 amp load, then it's rated as a 120 amp hour battery.

Now, in the real world of fishing an running TM's there is going to be a whole lot more load then five or six amps. As you increase the load, the amp hour capacity goes down. The heavier the load, the more the amp hour rating is reduced. To the point your 120 amp hour battery may only be a 75 amp hour battery under a heavy load. So, if you have the batteries in parallel, that cuts the load in half because it's divided between two batteries, therefore, increasing the amp hour capacity

That's why the reserve minute rating is a better indication of how much runtime you can expect over Ah capacity. Resever minutes is normally based on a 25 amp load, which is much closer to what you will be pulling with your TM in a more usuable speed. The reserve minute rating is how many minutes a good battery will run with a 25 amp load. Some batteries cheat with that also and only use a 20 amp load to make their numbers look better, so check and see what load they are using for their rating so you can compare apples to apples when check out batteries.

Just like in the Ah capacity though, if you increase that load from 25 amps to 50 amps, the reserve capacity is going down, again why it's best to run them in parallel to cut the current draw down.

Yea, you can run one until in dies, in a couple of hours if running in medium speed and swap an run the other a couple of hours until it dies, or you can run them in parallel and run the two of the for six or seven hours.

Now as for your last comment. You will not be running 24 volt batteries to worry about having them in parallel. The typical 24V installation is with two 12 volt batteries in series. If you find 24 volt batteries, they are going to be very expensive and normally too big.

The advantage a 24 volt system gives over a 12 volt system is it's about 25% more efficient. Meaning it runs 25% longer on the same battery capacity as a 12 volt motor.

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