deep cycle batteries 12 volt 24 volt questions

[nmscuba]

Ok, I have searched and read a ton of information here and all over the web about 12 and 24 volt advantages etc. This is going on my 1986 Lund Tyee 16ft

But I still don't really see any real data comparisons such as

1. Since you can use two deep cycle batteries and wire them together for 12 volt you can double your amp hours and get longer run time where with 24 volt you can't do the double part.

2 So taking a Minn Kota 12 volt 55lbs thrust and a Minn Kota 24 volt 55lbs thrust it would seem that you would get a whole lot longer run time on the 12 volt verses the 24 volt even though the 24 runs more efficiently true or false??

3. Batteries. I know the difference between agm, gel, standard and cycles etc. But I see so many people say get optima if you can afford it. But when I look at the RC, Amp Hr etc on the Optima they are substantially less than the other batteries so how is it possible to have longer run times with an optima??

I would of never thought this would be the biggest decision of my boat LOL

So help me break this down. I know the amp draw is about half of the max thrust and all that jazz

 

[UncleWillie]

Re: deep cycle batteries 12 volt 24 volt questions

Comparing Two batteries in Series drawing the same power as Two batteries in parallel...

In Series, the Voltage is Doubled and the Current is Halved compared to Parallel.
In Parallel, the Current is Doubled and the Voltage is Halved compared to Series.

Sounds like No Free Lunch? It is! The power is the same. The run time will be equivalent.

In Series (24v) the current is half so the wiring does not need to be as heavy a gauge. Less money!
Once the Motor goes much above 50lbs your only choice is going to be 24v.

 

[bruceb58]

Re: deep cycle batteries 12 volt 24 volt questions

If you want an AGM battery, don't get the Optima. Get the Oddysey. Sears has the DieHard Platinums which are rebadged Odyssey for less money.

 

[nmscuba]

Re: deep cycle batteries 12 volt 24 volt questions

Comparing Two batteries in Series drawing the same power as Two batteries in parallel...

In Series, the Voltage is Doubled and the Current is Halved compared to Parallel.
In Parallel, the Current is Doubled and the Voltage is Halved compared to Series.

Sounds like No Free Lunch? It is! The power is the same. The run time will be equivalent.

In Series (24v) the current is half so the wiring does not need to be as heavy a gauge. Less money!
Once the Motor goes much above 50lbs your only choice is going to be 24v.

Ok, then, so if the run time is the same and I decided to go with the 24volt 80lbs thrust Minn Kota in stead of the 12 volt 55lbs thrust. The 80 is more than I need but I do get out on rough water and it would be nice to have the extra power if needed.

So with that being said a 55lb draws about 25 amps on full power and if I only ran a 80lb at half power aprox 40 amps then am I correct based on what you told me that I would get the same run time or a little more with this situation?

I really appreciate the info thank you

 

[nmscuba]

Re: deep cycle batteries 12 volt 24 volt questions

If you want an AGM battery, don't get the Optima. Get the Oddysey. Sears has the DieHard Platinums which are rebadged Odyssey for less money.

Im not sure which way im going yet, cause thats another hard decision, lead acid or lot of cycles or Agm for less maint, I have an optima blue top in my plow truck and its the best out there bar none but I didn't think it was the same for marine based on numbers.

I will do some research on the oddessy for sure.

Thank you again everyone

 

[sweet addiction]

Re: deep cycle batteries 12 volt 24 volt questions

This chart might help you. Interstate Batteries

Notice the difference between the Optima vs. say a group 29(SRM29) battery.

 

[bruceb58]

Re: deep cycle batteries 12 volt 24 volt questions

Too bad the chart doesn't share the same specs. For a deep cycle battery, you would want to compare the "Hours at Ampere Load".

At least it has reserve capacity.

An Odyssey 31M has nearly the same specs as a 29 Interstate even though the Interstate is a bigger battery. Way better than the Optima. Not sure why people think so highly of the Optimas. They aren't that great. They used to be OK until the company got bought out and they moved their manufacturing.
http://www.odysseybattery.com/marinespecs.html

 

[Scott Danforth]

Re: deep cycle batteries 12 volt 24 volt questions

If you want an AGM battery, don't get the Optima. Get the Oddysey. Sears has the DieHard Platinums which are rebadged Odyssey for less money.

^^ +1 What he said.

JCI owns Optima and their quality took a dive when they cheapened the product. Oddysey is part of the same battery manufacturing group that supply the military under the Hawker brand name. They are some of the best batteries I have ever had a pleasure to use.

 

[Splat]

Re: deep cycle batteries 12 volt 24 volt questions

Optima batteries are like Bose speakers, high dollar, huge fan base, good marketing. They used to be the cats meow, but quality has suffered in the last few years. If you need a specific mounting requirement for something like needing to mount it on its side under a seat, you may look into them, but if you're looking for quality and capacity, I would look at other brands.

 

[nmscuba]

Re: deep cycle batteries 12 volt 24 volt questions

Too bad the chart doesn't share the same specs. For a deep cycle battery, you would want to compare the "Hours at Ampere Load".

At least it has reserve capacity.

An Odyssey 31M has nearly the same specs as a 29 Interstate even though the Interstate is a bigger battery. Way better than the Optima. Not sure why people think so highly of the Optimas. They aren't that great. They used to be OK until the company got bought out and they moved their manufacturing.
ODYSSEY Batteries - Marine Specifications

The optima blue top in my plow truck I bought last yr and man with the 20 below zero temps we had that 89 dodge cranked up like it was 90 out. But thats a truck.

Now that oddessy 34 is what I liked but omg its over $300 a battery and I would need 2 of them for almost $700 It has a huge RC and such but $$$$$$$ is a lot of cash for weekend fun. I can afford its just I can sure buy a lot of other stuff to restore this boat with the extra I would save.

Its such a hard decision esp if you get the same run time 12 or 24 volts with 2 batteries

 

[bruceb58]

Re: deep cycle batteries 12 volt 24 volt questions

That's why you go buy the Sears DieHard platinum that are over $100 less and the exact same battery.

Comparing the Optima to an Odyssey is apples to oranges.

 

[UncleWillie]

Re: deep cycle batteries 12 volt 24 volt questions

Ok, then, so if the run time is the same and I decided to go with the 24volt 80lbs thrust Minn Kota in stead of the 12 volt 55lbs thrust. The 80 is more than I need but I do get out on rough water and it would be nice to have the extra power if needed.

So with that being said a 55lb draws about 25 amps on full power and if I only ran a 80lb at half power approx 40 amps then am I correct based on what you told me that I would get the same run time or a little more with this situation?

I really appreciate the info thank you

That is correct, at least in theory. Which will be pretty close in this case.


Your numbers seem a little off. Lets assume ~1 Amp per pound at 12volts.
#55 Motor = ~50 Amps at 12v at WOT. 600W
#80 Motor = ~40 Amps at 24v at WOT. 960W

Assuming a typical battery as 12 volts and 100 Ah. or 1200 Watt hour.
Series or Parallel, two batteries would deliver 2400Wh.

The #55 motor drawing 50 amps (Full Power) at 12v or 600 watts will consume 2400Wh in 4 hours. (Each Parallel Battery sees 25A)
The #80 motor drawing 20 amps (Half Power) at 24V or 480 watts will consume 2400Wh in 5 hours. (Each Series Battery sees 20A)
Your results will vary but the principal is sound.

The Battery Amp hour capacity is inversely proportional the the current draw.
The lower the rate of discharge the higher the Ah Capacity.
This favors the 24v Series setup. The reserve power available is always a plus!

Additionally there will be less than half the losses in the cabling due to the lower currents. (20A vs. 50A)
Your power company distributes their power at extremely high voltages at low currents for this same reason.
Consider that 300,000 volts at 3.3 amps is a Million Watts!
With the proper insulation, That could easily be handled by an 18 gauge extension cord!
A Million Watts at 125v would be 8000 Amps; I wouldn't want to have to buy 10 feet of the wire that could carry that!

 

[nmscuba]

Re: deep cycle batteries 12 volt 24 volt questions

That is correct, at least in theory. Which will be pretty close in this case.


Your numbers seem a little off. Lets assume ~1 Amp per pound at 12volts.
#55 Motor = ~50 Amps at 12v at WOT. 600W
#80 Motor = ~40 Amps at 24v at WOT. 960W

Assuming a typical battery as 12 volts and 100 Ah. or 1200 Watt hour.
Series or Parallel, two batteries would deliver 2400Wh.

The #55 motor drawing 50 amps (Full Power) at 12v or 600 watts will consume 2400Wh in 4 hours. (Each Parallel Battery sees 25A)
The #80 motor drawing 20 amps (Half Power) at 24V or 480 watts will consume 2400Wh in 5 hours. (Each Series Battery sees 20A)
Your results will vary but the principal is sound.

The Battery Amp hour capacity is inversely proportional the the current draw.
The lower the rate of discharge the higher the Ah Capacity.
This favors the 24v Series setup. The reserve power available is always a plus!

Additionally there will be less than half the losses in the cabling due to the lower currents. (20A vs. 50A)
Your power company distributes their power at extremely high voltages at low currents for this same reason.
Consider that 300,000 volts at 3.3 amps is a Million Watts!
With the proper insulation, That could easily be handled by an 18 gauge extension cord!
A Million Watts at 125v would be 8000 Amps; I wouldn't want to have to buy 10 feet of the wire that could carry that!

Thank you so much, between your post and the first one explaining this stuff has really made it easy for me to decide to do the 80lb 24 volt. You guys have all been a wealth of information in this forum and I thank you again.

Now to decide on Lead Acid or Agm. Hmmm

 

[nmscuba]

Re: deep cycle batteries 12 volt 24 volt questions

One last question. If I was to get two of these Interstate 4D batteries for a 24 volt Minn Kota 80lb thrust terrova how long would that run if most of my running was around 20lbs or less thrust for average trolling and would it be over kill? I was looking at the 29's then saw these 4D's for under $200 each

Interstate Batteries

 

[UncleWillie]

Re: deep cycle batteries 12 volt 24 volt questions

Every thing you need to know is buried in the Specs you linked.

The 29M shows 3.4h at 25 amps or 85Ah.
The 4D shows 6.5h at 25 amps or 162.5Ah. Essentially Double the Ah and Double the Weight.

Also note just for educational purposes that the 4D show 38h at 5 amps or 190Ah.
The slower you Bleed them the more Blood you Get!

The standard for quoting Ah rating is for a 20 hour discharge rate.
The Amp draw for every battery will be different.

Using our very loose rule of thumb of 1 amp per pound at 12v.
20lbs at 24v would be ~10 amps.
The pair of 29Ms (~95Ah at 10A) would run for ~9.5 hours.
The pair of 4Ds (~180Ah at 10A) would run for ~18 hours.

You would NOT want to routinely run the Batteries much below half, so realistically, figure 5 hours or 10 hours of Continuous running.
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AGM vs Flooded Lead.... Let's open that can of Worms! :facepalm:
This is going to produce some dissenting opinions.

Unless you have a specific reason that requires AGM, Other than Bragging Rights, Flooded Lead Acid cells are the economical choice.

Compare the 27M to the SC34M...
The 34M is Smaller, Lighter, has the same C/MCA Rating but a lower RC.
If weight or size matter, or you need to mount it on its side, Go AGM. Otherwise, Flooded!