Best Way to Convert 4S Lipo voltage to 13.8v SLA power?

[sikeston34m]

Hi Guys,

I've been researching various ways to convert 4S Lipo Power (16.8v) to 13.8v. 13.8v is typical for 12v sealed lead acid batteries.

Purpose:

I'm tired of replacing the deep cycle sealed lead acid batteries that run the trolling motor in my boat. You might get 2 years out of a regular deep cycle battery.

So 3 years ago, I replaced the tired deep cycle battery with 2 - 6 volt golf kart batteries. They are rated for 5 years of service, but I can already tell, they are getting tired.

Solution:

Build a 4S pack from 18650 cells. (or other cost effective cells)

Problem:

16.8v is not compatible with the system.

I have to come up with a way to step down the voltage to the 13.8v level and maintain this level of amp draw.

My trolling motor is a 12 volt 55lb thrust Minnekota. A general rule of thumb is 1 amp for each pound of thrust.

So, we have to figure on 55 amps at full speed, plus some overhead for comfort.

I've been thinking about paralleling several of the Vicor MegaMod converters for a total of 800 watts of converted power, BUT the units I'm looking at, have an input range of 18 to 36 volts. This would mean a 6S pack would be required to power this unit.

https://docs.google.com/fileview?id=...NTkwYjJm&hl=en

Question: If we are drawing 55 amps from the 13.6v low side, will 55 amps be required on the 6S high voltage side? Probably not, but I still wonder, since voltage conversion is being done with high frequency switching.

Is there a better way to go about this?

I've already checked into 10ah Lifepo4 cells, and just don't like the discharge curve.

By using a DC to DC converter, a steady 13.8 volts can be fed to the motor allowing that fresh, full power feel, all the way to the end of the charge. Thus, improving performance, even over that of a brand new deep cycle SLA battery.

Any ideas? Suggestions?

Let's talk electrical. Feel free to post here guys.

Thanks.