Will 18 volts damage a 12 volt trolling motor?

[bigriver]

Probably a no brainer question for somebody. Looking at using
dewalt 18 volt lithium ion batteries to power a 12 volt trolling motor
on a kayak. Will this damage the motor? If so what is the best method
to step the voltage down 12 volt?

Thanks

 

[loquin]

It may well damage the motor - or more precisely, the motor controller... (the motor itself would probably handle the overvoltage just fine)

The most efficient method would be to add a switching regulator between the batter and the motor. A switching regulator works by switching the 18 volts on and off rapidly, adjusting the on time to off time ratio so that the average output voltage would be 12 volts. This switched voltage is fed through an internal filter on the regulator output circuitry, which 'averages' the output voltage to the load.

You could use a big resistor, but, the voltage drop across the resistor is wasted power. And, as the battery voltage drops, the motor voltage drops proportionally.

A linear regulator doesn't have the output voltage drop issue, but, it wastes just as much power as the resistor. (at least 1/3 of the total available power is wasted in the resistor/linear regulator approach)

However, the Dewalt tool batteries may not have the capacity to keep your trolling motor going for very long...

 

[bigriver]

Any quick links for someone that sales switching regulator or does this have to be built?

 

[loquin]

search for High Efficiency DC-DC converter

or, use 12V batteries (which would certainly be simpler...)

 

[bigriver]

thanks. Yea considered the 12 volts just already have 18 volt tools and was thinking "double duty". May just run at 18 volts and see what happens, i.e. damage, performance, etc. These may not perform well enough to justify anyway. From what I can find the DC/DC convertors are pricey not to mention I have not found one that appears to be high amp or wattage.

 

[loquin]

I did a quick search also, and didn't see anything. I did run through TI's switching design software online and worked out an 18v to 12V switching regulator design, good for up to 21 amps... (which is the max rating of the output filter inductor)

I've attached the design, in case you're interested.

 

[Ypedal]

do you have a variable speed throttle for the motor ? or is it just an on/off switch ?

If there is NO controller, ie: if the battery goes direct to the motor, inline with a switch, more voltage will simply make the motor spin faster.

however, as said above, if there IS a controller involved ( black box that allows you to ajust the motor speed with a throttle ) then you need to investigate the controller's limits.

got pictures ? a model number ? etc.. ?

 

[bigriver]

MINN KOTA ENDURA 46 TRANSOM MOTOR 36" COMPOSITE

5 speed/off/ 3 reverse

I think the battery goes direct to the motor. The control wiring and main line voltage from battery all go down the shaft to the motor. Im thinking the controller does not carry any load because it is very light weight.

Thanks

 

[Ypedal]

http://www.minn-kota.com/Minn-Kota-faq/Minn_Kota_FAQ.htm#4

I would not use your dewalt batt for this application.

1 - the run time will be very short

2 - the multi speed switch / speed coil as they call it will not like the higher voltage.. ( it will likely work, but would more than likely die an early death.. compared to staying at 12v.. )

How big of a lead acid battery are you using now ?

ex: your 18v pack, if it had 2ah ( 2000 mah ) of capacity, contains 36wh if the motor draws 20 amps on high , it will only last ( 18v x 20 amps = 360w ) .. 360w / 36wh = 6 minutes.

And also.. 20 amps is too much draw for that battery... not good.

 

[bigriver]

75 AH OPTIMA 70 LBS "Run this one upstream until dead"

55 AH OPTIMA 40 LBS "Run this one downstream"