Using Trolling Motor with SLA and 48V/12V DC DC together...

[chvidgov.bc.ca]

I recently aquired a 48 to 12V DC DC converter (putting out 30 amps max), with the intention of running my trolling motor on my 48V ebike battery. I gather the converter puts out a square wave "dirty" 12V power signal that could damage my Minnekota DC brushed motor. Is that true?

If it is a problem, could I use a deep cycle SLA connected to the motor, with the 48V/12 converter hooked up in parallel to that SLA battery, so that the load is shared between the SLA, and the converter (powered by my ebike battery)? Would this "condition" the power of the converter, as well as provide more than enough amps for the trolling motor? The motor can spike to around 40 amps on the top setting (it is the Maximizer PWM type of Minnekota).

Otherwise, could I charge my SLA with the 48/12 converter (12 to 12)? Or with the 48V DC directly connected to the AC of a normal 12V charger?

I'd love to triple my range with a big LiFPO4 in the mix, through the 48/12 converter...

Thanks,
Chris

 

[major]

Does the Minn Kota trolling motor have a speed control? If so, that might not tolerate a converter in front of it. But I suspect the DC motor itself would run fine off of a converter. Afterall, that is what a DC motor speed controller is; a converter. Your problem may be in the starting of the motor without a current limiter, which DC motor speed controllers usually include. So connecting the 48/12V converter to the motor will draw an inrush exceeding the 30A limit and may fault your converter.

 

[chvidgov.bc.ca]

It has a continuous throttle from low to high speed, not the 5 speed non-maximizer. Just like an ebike throttle. The "inrush" you mentioned - wouldn't that happen with just a regular deep cycle SLA as well? Which can put out well over 40 amps on a spike. By "converter" I mean the 48 to 12V step down "buck converter", not the controller in the motor itself that it comes with.

 

[major]

Yes, I assume what you call a 48V/12V DC DC is a converter of some type, PWM, either a buck converter (which would be non-isolated) or a forward converter which is isolated. Since your trolling motor has a speed controller on it, good chance it is also PWM and a buck converter. So, running 2 converters in series is problematic.

The motor speed controller likely has a current limiter. Trolling motors won't have a large inertia to accelerate but will still draw an inrush of high current which I suspect is well over 100A unless there is a current limit.

I guess you could run the 48/12V converter into a 12V battery and then the motor with its speed controller after the 12V battery. But you will have no charge control for the 48 into the 12V. But WTF? Give it a try. I'd use fuses in case something fails full on.

 

[chvidgov.bc.ca]

Thanks...I'm not sure I know enough yet to try this. Don't want to damage the new motor.

 

[dogman dan]

Just smooth out the 12v DC by running it into a lead battery on the way to the motor. Doesn't have to be huge, 12v 20 ah plenty.

But of course, don't hook your 48v to 12v converter to a completely dead battery, or it might try to charge the battery so fast it would blow. Hook it to a fully charged battery, and just run on the battery, which will be getting recharged as it goes.

 

[chvidgov.bc.ca]

Thanks a lot Dan..that's what I was hoping to hear might be possible.

 

[chvidgov.bc.ca]

Hi Dan...I have another question related to the trolling motor question...my DC DC puts out 12.62 Volts on the voltmeter, after stepdown from 48 on my LiFP04. I checked the end/charged voltage of a couple of fully charged lead acid batteries and they ran around 12.77 approximately. Is it ok to hook up the converter to the battery before the battery is allowed to drop a bit so that it is equal to or less than the 12.62 of the convertor? Or will this create a problem pushing energy backwards into the converter? Would it also try to charge the 48V lithium a bit or just blow the converter? I just read that 12.62 is the approximate voltage of a lead acid battery at 90% SOC. Perhaps I need a diode to prevent backflow to the converter?

Thanks.

 

[dogman dan]

Diode would work for sure, to make that flow one way. I'd just undercharge the lead to 12.5 or so, and then hook up. But try not to hook up with the lead a lot lower. A cheapo voltmeter after the lead would tell you when to hook up. Likely 10ft from the dock if it's a small lead battery.

Back to the first post, I'm assuming your converter can run fast enough to supply the cruising amps draw of your trolling motor.

 

[major]

A diode at 30A will be about 20 Watts and need a heat sink or at least air-over. You should not need one. Buck converters will not backfeed. I'm 99% sure your DC/DC will be o.k. with a bit higher voltage on the output. It will just not start to function until it senses a voltage on the output lower than its set point. If you're concerned, do as dan suggests and connect after the 12V has dropped below your set point. And step down converters cannot feed back to the source. No way could the 12V battery charge your 48V. They do make bidirectional converters, but little to no chance that is what you have.

 

[chvidgov.bc.ca]

ok...thanks guys...I'll give it a shot, once the marine forecast improves! I'll let you know how it goes.

 

[chvidgov.bc.ca]

It works ok! Apparently. I took a gulp and hooked up my small 48V Headway pack via the DC DC directly to the trolling motor, without the intervening AGM battery in parallel - it worked fine that way; The wattmetre on the ebike battery output indicated an amp draw of 6amps at 53 volts when the Minnekota Maximizer Endura 40 throttle is at 100% - 318 watts, through to the DC DC converter. Which unit is supposedly is rated at 30 amps output - it has that on the case - that makes sense, as the Minnekota at that moment was happily churning out a massive water wake in the garbage can water on the 100% throttle setting. It sounded totally normal, and seemed "hotter" (powerwise) subjectively than the AGM (Trojan 80Ahr deep cyle) source or at least as hot (less voltage dip with the DCDC). The DC DC didn't appear to overheat or "blow". My 20 amp blade fuse on the DC DC output line to the motor was not blown, something else I noticed. I should have had a 40 amp blade fuse in there. Can I assume that it is safe to run it this way as the test was so successful? It seems to run identically to "just the AGM", but using my lovely ebke battery. I was also pretty pleased with the motor efficiency. The end voltage after 5 hours on the ocean on the AGM seemed decent, at 12.28 on the AGM. With maybe 5% of runtime on the 75-100% throttle range. I did have my ebike battery/converter connected to the AGM the whole day, but I couldn't prove that much current had flowed from the ebike side. If the DC DC were 100% efficient, it could put out 25.44 amps (at 12.5 volts) - which might hold on the 20amp blade fuse. Evidence indicates .4 horsepower from ebike battery with no issues apparent so far. Pretty pleased. And we caught dinner - a nice 10 lb. cabezon off Victoria waterfront today. Life is harsh in beautiful B.C. I should be able to hold the fishing canoe at 100% throttle for many hours if I had to now.