Question -n Using ebike pack to top up 12V trolling battery (AGM) via MPPT solar charge controller.

I would like to use my big ebike packs to top up (in real time as I am trolling) an AGM gel cell 12v Battery...Can I just run the ebike pack through an MPPT charge controller directly to the AGM pack in parallel, along with my trolling motor from the AGM pack, as I am running the motor? Assuming the MPPT controller has adequate max voltage capability well beyond my lithium pack (say 100V MPPT vs 58.8 maxV lithium...that would give me a lot of extra trolling range...thanks

Sounds like a bad idea to me. First, isn't the 100V solar charge controller meant to charge a higher voltage bank of lead acid than a single 12V battery? Second, the voltage of the lithium pack doesn't seem like a good match. Third, what limits the current, since the ebike pack can deliver enough current to kill itself?

Instead of an expensive piece of electronics, a better option may be cheap DC/DC converters that convert the ebike pack voltage to 12V? Depending on the current draw of the trolling motor, you might even want several DC/DC converters in parallel.

An even better option would be a couple of Nissan Leaf modules in series as your battery. Then you get even more range without risk to your ebike pack, with no electronics to fail, a slightly higher working voltage for a bit better performance, and a simple cheap system with no electronics to fail out on the water...all in less size and weight than the AGM battery.

Thanks for your assistance...I failed my first attempt with a 48V to 12V DC DC convertor rated at 30 amps out, used to power golf carts. It ran for a while, but failed when my Minnekota was run at 100% for several minutes against a tidal current. I suppose if I hooked up two DCDCs of this size, it might be ok. Could I used two DCDCs with one ebike pack simultaneously?

An MPPT would be designed to put out around 14V, designed for lead acid, with a wide input range up to 100V. Not sure if it would limit the current of the pack though to some sensible amount say 10 amps.

I do have a bunch of old Headways that I could reconfigure for 12V pack as a winter project, but then I need a 12V BMS and a new charger, also a reasonable proposition. Or I could just buy a big lithium 12V LiFP04 (100amp hours) made for this purpose I suppose.

MPPT controllers actually already are very high efficiency DC DC converters, with broad input range, and low heat losses.

chvidgov.bc.ca said:

I do have a bunch of old Headways that I could reconfigure for 12V pack as a winter project, but then I need a 12V BMS and a new charger, also a reasonable proposition. Or I could just buy a big lithium 12V LiFP04 (100amp hours) made for this purpose I suppose.

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A 4s pack like that needs no BMS. You just act as the BMS. I only mentioned the Leaf modules, which are 2s and 60+ah, because they are the cheapest way to buy significant capacity. It sounds like a perfect use of your old headways though.