Upgrading toy hauler solar and battery to charge eletric toys

[brianjonesphoto]

Hello all
I'm investigating the best way to charge our eletric motorcycles while camping without a generator. We have 4 bikes with a total of just under 7k WH of capacity. I'm looking to build a system that has enough capacity to recharge all 4 bikes from dead overnight. Realistically it's highly unlikely that all the bikes will be completely dead at the end of the day.

Currently we have 200 watts of solar and a 150ah 12v LFP battery managed with an Electrodacus bms and controller, and it more than meets our eletricl needs for the trailer.

What I'm considering is building a 24v 7200WH system (8x304AH cells) and adding 4, 300+ watt 60 or 120 cell panels. In theory this should give me enough solar capacity to recharge whatever is used overnight to charge the bikes with bit of a cushion.

I've done some measuring and the chargers for the bikes are only about 85% efficient from 120v AC source. I'm loosing roughly 60-100watts from each charger. That added to inverter losses is a significant amount of wasted capacity. I'm thinking about using cc/cv boost converters for a dc>dc charger to step up the 24v to the 54.6v and 58.8v the bikes need. This "should" get me at least 90% hopefully closer to 95% efficiency. With all 4 chargers running it would be appox 120amps draw from the battery.

I'm looking for some feed on this concept. Is there anything major that I am missing?

Thanks.

 

[rmaddy]

Definitely avoid using an inverter. No sense going from DC to AC and back to DC. Why not build a 48V battery? Use 16 140Ah cells. You still get about 7200Wh and your voltage will be more like 52-54V which will be a lot easier to use with the bikes. Charge the bikes directly from the 7200Wh battery.

Recharge your 7200Wh battery during the day with the solar while you are out riding the bikes. Then hookup the bikes to the fully charged battery overnight to recharge the bikes. Repeat again the next day.

 

[brianjonesphoto]

Definitely avoid using an inverter. No sense going from DC to AC and back to DC. Why not build a 48V battery? Use 16 140Ah cells. You still get about 7200Wh and your voltage will be more like 52-54V which will be a lot easier to use with the bikes. Charge the bikes directly from the 7200Wh battery.

Recharge your 7200Wh battery during the day with the solar while you are out riding the bikes. Then hookup the bikes to the fully charged battery overnight to recharge the bikes. Repeat again the next day.

I've toyed with that idea too. The down side is mainly cost and complexity. I really like the simplicity of the Eletrodacus system and it only supports 8s systems.

 

[rmaddy]

I thought you were talking about making a standalone system just to recharge the bikes. Are you talking about replacing the existing 12V solar system in your trailer with this new 24V system? You'll need a converter go to down to 12V for the trailer stuff and you'll need a converter to go up to 48V for the bikes.

 

[brianjonesphoto]

I thought you were talking about making a standalone system just to recharge the bikes. Are you talking about replacing the existing 12V solar system in your trailer with this new 24V system? You'll need a converter go to down to 12V for the trailer stuff and you'll need a converter to go up to 48V for the bikes.

Well you bring up a good question, I had imagined it being a replacement. Yes I know I would need at converter for the existing system. Each bike will need it's own converter/charge controller regardless of the battery voltage.

 

[time2roll]

I would be inclined to build the system a bit larger and accept the inverter losses. This keeps it user friendly for all to use the charging at will. No modification of the toys and controlled charging as determined by the manufacturer. If the 8 cells is not enough I would save space to add a second battery.