End of Successful Riding Season

[Tfisher309]

Having just pulled my battery for winter storage. It is a good time to share the experience I had with my electric motorcycle. First I would like to thank all the people who provide content on this forum. I could not have built the bike without your information.

The bike is a 1967 H-D Sprint with a qsmotor 138 70H V3, an EM-150 controller and a 74v 50ah battery. I built the bike last winter and road it about a thousand miles this summer. The bike is a joy to ride. Acceleration is strong up to 55 mph and it gets about 15 miles per kwh.

Something I wasn't ready for is the attention it gets. On the very first trip into town I came out of a grocery store and there was a small crowd around bike. This continued the rest of the summer.

To supplement the project and my electrical education, I constructed a home charging station. This solar cart provided 100% of the electricity the bike used this year. For the winter, the two batteries and inverter come inside and serve as emergency electrical backup for my house.

Thanks again. Tom

 

[99t4]

Great project on many levels. What's inside the gas tank? Those solar panel angle adjusting gears look seriously overkill. (not criticizing. Think I know where they came from.)

 

[SlowCo]

Very nice build and great way of charging it!
Doesn't the front mud guard (and tire) touch the battery pack when the front fork compresses by braking or even riding a seriously bumpy road?

 

[harrisonpatm]

To supplement the project and my electrical education, I constructed a home charging station. This solar cart provided 100% of the electricity the bike used this year. For the winter, the two batteries and inverter come inside and serve as emergency electrical backup for my house.

Consider this for next year:


Presumably you plug your 72V battery charger into the inverter? In that case, you have solar DC -> battery DC -> inverter AC -> motorcycle battery DC. Using a boost converter like the one linked above, you can go from 12v battery DC to 72v battery DC, skipping a DC-AC-DC conversion step and increasing efficiency. You can still use the inverter, you mentioned you bring it inside for backup power. But I'd bet you'd get 10% more out of your batteries by not using the inverter.

 

[Tfisher309]

Good comments, thank you.

The gears are the primary drive gears from the old Sprint motor.

From that angle it looks like the fender would hit the battery, but it doesn't, even at full compression. Since this picture was taken I did move the battery back closer to the motor.

The inverter is fairly efficient (about 90%), but the battery charger is a problem (about 65%). Even with these losses, on a typical day I can generate more electricity than I use.

The dc to dc charging idea is interesting, but to charge the lithium-ion battery on the bike properly the transfer would require some type of controller. If anyone could school me on how this could be done I would appreciate it.

 

[harrisonpatm]

The dc to dc charging idea is interesting, but to charge the lithium-ion battery on the bike properly the transfer would require some type of controller. If anyone could school me on how this could be done I would appreciate it.

The link in my post is one of several controllers you could use. The one I linked is specifically one that I have used for a year straight with no issue.

V-in is your 12v base battery. Connect with nice thick gauge wire, as thick as the input terminals will allow. This is also where you'll wire an on-off switch. V-out is where you'll connect the voltage output wire, for actually charging your bike battery. Use whatever connector that your battery accepts. Turning on the board's 12v input, use a multimeter to read the output voltage and use the trim pots on the board to adjust the output voltage to whatever you'd like your max battery voltage to be (with a safety margin). There, that's your charger.

The inverter is fairly efficient (about 90%), but the battery charger is a problem (about 65%). Even with these losses, on a typical day I can generate more electricity than I use.

If that's accurate, then that's not great. Say you want to charge your bike with 1000w. That means your inverter is putting out 1750w, your charger is putting out 1550w, and your bike battery is only seeing 1000w of that. Total efficiency of about 57%.

Whereas my boost converter setup takes my home's 48v battery boosted to my bike's 72v battery, and I've measured it at 85% efficiency, sometimes 90%

 

[Tfisher309]

I watched the video and can see the improved efficiency, but when charging my bike battery how would the boost converter know when to go into absorption and float stages? Would I rely on the bikes bms to shut things down?

 

[amberwolf]

when charging my bike battery how would the boost converter know when to go into absorption and float stages? Would I rely on the bikes bms to shut things down?

Are you using SLA? If not, those stages don't apply.

For a lithium pack of any chemistry I know of, you simply use a CC/CV charger or power supply (like an LED PSU, such as the Meanwell HLG series, HLG-600H-54A as an example I use myself). If the boost converter is a CC/CV output, then it does the same job.

If it's functioning correclty and wired properly, the BMS should disconnect the charge port when it reads any cell reaches full per whatever it's HVC is set to.

 

[harrisonpatm]

If the boost converter is a CC/CV output, then it does the same job.

It is.

Explained another way: say your top voltage is 80v. You set the boost converter to 80v output, then start charging. When your battery reaches 80v, then the boost converter has no voltage potential and current won't flow.

the BMS should disconnect the charge port when it reads any cell reaches full per whatever it's HVC is set to.

But you shoulnd't rely on this as your charging stop. If you set your voltages properly, the boost converter will just do its job until current stops flowing. BMS should be a safety HVC, not a regular-use HVC.

 

[Tfisher309]

The batteries on the cart are 12v 100ah lifepo4. The bike battery is 74v 50ah lithium ion.

I try to keep the bike battery between 72 and 82v. That gives me two days of riding (about 30 miles.) I rarely charge it all the way full. The bms shuts off at 83.6v.

 

[harrisonpatm]

The bms shuts off at 83.6v.

Sounds like you have 20s. 83.6v/20 = 4.18v per cell. Then if it were my project, what I would do is set the boost converter voltage output to 82.5-83v (and make sure my battery is top balanced). Then charging will slow and stop at 83v.

83/20 = 4.15v per cell, and you may already know that there's very little capacity gain between 4.15-4.18v anyway, so you're not actually losing any mileage. If something goes wrong, your BMS will be there to shutoff charging, but that shouldn't happen under normal use.

Keep in mind there's going to be an efficiency loss by going from something as low as 12v, all the way up to 83. The device I linked can do it, but with difficulty. You may want to consider wiring your two base batteries in series rather than parallel, the charge controller you're using can handle it. Though you may need a second panel in series to be able to get a high enough solar voltage to be able to charge 24v. And then you'd need a different inverter, if you'd still want to use the inverter, because you'd need one that can use 24v instead of 12v.... and I'll stop here, because this is how DIY projects expand beyond the original scope!

 

[Tfisher309]

Outstanding information. Thank you harrisonpatm. This certainly gives me something to think about as I consider scaling up my system to include an electric car.

I realize that when you transfer electricity there is a loss, but where is it going? My Kill-A-Watt meter says my 84v 8a charger is only 65% efficient, but when it is running, it and the connection points are barely warm.

 

[harrisonpatm]

I realize that when you transfer electricity there is a loss, but where is it going?

Still heat, even if you can't detect in with your hands. Just because the charger as a whole and the connections aren't warming up as far as you can tell, doesn't mean there isn't heat loss aggregating throughout the system. FETs, wires, resistors, ect, all losing a little bit here and there.

 

[Albie72]

Bike looks fantastic