Your opinion matters

[Jay-Fayzed]

So to make this post quick and dirty..... I built two bikes for my kids to keep up on some trails( I'm riding a NON assisted bike) I used a cheap Chinese kit and so far am very impressed with it. The question is my battery chemistry I choose. I constructed two battery packs 10s 3p 5amh using LiPO. Crazy right? What kind of guy straps this between his kids legs and sleeps well at night? Well that's why I'm asking your opinion perferably and educated one. In two years Ive been using LiPO in various RC and electric ride on toys ,I've never had a fire or any noteworthy I'll effects. My thought process was that the battery is rated at 25c, or 125 amps! My controller is rated at 14amps, on the LCD display I can see motor watts instantaneously and the highest has been 625 watts pulling me so that should be almost 15 amps, or 3C's. Which I should also state none of my LiPOs ever get charged more than 4.12 per cell. Moving along , the LCD display/ controller has a LVC @30 V. Which technically is 3v per cell which is a no no. So to counter this , my kids know when the battery gauge is on its last bar to check the pack voltage on the display . They know when it reads 33v it's time to bring it in or shut the power off. Last note is that they only ride the bikes with me present and I'm never more than 20 meters from them. Those little bikes can scoot uphill better than I can. So should I source safer battery chemistry or does these practices negate most of the failures associated with LiPO?

 

[emmetbrown]

As long as you take care of charging the packs in a safe place and are near when the bikes are ridden where's the problem?
In a proper charge-setup differences between cells will be eliminated, so even with manual LVC you should be fine.

 

[Jay-Fayzed]

Thanks. I felt the same way but there are some people who feel strongly that LiPO is still a bit too unstable for children to use them. And in to a point that's true , like you stated, I handle the charging of the packs And if they sit for a few days I go ahead and discharge them to the store mode capacity. I just have a few RC buddies who loved the kids bikes but showed a bit of concern about using LiPO. To be fair though one of my friends has had a fire, but it was his own fault.

 

[Ykick]

Sounds like a great opportunity to teach respect for powerful batteries. Fully supervised I have no problem with your plan.

 

[wb9k]

It's all about having diligent processes and adequate hardware . Most cells can be made reasonably safe, even for use by kids. You seem to be doing a good job with charge management and pack sizing. You don't mention how the cells are contained on the bikes. I would want to see them contained in a metal box to protect them from impact and to contain any thermal events that might happen while being ridden long enough for the rider to get off the bike without getting badly burned. Only you know how well your kids do or don't listen. Sounds like you're doing fine overall...just stay vigilant....always.

 

[Hillhater]

No, our opinion is not the one that matters.
Its yours that counts.
If you rest easy safe in the knowledge that the risks are under control,..then fine.
BUT,.. If you have uneasy nights thinking of the possible risk, despite all your good battery management, then you know its time for a chemistry change. ! And since you took the time to come here to ask, i suspect you are not 100% comfortable with the current set up.
Could be a good educational exercise too , to work with the kids and build a nice compact, lightweight, 18650 pack of the same capacity, to show them the options..
...and let you rest easy at night.

 

[Jay-Fayzed]

The frame bags are fabric , but the batteries are hard cased. I'm actually working on building a frame out of 6160 aluminum. When I get more progress I'll post up that build. But for now think of a mini stealth bike. Issues are no one really makes a good fork for 20in bikes or 24in bikes. But on topic I too rather a safer battery compartment. My kids do know to stop a fast as possible and ditch the bike if for any reason they think something is getting hot.

 

[Jay-Fayzed]

@hillhater: I'm actually considering biting the bullet and paying the bigger bucks for a proper 18650 setup, but for the new frame I'm going to build. I want a simpler charging setup for the future. But I'm never 100% confident in my own work! im like 98%! Beyond good practices I figured putting a 30amp inline fuse on the positive lead would ensure I never come close to discharging to quickly, and I wired in a simple off on switch on the negative lead so I have a master OFF switch. It's not much but I figured it's something. Do you know where most people buy good 18650 cells from ( keep in mind I'm in the U.S. ) thanks.

 

[Hillhater]

There are several good threads on this forum about 18650 buying and pack building, have a read through a few for trusted sources.
this is one of them.. http://endless-sphere.com/forums/viewtopic.php?f=14&t=57291
Also be aware that in line fuses may save an overloaded pack, but it wont help with an internal pack short or thermal event caused by a bad cell etc. ! :wink: