18650 cell battery in series with Hobby King lipos.

[mistercrash]

I was sure there was a thread about that but I couldn't find it.

I have a 16S20P battery made from Makita 18650 cells. I charge it to 64V and don't let the voltage drop below 56V. I tested that this gives me 23Ah to work with. I have two speeds on my controller, low and high. I always use the low speed because the high one is too fast and I don't want to burn up the motor. I run a heavy scooter and I'm a heavy guy. On 16S the low speed is barely 30 km/h. I'm wanting closer to 35 km/h.

Go see this please: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16226

Can I get three of these in parallel and connect them to my 18650 battery in series to get 20S? I would charge to 80V and not discharge below 70V.
Will these HK lipos help with voltage sag a bit?
Is this a good idea?

Thanks
Ray

 

[imorton]

What about just using your "high speed" portion of your controller, and just reduce your throttle usage to maintain 35kph…?

IAN…

 

[dogman dan]

Well, then you'd be too fast again at 20s.

I'd say fix sag by paralleling in more of the same voltage.

 

[imorton]

Can you not just use a CA and limit the speed…?

IAN…

 

[dnmun]

do you use a BMS now to protect the little 18650's?

i second the dogman and you should use 16S of the lipo in parallel and use the same 16S BMS but charge to full charge at 67.2V because you are leaving 10% capacity unused now on top and about 3% on bottom if the pack is balanced by the BMS. that is worth a few mph easily.

 

[mistercrash]

I like switching to the low speed for long distance rides, it keeps my hand from cramping up, the speed is governed so my hand just sits on the twist grip, instead of holding it in a certain position to hold a certain speed. I went back to the original controller that has no plug in for a CA, I would have to buy the parts needed to install it the other way. The CA I have is defective, the right button stopped working again so I would have to buy another CA while I'm at it.

30 km/h on low speed is too slow, I want more like 35 km/h. I was under the impression that to have more speed, you need more voltage, not more amps. I agree more amps would help with voltage sag but I'm confused on how it would give me more speed, especially since the controller is not programmable, or maybe it is but I don't know how, it's just some common Chinese controller in which I built up the traces and did a slight shunt mod. I was simply going with personal experience, I was running on 20S before and the low speed was satisfactory at that time. I went back down to 16S to use the original controller which had 63V caps. I changed the caps to 100V ones so I thought of going back to 20S to raise the speed a bit but use high C rated lipos instead of adding more 18650 cells. I thought maybe the high C rated lipos would absorb some of the sag of the 18650 cells under acceleration.

No I don't have a BMS to protect the little cells. Since I started using them two+ years ago, I found that they are much better at holding a good balance, a monitored balance charge (with a BC168)once a week gives me a good idea if there is problems arising with one of the cells. I read in here about the LiFePO cells often seem to be unbalanced and absolutely need to have a BMS, I saw for more than two years using the Makita cells that they keep a better balance, and if a battery is left to rest for a couple weeks, the cells actually become close to perfectly balanced by themselves.

 

[dnmun]

when you raise the voltage on the controller you also have to raise the input power resistor values to keep the voltage that the regulator sees on it's input to something less than about 50V. so then you could use the controller on 20S, or 84V.

if you use the lipo in series with the konions then there is a difference in resistance seen by the lipo during charging so it should be hard to get the pack to balance.

if you keep the 20S of konions and add 20S of lipo in parallel then each channel should have equivalent resistance and it should be easy enuff to balance. but that is an assumption. i would recommend a BMS to protect it from allowing the lipo to climb out of the charging limits above about 4.28V. maybe the konions can do it, maybe not.

 

[mistercrash]

Yes you make me realize something. The konions can take quite a lot of abuse, but not HK lipos.