RC Lipo's

[deanoseadog]

Is anyone using the soft Lipo cells, like in RC planes etc. I have some in my RC car and plane and there performance is Soooo much better than the NiMH I had before. When I built my first eScooter I was interested in making a Lipo pack for it but the cost was still really high (3 -4 years ago).
But, I just had a look on ebay and found a place in HK selling RC packs with 4000maH cells that were rated at 15C burst, 10C continuous (i think RC idea of continuous is about 8mins), working out to about AUD$4.20 each cell and even with shipping to Aus, 48V 20Ah's worth of cells was only going to cost around AUD$550. Now I know that the equivalent ping battery is only US$770 and that includes a charger and BMS, but it seems that the BMS is the bottleneck for the current. So what if I bought HEAPS of these "cheap" lipo's, and a couple of balancing chargers could I really get a 48V 20Ah pack that can can supply 300A peak? I realise that without a BMS I run the risk of ruining a cell on discharge etc.etc. But at these prices I could get an extra 10A of battery and just leave a bigger safety margin with my "seat of pants" LV cut-off.

So basically what I'm wondering.....has anyone tried it? Willing to try it with their own money first?
C'mon I know you want to see my chopper go with 96V worth of Lipo's on board @ 12kg rather than 48V of Pb @ 30kg!

Ok just saw Ping packs for US$598. Better, but stil only 60A peak current.

 

[deanoseadog]

OK, used search function, found a little info.

 

[tostino]

Keep in mind those lipos will only last 200-500 cycles before you need to replace them.

A ping pack will last over 1000, and it claims 2000 but hasn't been tested yet.

If you need the speed, go for the lipos, otherwise stick with ping.

 

[deanoseadog]

Yeah, If I was building an ebike I would probably just buy the ping pack. The problem is I need 100A continuous and 200A peak (preferably 300A peak). Range is not so much of an issue though, so ideally a 20-30Ah pack with 10-15C burst, 5-6C continuous. It seems the individual cells could do it (the better ones anyway) but the BMS seems to let them down.

 

[tostino]

Yeah, If I was building an ebike I would probably just buy the ping pack. The problem is I need 100A continuous and 200A peak (preferably 300A peak). Range is not so much of an issue though, so ideally a 20-30Ah pack with 10-15C burst, 5-6C continuous. It seems the individual cells could do it (the better ones anyway) but the BMS seems to let them down.

Hrmm, you may be able to add solder to the BMS shunt to raise the current limit, as well as possibly being able to get a larger amp hour pack which would help keep the C rates down.

Talk to Ping and see what you could do. I don't think you can get 200 peak, but 100 continuous should be attainable.

You could also possibly either try and get 2x 48v 16ah, or 20ah and parallel them together for a higher possible amp draw, and drastically increased range over the Lipo pack, if it is financially feasible.

What are you using that could draw 300 peak amps at the battery? Even Kelly controllers most likely won't draw 300 amps at the battery peak.

 

[deanoseadog]

The motor is an Advanced DC K91, and controller is an Alltrax 4834. Controller is rated at 300 A peak for 2 mins, but my Pb batteries don't get to that anyway. So 200 would probably do, though the motor seems capable of pulling 400-450A. It's a bit big for my mini chopper, but it was cheap. I have been eyeing off the 96V kelly and trying to gather info on batteries for the inevitable choppa mk2. So if I could get a 48V 30-40Ah pack now (or parallel 2x20AH) and then add another 48v pack when I get the bigger controller. That would be great. Oh and I think the Kelly is rated at 400A peak for 1 min, but realisticaly I don't want the motor to run at more than 70-100A cont. and prob 200A peak would do. I would rather have a higher voltage and lower current.
So does Ping do custom BMS's and battery packs?

I looked at paralleling packs a little while ago, but from what I have read (a while ago) most of the BMS's don't like it. Couldn't find much info on what actually happens, but heaps of negative speculation. Has anyone tried it recently with these new and improved cheapo li batts?

 

[tostino]

I honestly have no first hand experience with Ping packs, so please don't take what i'm saying as fact. I just read these forums a lot, and have read about other people's experience with them.

The last news I heard was that the new BMS could cope with paralleling packs, however, I don't know if that is true or not. Correct me if I am wrong, but as far as I know the way to get around this, is to just use a diode on the wires coming out from each pack. That should protect the BMS.

It looks like with a motor that big, pulling that much current, the large pack size is not a negative factor at all. It seems like your range would be so heavily restricted with anything less than 60ah. With a 60ah pack, you should be able to pull 120a continuous, and 180a peak without modifying the BMS at all, and keeping the warranty intact. I'd love to have almost 3,000 watt hours at my disposal!

I have heard that Ping will work with people on custom sized packs, so shooting him an email probably is a good next step.

 

[mingonn]

Hi deanoseadog;

Go lipo mate, I run a 44.4v (3x14.8v) 3800mah packs. Bought the cheapest I could find on ebay and they have done 1100 km already no problems, I haven't even had to balance charge yet as the cells have stayed within .01 of a volt.

If you use deans plugs you can easily make a parallel charging /series discharging harness, I have been charging all 3 packs in parallel at 4 amps (which works out at 1.3 amps per pack).

That said, I limit my maximum current to around 6 amps not 60 peak/ 40 continous and don't believe the ratings on the cheepo lipos either, they are over stated.

Just treat em well, regularly check individual cell voltages, watch you don't over discharge and where you charge or with that much lipo it could get ugly.

Derek

 

[tostino]

I found some RC lipos like the poster above was talking about. That doesn't seem like it's all that bad of a route to go, however, you won't get ANY lifespan out of them if you run these cheepies at 5-10c.

The ones I am talking about can be found here.

To make a 44.4v 24ah pack, you would need 18 batteries (9 orders of the link I posted). You would hook them up 3s6p to make your pack. Including shipping you are looking at spending $432.00 on the pack alone, which honestly isn't that bad. You will also need chargers though, and a few of them to be able to charge your pack in a reasonable amount of time.

This smaller pack should be able to pump out the amps you need for your motor with the smaller ah size than a ping solution would, at the sacrifice of range and lifespan of the pack.

If it were my project, I would want to be able to go on a long ride if I chose to, and not have to replace my pack after only a few hundred cycles.

 

[deanoseadog]

Yes, those were the lipo's I was looking at. At the moment I have 26Ah AGM's in the chopper and the range is OK. The actual Ah is really like 16Ah thanks to puekert. I get about 15Km out of them. So I figured 20Ah of lipo's would probably give me close to 20Km range since they don't seem to suffer from puekerts effect so bad.If I could aford it I would love 40Ah, and I see some of the packs are getting up to that sort of size now but the current rating still seems to be the same as the 20 Ah packs so I would rather parallel two of those.

I already have a lipo charger that can charge up to 5S at 5A so the parallel charge/series discharge harness would be the go.
Thanks for all the replies. I might shoot an email to ping and see what he can do.

 

[stew007]

Wow, that is an amazing price for Lipos. You should get 500+ cycles no problem with lipos if you keep well within there rated specs, never discharge below 3.3v per cell and if they are 15c rated then try to run continuously below 7c and if you have to store them for longer than a couple of weeks, you have to leave them between 50-60% state of charge and this gives them a much longer life span.

You can balance charge these packs in parallel by making a parallel lead for both the balancing taps and the main -+ terminals, but you must! connects the balancing taps in parallel too, then it's just a case of finding a nice charger, like http://www.allerc.com/product_info.php?cPath=9&products_id=3366 with one of these to power it http://cgi.ebay.com/400W-24V-16-7A-Switching-Power-Supply_W0QQitemZ190277223440QQcmdZViewItemQQptZLH_DefaultDomain_15?_trksid=p3286.m20.l1116

I use the esc from ebikes.ca they can plug into a cycle analyst which can be programmed to limit the current to your desired wattage, and also be programmed for your desired low voltage cut off, so that combination is perfect for LiPo batteries!

 

[tostino]

Nice charger: http://www.rclovers.com/

Edit: And power supply to go with it: http://cgi.ebay.com/400W-13-8V-29A-Switching-Power-Supply-RADIO_W0QQitemZ360120494459QQihZ023QQcategoryZ20589QQcmdZViewItemQQ_trksidZp1742.m153.l1262