Is it normal for a CA to drain lots of power?

[benkels]

Hi just a quick question from a total noob. I was riding around on my bike when it hit the 60v minimum I'd set on my CA and so I wheeled it into my workshop and left it to sort out later. At the time it was reading around 62V. So I went out to the workshop to get something about an hour ago and noticed that I'd left the bike on and then noticed that the CA was showing something like 47v! So I've put them on to charge with my Icharger and it says that the lowest cell is 2.73V.

So I guess my questions are:
1. Have I just totally rodgered some of my pack?
2. Is it normal for a CA to drain that much when it's not doing anything or have I ballsed up the wiring?

My set up is an infineon 72v controller from ebikes.ca along with one of there cycle analysts and a HS3540 wired with halls from power in motion and 8 x 5s Turnigy lipos, 4s, 2p (74v, 10ah). When I wired it up the three motor wires were all back to front, yellow to green, blue to green, yellow to blue and the 5 hall wires all matched up colours wise. When I ran it with the wheel off the ground it drew less than 2 amps so I figured it was alright?

Any help much appreciated.

 

[dennyt]

The drain is probably from leaving your controller on, with the batteries at 3.0V / cell (you're running 20S, right?). They quickly dropped off the LiPo cliff with the minimal drain of the controller.

Set your controller cutoff to 3.5V/cell (70V) to be safe next time. You'll still have plenty of charge to play with (84V at 4.2v/cell).

Have you damaged your pack? Perhaps. Charge it up and find out!

 

[neptronix]

Yeah, 60V minimum is a terrible, terrible LVC for lipo.

60V / 20S = 3.0v/cell.

^-- standard discharge curve for all turnigy/zippy RC Lipo packs, this one in particular is a 20C 5AH pack.

You have about ~5% energy left after roughly 3.5v/cell. You have 0% energy left after 3.0v. Below 3.5v, your cell voltages will be all over the board as a 50mAh difference in the cells could mean a difference of up to 0.5v in a cell at that low of a voltage.

..and this is why it is important to know the basics about lipo before you start using it.
Charge your packs at a low 0.5A rate ASAP and see if you can recover the cells that went under 3.0v.

 

[benkels]

Thanks to both of you for your input. I guess I'll have to Change the LVC to 70v, which is a bit crap as I'd only managed about 10 miles range out of it when it was set to 60v.
I get what you mean about understanding the basics before using lipos but I just wanted to get on with the project and I sort of learn stuff by doing it, (by doing it, I mean screwing stuff up).

Thanks for the help.

 

[Ypedal]

a pack is only as good as it's single weakest cell...

In a perfect world, all cells would be matched 100% and remain in perfect ballance.. real life says this never happens.... unfortunately.

So, the pack voltage hit 60v, that one cell/group went quite far below 3.0v and bounced pack to 2.7, an hour on standby is no significant drain at all but when a cell is 100% discharged, it does not take much to take it from 3.0 to 0

 

[itchynackers]

Something isn't right if you are only getting 10miles out of 740wh. I couldn't use that much energy in 10 miles unless I was going uphill the whole way. What is your ride terrain like? What is your no-load current?

 

[benkels]

I'm in north devon, england and I guess it is pretty hilly. I actually just looked at the ebike.ca simulator and it gives a range of 9.7 miles WOT on the flat, so I guess thats about right. Although I have no idea what the internal resistance of my lipos is so just left it at .2 ohms, might be way out and I can't find any info on the HK website or on the rest of the net. Not sure where it states the LVC on the simulator either.

 

[amberwolf]

Regarding current used by the CA: I have the large-screen CA, and it uses about 7mA max. My 12FET Ecrazyman uses ~50-60mA idle when on. My inverter-booster + CFL taillight uses ~180-200mA.

So the CA itself is a minor source of drain, compared to everything else on the bike.


Regarding pack capacity, typically I would call a pack's usable Wh about 80% of what you get if you multiple the nominal voltage x the spec'd Ah. So in your case,
3.7V x 20s = 74V
2x 5Ah = 10Ah
74V x 10Ah = 740Wh
0.8 x 740Wh = 592Wh
So you'd have 592Wh usable (maybe more) to stay on the safe side of things. That means that at about 10 miles of range, you're using nearly 60Wh/mile, which is a LOT.

Regarding range, if you're really pulling 50-60Wh/mile, that's pretty hefty power usage. My 150lb CrazyBike2 plus my own 160lbs plus another 120lbs+ of dog food on a trailer is only 30Wh/mile, and that's with lots of complete stops and starts with cruising speeds of ~18MPH, average 12-14MPH over a 2.5-mile run.

26-30Wh/mile on just me and the bike for many complete stops and starts, 20MPH cruising and 14-16MPH average over a 20-mile run. Both of those with no pedalling. Even though it is mostly flat here, I still have a hard time imagining a regular-weight bike using double the Wh/mile of mine, even with lots of hills....

 

[Ypedal]

Clyte hs motor in fulll 26 size wheel and 72v .. full throttle all the way.. yeah it is possible but that motor must be hot when you get off.....

 

[neptronix]

At 3 volts per cell, even a tiny 1w draw would drain those cells rapidly on a 10AH pack. The cliff is real sharp once it hits on this chemistry.

10 miles on a 10AH 72V pack is about right for a Crystalyte HS / high speed type motor. The amp draw at those higher speeds is really high unless you're poking along at 20mph rather than about 40-50mph

[youtube]kBz53t6jdUg[/youtube]

^-- move over to about 2:00... good demonstration of the lipo cliff in action.

 

[Alan B]

Going fast consumes a lot of power, and so do hills. I'm running a just slightly smaller pack (18S 10AH to 9C 2810) on my 13 mile hilly commute and with a lot of vertical it still only consumes only 65% of the pack in the mostly uphill direction, and about 50% in the mostly downhill direction. That's at pretty much 20mph when under power and with some pedaling to help it out on the steeper parts.

 

[Ypedal]

I get get around 10wh/km on my 100v clyte 409 at 20 mph :wink:

My 100v X5 chopper however, going 40mph + blows thru power at 40 wh/km

convert that to miles and it's in the ballpark .

 

[dogman dan]

So true, all that above. You want to stop riding 20s closer to 72v, which could be about 70v under load.

And it's quite easy to use that much power, zooming around up hills. 50- 60 wh/m is not that extraordinary.

Fortunately you just barely stayed out of " ruined it" territory. You might be into, it will wear out a lot sooner territory though.

 

[SamTexas]

60wh/mi is really high. Are you riding on or off road?

I'm in north devon, england and I guess it is pretty hilly. I actually just looked at the ebike.ca simulator and itves a range of 9.7 miles WOT on the flat, so I guess thats about right.

What are the actual figures reported by your CA? Distance, top speed, average speed and wh/mi?

 

[neptronix]

Your mileage will vary dramatically according to your motor type, winding, wheel size, battery size, terrain, weight, pedal input, and speed.

Theoretically, I will see about 90wh/mi going up pike's peak, getting me a 25 mile range at an average of about 23mph up a constant average 7% grade. If i reconfigure the same battery pack to do 25mph on the flats on a different motor, i'll have about a 100 mile range at a nice even 25mph while pedaling.

The simulator on the ebikes.ca page is a great tool to understand all this.

http://ebikes.ca/simulator/

 

[dogman dan]

My personal best is actually about 55 wh/mi. Off road, trying to ride up 4x4 tracks too steep to walk up without falling on your ass. But the bike is only a 9c motor on 40 amps of 72v. On a typical dirt ride, 45 wh/mi is what I see.

Plenty of bikes built now using much bigger amps and higher voltage on bigger motors. Actually use 6kw and you won't be in 40 wh/mi territory anymore. In general, it's hard to use that much power on the street, unless you are really moving. But some do.

If your bike does 40 mph, and you are cruising on the street, you can pretty easily drain 72v 10 ah in 10-15 miles.

 

[hjns]

My bike does 36mph on the flat at 84V HOC (hot of charger) with a 20S3P 13.5Ah Lipo pack.

When commuting, I spend 666Wh/33km (multiple commutes on one charge) = around 20Wh/km = around 33Wh/mile. And this is with a rear Clyte HT3525 hubmotor, in town, with accelerating to WOT and decelerating to stop for traffic lights, and only 1 short hill of 20%.

With more hillies, or pulling a trailer, it easily doubles.

 

[dogman dan]

Just put up a new vid in the pics section, of a gnarly hill climb. 105 wh/mi on just the climb. I suppose about 60wh/mi of that was simply making heat. The last 100 ft of the climb is stall city.