Are Lead Acid Good Enough?

[Lollandster]

Hi, I have just ordered the SmartPie DIY kit without the battery. My initial though is to buy some cheap sealed lead acid batteries and use those until I feel comfortable spending ~$400(incl shipping) on a lifepo batterypack. In the spirit of keeping the cost down on the lead acid, as it is only temporary, what is the smallest battery size I can use and still get enough current out of it? I was hoping I can use 4.5Ah batteries as I think that would be enough for now (I don't intend on traveling more than a couple of km daily). If I have to go up to 7.2Ah it is also ok, but if I need more than that I will have to consider buying lithium.
Thanks.

[truly_bent]

What type of bike is this going onto?

- How big (what diameter) is the wheel?
- How fast do you want to go? (Voltage)
- How far do you want to go? (Amp Hours)... Okay you've already said two km, but that seems very low.

Example: If you have a 26" wheel and want to travel at 45kph, you'll have to run at 48V. I can tell you that, given that configuration, 4.5AH will get you close to 20km, no pedaling... using LiFeP04. Not quite sure how that equates to lead acid, but I would hazard to say they're not far off. Lead acid won't survive deep discharges as well.

Anyway, you'd have to stack 4 said batteries in series to get your 48V. Can you carry 4 of those?

Jeff

[Lollandster]

My bike is 26inch and and I was gonna go for a 36V setup using three 12v lead acid batteries or two 5s LiFePo4. My question is about the amount of power these lead acids can deliver. From what I understand the smartPie is about 10A continuous so for the 4.5AH lead acids to work they'll have to be able to deliver 2.3C continuously and probably a lot more at peaks. But I don't know anything about closed lead acids. As I said this is only a temporary setup I'll upgrade in a month or so. I just want to get a feel of my power needs. ~24V (250w) would be the maximum legal setup, but I'm willing to stretch the law a little if I need all of the 400w to be pleased. Testing with 36V seams like a good idea to me.

[truly_bent]

Looking at the stats of the SmartPie http://goldenmotor.com/SMF/index.php?topic=4282.0#lastPost, one finds that the little beast will require more amps than you might think.

At 70% max rpm (an unofficial "loaded speed" marker), you'll be drawing 500W (at 36V), requiring about 13.9A. That's a full 3C. I don't have sealed lead acid stats in front of me, so I can't advise you as to how long the batteries will survive that.

Jeff

[Lollandster]

Looking at the stats of the SmartPie http://goldenmotor.com/SMF/index.php?topic=4282.0#lastPost, one finds that the little beast will require more amps than you might think.

At 70% max rpm (an unofficial "loaded speed" marker), you'll be drawing 500W (at 36V), requiring about 13.9A. That's a full 3C. I don't have sealed lead acid stats in front of me, so I can't advise you as to how long the batteries will survive that.

Jeff

Thats interesting. Why would they say 400w at 48V if it really can do close to 700w? I thought most companies lied the other way, stating more power than they can deliver. I did order the programming cable too so I may limit it somewhat to keep it legal.

I am about to give up on this and just order a normal battery. Does 36V vs 48V do much difference in hill climbing or is it just top speed that is effected?

[truly_bent]

At 48V the Smart Pie runs about 700W. That's 14.6A - up from 13.9A at 36V. That's not much of a torque increase, but your speed will go up by about 25%.

As to why rate them at 200/400W, you'd have to ask GM how they derive their ratings. Personally, I think it's market driven. Europe and Australia have much stricter limits on wattage than we do. 200/400W systems are about as good as it legally gets in many places. Nice to have a little more under the hood than is on the nameplate.

Might be why GM prints their motor stats in Chinese.

Jeff

P.S. They shoulda called it The Sleeper

[Morgen 3Eman]

Hi Jeff,

So are you telling me that my Lyen-ized 1KW MP3 drawing 45 Amps from a "48 Volt" battery that puts out 58 Volts is producing more than the legal 1KW?  I'm shocked!!!  Just shocked! 

(But it is a bit of fun)

TTFN,
Dennis

[Bikemad]

So are you telling me that my Lyen-ized 1KW MP III drawing 45 Amps from a "48 Volt" battery that puts out 58 Volts is producing more than the legal 1KW?

Dennis, there's no need to worry, you simply need to explain the facts to the nice policeman:

"I'm sorry officer, but I'm sure you'll find that power output of this very inefficient induction motor is well below the 1kW maximum legal limit, let me explain in more detail:

Firstly, Power In = Volts x Amps = 58 x 45 = 2,610 watts.

You now need to understand that the Actual Power Output = Power In x motor efficiency = 2,610 x 0.35 (35%) = 913.5 watts.

So, you can clearly see that the power output is considerably less than the legal limit, therefore I am not breaking any law."

That's basically all there is to it

Alan
 

[Lollandster]

I am considering buying a 36v10Ah LifePo4 battery  with the folowing stats
Maximal Continuous Discharge Current: 15Amps.
Maximal Discharge Current: 30Amps.
Will this be good enough for me?

EDIT:
Never mind, I just ordered that battery. I just hope it doesn't take too long for it to arrive. It's about a week since I ordered the smartPie so I'm expecting that to arrive long before the battery. It's going to be frustrating to own a smartPie and not being able to test it...

[truly_bent]

Love the justification Alan. Just enough truth to confound.

lollanster;
That battery looks like a good fit. You may even find the range exceeds your expectations.

You would be well advised to look into getting a Cycle Analyst (http://www.ebikes.ca/drainbrain.shtml). Takes the guesswork out of running one of these rigs.

Jeff

[Lollandster]

Love the justification Alan. Just enough truth to confound.

lollanster;
That battery looks like a good fit. You may even find the range exceeds your expectations.

You would be well advised to look into getting a Cycle Analyst (http://www.ebikes.ca/drainbrain.shtml). Takes the guesswork out of running one of these rigs.

Jeff

Thank you, I was wondering where I could get one of those. For now though, I have used much more money on this project than I was planning so the cycle analyst will have to wait. My original plan when I stated looking at ordering an ebike kit a week ago was to buy the cheap kit on ebay for $220 incl shipping combined with lead acids. I'm currently down $864 incl shipping for the smartkit and battery and I'm expecting import tax/vat to come too.

[truly_bent]

That's a big enough bite.
Hope you enjoy the result.
J

[Sangesf]

What batt did you ultimately go with?

[Lollandster]

What batt did you ultimately go with?

I went with a battery from bmsbattery com. I believe the limit of 15amps is because of the BMS.

[skylinenitro]

One thing I do like about lead acid is that it starts to slow down when it drains low, with Lipo or equivalent, you run strong until it just quits.  But then I don't have a BMS or even a 48v throttle.  I run 48v Lead with a 36v throttle (so it always says I have a charge until I'm too late)

I also like baing able to use any dumb charger to charge my batts, don't have to worrie about over voltage or special chargers.  But that said, I am working on a Lipo pack because of the weight savings...