Motor AMP draw

[cgbjake]

So I'm getting ready to pull the trigger on getting a battery pack to replace my NiCD pack that is dead. But I'm concerned about how many AMPS I'm drawing through my motor and can't get a reading on it. My pack is pretty well dead, not a lot of life left so I am concerned that I won't get max AMPS when I put my watt meter on it. (have not put a meter on it yet, not motivated to because of above but will if others recommend it) Can anyone tell me how many AMPS my Great White scooter 800W motor is using, 36V through a Curtis Controller rated @250 AMPs will draw? How do I figure this one out? I'd like to get a 36V 15AH Ping

http://www.pingbattery.com/servlet/the-9/36V-15AH-V2.5-LiFePO4/Detail

It's labeled as using only 600 watts max, but I hear from Headway Headquarters recommends a 16 AH use 550-850 watt motors. Obviously my controller can handle a lot more AMPS than the batter/motor so I'm curious what I need to do. Do I need to upgrade to the 20AH pack where I can get a stronger BMS or can I get by with the 15AH from Ping (don't offer an upgrade in BMS at this AH)? I am running a pedal assist bike with a SRAM Dual drive on the back so I have 3 gears to choose from. I pedal a little, but use the motor a lot of the time. I'm pretty easy on my stuff but would like to be able to accelerate heavy when I need it.

Any help that you guys with smarts can offer would really help. Thanks guys/gals!

 

[skeetab5780]

well this probably wont answer your questions but you do realize that a 36v 15ah ping is rated at 30amp max discharge? and really only 15a constant. your 800w scooter motor is rated at a continuous 22.2amps at 36v. so it seems you chose a good battery for your motor, but that controller may damage both your battery or your motor if it is not properly current limited. if you insist on using that large of a controller to get you up large hills with ease, you may need to look at batteries with higher C ratings.. Eg: custom built a123 pack from cellman or maybee you can go with LIPO RC packs and then you will have no problem burning up that motor.

 

[jimw1960]

well this probably wont answer your questions but you do realize that a 36v 15ah ping is rated at 30amp max discharge? and really only 15a constant.

I disagree. A 15 Ah Ping battery can easily handle 2C (30 amps) constant. Voltage may sag a just a little, but it won't kill your battery. I wouldn't drive it much higher than that, though.

 

[gogo]

I wouldn't be surprised if your motor could draw 100 Amps max.

The first thing you should want to know is what your controller's battery current limit is. You would want to have the battery current limit dialed down to 20-30A for a 15AH Ping.

How did your NiCads die?

 

[skeetab5780]

well this probably wont answer your questions but you do realize that a 36v 15ah ping is rated at 30amp max discharge? and really only 15a constant.

I disagree. A 15 Ah Ping battery can easily handle 2C (30 amps) constant. Voltage may sag a just a little, but it won't kill your battery. I wouldn't drive it much higher than that, though.

so your disagreeing with the ping website? you also realize that this will likely cut the charge cycles in half. since the ping battery cycle life is determined off of a 1c charge/discharge

 

[skeetab5780]

i draw 30amps out of a 10ah pack all day long, im not saying it cant be done...just saying its clearly marked 1c on the website

 

[jimw1960]

so your disagreeing with the ping website? you also realize that this will likely cut the charge cycles in half. since the ping battery cycle life is determined off of a 1c charge/discharge

No, not disagreeing with the Ping website. Rather, I am agreeing with it. This quote is directly form the website page for the 36v15ah battery:

Max Continuous Discharging Amperage: 30 Amps
Maximum Discharging Current: 60 Amps

The early Pings were only rated 1C but he has been using the 2C batteries for a few years now.

 

[cgbjake]

I have an inline fuse on this rated for 40A. Just recently I was riding home and poped the fuse. I thought that was odd, a slight head wind but same route. After reading on here and talking with some electricians, I realized that because the pack is on it's way out, lower voltage means higher amps and pow, blown fuse. So I got to thinking, how about putting a slow blow 20 AMP fuse in and see what I blow? I can't imagine that with a little pedaling (I rarely go with out pedaling at all, mostly putting in 20%) then I should stay in the 10-15 amp range with a few hits over.

I realize the controversy over this, so I may drop the extra $150 and get the bigger battery...meaning another almost 9 lbs and larger box to put it in...always the balance we strive for eh?

 

[cgbjake]

Oh, and the battery pack is from the Voloci that went tits up and the pack is almost 7 years old to me, no telling how old before. It has been great for me, but as noted, just is not working anymore. Hate to get rid of it, the style just fit me perfect, now I have to figure out how to mount these Ping packs...any ideas floating around out there?

 

[jtdiode]

Hello, as far as mounting the PING battery, I have the 48v 15ah battery in an Ortlieb trunk bag with the rack adapter. The battery fits perfectly in the bag with 1" thick foam from a sleeping pad under and around it. The bag is also really nice because of how easy it is to put on and off the rack, it engages the front part of the bag and there is a quick release button on the rear that holds it in place. I use mine with a TUBAS rack and the rack adapter allows me to still use panniers with the battery in place.

 

[cgbjake]

Well, got a hold of a AMP meter and did a little testing. As I said, my hub is a SRAM Dual Drive so it's a 3 speed internal. Top speed is geared to about 36. First gear with a wide open acceleration drew about 35 AMPS for about 3 seconds, but steadily went down to about 11 once it was to top speed in first, shift to second and it goes back up to the thirties but goes back down, hanging around the low 20's for a little longer. This is all on flat ground. So I'm thinking once I get to some medium hills I'll be way over my limit. Just to put this Curtis Controller in to perspective, I shifted to third and put a serious bit of throttle on it and she ramped up to 55 easily before my drive belt slipped (call it a mess up in my lathe abilities, but I call it a safety valve). So I'm pretty certain I need to go up to Ping's 20 AH and upgrade to the high AMP BMS. Always running that close or over the suggested discharge rate of these LiPo's my not be the right way to go. I'm figuring that will save my batteries and give me a little more distance at the same time. I'm thinking it's worth the extra $150 if your already in for $540. Any additional thoughts???

 

[jimw1960]

Unless you also need the extra amp-hours (and weight) to extend your range, you might consider spending the extra cash to get a lower amp-hour battery with higher rated cells, like Headway or A123 (assuming you want to stick with lifepo4). Cell_man was building A123 packs for a fair price, though I haven't heard much from him lately. With a 10Ah A123 battery, you could hit that throttle as hard as you like and it will deliver the amps--probably your motor wires would melt before it hurt the battery.

 

[cgbjake]

Good point Jim, I'll research that...but the extra range really appeals to me to. I may be putting this into a hub motor soon or a brushless motor for a real cruiser so I'm thinking the extra range is looking attractive.

 

[amberwolf]

Depending on the Curtis controller model, that 250A it's rated for may well be for minutes at a time, and probably doesnt' actually have any internal limiting of current (my 1231C doesn't really). So unless you use somethign else to limit current draw externally, like the Cycle Analyst via throttle-control, you could either burn up the motor or damage whatever battery you have, once you reach road conditions (like hills) that cause the motor to slow down and draw more current for sustained periods while you're still trying to hold speed up with your throttle.

You can also limit current manually, by keeping a meter inline with your battery, and watching that it never goes over a certain amount for more than a certain amount of time, and throttling down if it does, but that can get distracting in traffic, sometimes dangerously so.

If the pack BMS is designed iwth a current limit in it, most likely what it will do in response to a sustained overcurrent is to shut down all power from it, at least until the overcurrent goes away (and/or a thermal limit that has been reached then drops below the limit). But some BMSs may not actively cut the current, but simply blow the output FETs if the ratings are exceeded, depending on their design. I think the Ping is the former type.

 

[neptronix]

re pings..

The cycle life you see is quoted at a lower than 1C rate.
If you run them at 2C constant for their lives they will not last nearly as long.

Over 1C, sag is fairly bad.
If you want to get the claimed life, or anywhere near it, and decent performance, you need to size the ping according to the 1C rate.

I wonder why a "800 watt" scooter has a 250 amp curtis controller in it?
An electric motor will draw all the current it needs at startup, this can draw an extremely large spike of power.
If that number is anywhere in the 100's, no ping battery will provide this level of power. The BMS will be maxed out and not provide power. It will studder, or just not run.

I think a ping for this application is not suitable, you need something as hardy as the original nicads.

As to what your scooter actually draws, you're going to need a current metering device inbetween the battery and controller. That is the only way you can know.

 

[parabellum]

Or just get lipos from Hobby King. They will probably not last for 7 years, but you will love the low weight and high performance! Only issue, you will soon be looking for more powerful motor after you burn this one.

 

[cgbjake]

Well, I'm rethinking by whole project. I put that big controller on there because I used to run SLA batteries and the Hawkers could handle extreme AMP draw. These did really well too but now I'm concerned. I'm thinking I need to get a new controller, but my knowledge of these things are not really good, can anyone recommend a decent controller that is not designed specifically for the brushless motor? I'm almost certain there is a big difference but I can't find any good Non-Brushless ones.

Then my second guessing is causing me to think about getting a hub motor and upgrading to 48V. My goal is to have a real commuter, but one that will just be rock solid and not have to worry about anything but remembering to plug it in. Seems hubs are the way to go, but my current system is pretty flawless if I could just replace my Batts with out blowing them up.

So I'm confused, scared and frustrated so I'm taking a step back and waiting for some good thinking advise from the people on here. Anybody have some good ideas?