My first e-bike project log named: "P.O.S."

[def215]

i had a question. would anyone know what the full charge of an SLA battery pack is? its 24 volts, hot off the charger, its about 26 volts on the nose. even though its fully charged, i get the yellow light under full throttle. could it just be pulling too much current also because i did do the shunt mod to my controller.

 

[enoob]

id suspect your drawing more amps than the cold sla's can keep up with .

once you let of the throttle does the light go out ? if so thats a pretty good hint your asking more than they are capable of . good news is if and when you upgrade the batts there is definitely performance to be gained .

 

[def215]

you pretty much hit the nail on the head with that explanation, enoob. it only happens under full throttle. i go half throttle, the light stays green. anything above that, it goes into yellow. ill take out the shunt mod that i did and see what happens.

so today i had some great weather here, around 50 degrees(and its winter here) so i took it out for testing. everything seemed great after i rebuilt my chain diverter after it crapped out, and then this happens:

my tether gets caught in my rear tire and brakes and gets severed like string

what my odometer reads before something went wrong...i guess thats why im running it through its paces...lol

on a good note, i think this is my top speed i clocked before i broke it...lol
i am definitely pleased with my bike so far except for this incident that just happened.

 

[def215]

ok. let me shoot out another question. at this point in my project, i encountered a dilemma. right now im not sure im getting max efficiency levels or my batteries are completely trashed. but, i am only pushing 250watts, all of the electronics came from an electric scooter, and im not sure if im geared correctly. so my questions that i have are this:

-on my last test run, i fully topped off my batteries, which are 2 12volt 7aH SLA's i believe, and i only got about 3 miles out of it. could the batteries be trashed and sulfated to death?
-also im not sure if im geared correctly. im geared at 6.5:1 ratio, 8 tooth on the motor, 52 on the rear wheel. does this gear ratio sound correct to anyone, or do i need a higher ratio?
-i am not sure if im getting maximum efficiency out of this setup. if i read correctly, if i have the motor rev higher close to its max rpm, it is more efficient. the max rpm of the motor that im running is 3000 rpm. im getting about 1700 rpm at the top speed unassisted, which is around 15 to 16 mph. could this be affecting its efficiency.

right now im really looking into rewinding my motor to get some more torque out of it. right now im thinking this thing is seriously underpowered for my weight, which is 115 lbs. if any one can give me an answer, its greatly appreciated.

TIA

 

[dequinox]

I won't comment on the rewind as I know nothing about it.

Efficiency is hard to measure unless you have something that can track the current you are using.

We usually use something like a watts up meter or a Cycle Analyst, there is a "Turnigy Power Analyzer" available from hobbyking.com. It's only $25 and the other two are much more expensive. I wouldn't rebuild myself until I knew what kind of efficiency I was getting for sure.

For that you would measure the total Amp-hours used (Ah on your meter) and multiply it by the average (I think you can use the nominal...that is to say 24v vs 25.4-23.9 or something...) voltage of your system. You take that figure and divide it by the total distance traveled in Watt-hours/mi. Personally I've got a bit of an old-school setup. An analog Ammeter and my bike computer. I keep an eye on my amps and try to keep the bike at a steady speed on a flat. I use that draw, note the speed, and multiply it by the time I would ride the bike. I usually use an hour to keep the calculation simple:
So riding my bike at 18mph, using 15amps, I would go about 18 miles in 1 hour (On a perfect flat, no wind, VERY steady throttle hand). I extrapolate that and do my calculation for a 24v system:

(18A*1hr*24v)/18mi=24W*hr/mi.

I would have power usage rate of 24 watt-hours per mile. Keep in mind that's a power usage rate and NOT an efficiency rate. You can compare it to other folk's usage rates to determine about where you fall on the efficiency chart though. Now I have no doubt my usage fluctuates from that value depending on the hills, stop and go traffic, or other factors such as, and especially, wind resistance.

Typically I can get about 7-8 miles with light pedaling out of my 12ah SLA pack (also 24v) before the performance starts to drop off. So at 7ah I am not surprised you are getting only 3 miles. If they are not new batteries they will have a slightly lower capacity than they would new. Out of a 7ah battery...especially SLA...usually you could expect from 4-5 miles.

The thing is that SLAs don't give their full capacity on a deep cycle like lithium does. They are a great performer for a while, they are cheap and easy to get...but they are bulky heavy and crap out after a year (just about no exceptions if you use it daily).

*EDIT

I noted that you are "pushing 250watts" so I guess you do have a way of measuring?

And as to the gear ratio, all I can tell you is there is a sweet spot for efficiency on every motor...but I have no idea what it is for your particular motor. It is somewhere between the efficiency peak and the performance peak (that is max eff. and max torque) on a graph that plots torque and efficiency over RPM. I think you are probably fine with the ratio you have... mine is variable...but I'll dig it up if you want. I think I wrote the calculation down somewhere...

 

[def215]

thanks dequinox,
the numbers you gave me are reassuring. it last 3 miles but ive been running it flat out at full throttle. considering that, i tried to plug in some numbers into the equation you gave me. my motor is a 250 watt motor so i just went with the amperage calculation the motor would give me at 250 watts, which is 10.4 amps. it didnt last anywhere near an hour . i think it lasted only about 15 minutes flat out, no pedaling, just motor working by itself.

so this is what i came up with with all of the numbers:
((10.4A)(1 hr)(24v))/3mi=83.2wh/hr

Does that calculation sound correct? . this would just be an average of what i think my power usage numbers look like. it seems a little high. i wouldnt really know until i get a real CA, or when im really able to find out my amperage when im riding. ill try to figure out some of those numbers when i ride again.

i have experience with motor rewinding because i have done it with a few of my RC cars. but i dont really want to butcher a perfectly running motor yet...lol. so ill put that idea on the back burner for now. i think im due for a battery upgrade anyways. im not sure what the previous owner of all of these electronics i had did to them when they owned it.

 

[def215]

so today i finally took it for its maiden voyage(well the first ride that i ever took that wasnt a test run). i can honestly say that it is in working order. nothing fell apart, broke, went up in flames, or something bad happen to it, yet *knock on wood*. the combination of my 3-speed hub for the pedals, and the direct drive of the motor really goes together smoothly. i gotta say, it is pretty fun riding this thing around, the only thing is that it was cold(about 37F). heres a pic that i took for fun. i went to home depot to ironically buy chain and a lock for my bike...lol.

its locked, but with a crappy lock that you could probably cut with a pair of wire cutters...lol. i was sweating the whole time i was in the store.
also heres a vid of me riding it home. close to the end of the video, the batteries started dying. darn SLA's...lol
[youtube]ijhGQZkxZPE[/youtube]
theres snow expected in my neck of the woods, and i wanna take it out after a nice coating of the white stuff comes down...

 

[amberwolf]

Missed this thread before, but a few things:

To find out the right gearing for what that motor was "designed" for, look at the scooter it came from. I had a trashed ScootNGo I took apart, which had a 24V 250W Unite motor (already damaged, unfortunately), geared about 5:1 with an 11t motor end sprocket and a wheel end sprocket of 54 or so, I think it was, about a handspan across. The wheel was 8" diameter.

So in order to use the motor the way it was designed, I'd have to either use the same diameter wheel, or change the gear ratio to match a larger wheel. I always get confused with gear ratios as to whether I go up or down for things, so this could be wrong, but I think I would have needed to use a much larger wheel end sprocket to make up for the much larger wheel, to keep the motor using the same power and at the same wheel speed. (might be needing a *smaller* wheel sprocket instead).

After you have figured out what size sprocket to use at the rear wheel to make it spin the *same* speed as the original wheel, then if you want the motor to turn the wheel faster than it would have turned the original wheel, you'd use a smaller wheel sprocket than that, or a larger motor sprocket, or both. This results in less torque, but more motor loading and possibly overheating at lower speeds but high throttle (like startup from a complete stop). Pretty sure this is what finally smoked the little one I had.

If you want the motor to turn the wheel slower than the original wheel, use a larger wheel sprocket or smaller motor sprocket, or both. This results in more torque, but also less motor loading at lower speeds.


Regarding the SLA, are those the little 12Ah? or are they smaller, the 7Ah? Basically if you are drawing 10A then yeah, they won't last long on each ride. Getting down to 50% DOD (a good safe cutoff) is only going to take about 15 minutes or less. Even if you go to 80% DOD (shortening their life significantly, most likely) you'll only get another few minutes at best, in my experiences with them on DayGlo Avenger's radiator fan motor setup.

In your efficiency measurements, your motor is rated as capable of dissipating 250W of power. That doesnt' mean that 10.4A is the limit of the current it would draw; or even the average. So that current could be significantly different from the actual one. Do you have access to at least one of those cheap Harbor Freight meters? They can take 10A for "30 seconds" without melting the shunt off the board (which can be put back on, don't worry...ask me how I know ), and higher currents for shorter times. You could zip tie it to the top tube, go to an empty parking lot, and hit full throttle while watching the meter to see what current starts at and what it is at at different apparent speeds and throttle percentages.

BTW, I think you mean Wh/Mile, rather than Wh/hour.

Now, 83Wh/mile is pretty danged high, but not necessarily unexpected if the motor sucks lots of current all the time, especially if you're just letting the motor do the work and not pedalling hard enough to help it. It's worse if you also don't pedal for startups from complete stops, because it uses up a LOT of power to get that work done--more than most other times, though for a shorter amount of time. Partly it does depend on your gearing. If you optimize the gearing for speed, you're going to have a higher cost of power getting to that speed. If you optimize the gearing for torque then you may save significant power at the startup and slower parts of getting up to speed (assuming full throttle for all conditions).

 

[dequinox]

thanks dequinox,
my motor is a 250 watt motor so i just went with the amperage calculation the motor would give me at 250 watts, which is 10.4 amps. it didnt last anywhere near an hour . i think it lasted only about 15 minutes flat out, no pedaling, just motor working by itself.

so this is what i came up with with all of the numbers:
((10.4A)(1 hr)(24v))/3mi=83.2wh/hr

Does that calculation sound correct?

I would say no, it doesn't sound correct. The reason is you multiplied by an hour, and I'm sure you didn't take a whole hour to go 3 miles! If it took 15 min to go 3 miles...with your amperage value you would multiply by .25hr.

It would look like this: [(10.4A)(.25hr)(24v)]/3mi = 20.8 Wh/mi.

Look a little better than you thought? ...so yeah 20wh/mi is about 1/4th of what you thought you were using!

You must keep in mind that the motor absolutely does NOT use 250 watts all the time. That rating is the "maximum continuous" power usage your motor can handle. That, again, is a very GENERAL rating and should not be used in the calculation. Although if you are running full throttle all the time you are probably pushing 200W most of the time. To go 20mph my bike needs about 15A on a flat...so at 24v I am using 360W. My motor is "rated" at 900W...but I almost never use that much. I don't even think my batteries will give it.

For what your battery's discharge behavior, check this link out: http://www.gamewell-fci.com/datasheets/CS-2500.pdf

Its the chart on the second page on the top-left. The discharge "rates" (1C, 2C etc...) are 1 x your battery capacity. So for a 7ah cell, "1C" means 7A discharge rate. 2C would mean 14A...etc. On the bottom of the chart it shows how long the battery should last at that constant rate. Hope that helps.

Also, on a side note, your video makes the chain drive sound SUPER loud... you might want to look into what is making that noise because there could be some serious drag there robbing your efficiency.

 

[dequinox]

Do you have access to at least one of those cheap Harbor Freight meters? They can take 10A for "30 seconds" without melting the shunt off the board (which can be put back on, don't worry...ask me how I know )

An idea for you amberwolf. You could expand the capacity of your harbor freight meter by running it in parallel with a short. Measure the resistance of the meter (lol you'll probably need two meters) when it's in "10A" mode. Then wire it in parallel with a shorting wire of similar resistance. You can figure (by proof of Kirchoff's current, or node law) that the meter will read about half of the amperage you're actually drawing. I think most folks can double a number in their head easy enough... cheap solution for a digital display!

 

[def215]

I would say no, it doesn't sound correct. The reason is you multiplied by an hour, and I'm sure you didn't take a whole hour to go 3 miles! If it took 15 min to go 3 miles...with your amperage value you would multiply by .25hr.

It would look like this: [(10.4A)(.25hr)(24v)]/3mi = 20.8 Wh/mi.

Look a little better than you thought? ...so yeah 20wh/mi is about 1/4th of what you thought you were using!

ok. that looks better. i had a feeling my math was a little off. yeah, i just wanted at least a rough number so i have an idea of whats going on.

In your efficiency measurements, your motor is rated as capable of dissipating 250W of power. That doesnt' mean that 10.4A is the limit of the current it would draw; or even the average. So that current could be significantly different from the actual one. Do you have access to at least one of those cheap Harbor Freight meters? They can take 10A for "30 seconds" without melting the shunt off the board (which can be put back on, don't worry...ask me how I know ), and higher currents for shorter times. You could zip tie it to the top tube, go to an empty parking lot, and hit full throttle while watching the meter to see what current starts at and what it is at at different apparent speeds and throttle percentages.

BTW, I think you mean Wh/Mile, rather than Wh/hour.

You must keep in mind that the motor absolutely does NOT use 250 watts all the time. That rating is the "maximum continuous" power usage your motor can handle. That, again, is a very GENERAL rating and should not be used in the calculation. Although if you are running full throttle all the time you are probably pushing 200W most of the time. To go 20mph my bike needs about 15A on a flat...so at 24v I am using 360W. My motor is "rated" at 900W...but I almost never use that much. I don't even think my batteries will give it.

yeah. i wanted at least an idea of some numbers, even if it is a very rough number. ill have to try my harbor freight meter sometime but i think i blew a fuse on the 10A function. yeah, i meant Wh/mile.

so far, you guys gave me the same advice about my batteries, how only 7aH will only give me a couple miles. now the C ratings are all starting to make sense to me.

To find out the right gearing for what that motor was "designed" for, look at the scooter it came from. I had a trashed ScootNGo I took apart, which had a 24V 250W Unite motor (already damaged, unfortunately), geared about 5:1 with an 11t motor end sprocket and a wheel end sprocket of 54 or so, I think it was, about a handspan across. The wheel was 8" diameter.

So in order to use the motor the way it was designed, I'd have to either use the same diameter wheel, or change the gear ratio to match a larger wheel. I always get confused with gear ratios as to whether I go up or down for things, so this could be wrong, but I think I would have needed to use a much larger wheel end sprocket to make up for the much larger wheel, to keep the motor using the same power and at the same wheel speed. (might be needing a *smaller* wheel sprocket instead).

After you have figured out what size sprocket to use at the rear wheel to make it spin the *same* speed as the original wheel, then if you want the motor to turn the wheel faster than it would have turned the original wheel, you'd use a smaller wheel sprocket than that, or a larger motor sprocket, or both. This results in less torque, but more motor loading and possibly overheating at lower speeds but high throttle (like startup from a complete stop). Pretty sure this is what finally smoked the little one I had.

If you want the motor to turn the wheel slower than the original wheel, use a larger wheel sprocket or smaller motor sprocket, or both. This results in more torque, but also less motor loading at lower speeds.

that just made tons of sense. i think i have a similar motor to the unite 250w motor. if i remember it correctly, the person i bought my motor, controller and batteries from told me it was from a razor scooter. my bikes speed is pretty similar to the top speed of the razor scooter it came from, which is about 15mph. so i think thats correct. the speeds are pretty much closely matched.

Also, on a side note, your video makes the chain drive sound SUPER loud... you might want to look into what is making that noise because there could be some serious drag there robbing your efficiency.

yes, about that, the camera really made it sound really loud for some reason. in reality, its really not that loud. its my chain tensioner thats making the racket, but it has to stay in its position or my chain will derail and fall off. i should find another way to tension my chain but i dont have any ideas at the moment.

 

[amberwolf]

ill have to try my harbor freight meter sometime but i think i blew a fuse on the 10A function.

If it is the same "centech" meter I have (either red or yellow) as in these pics:
View attachment 2QDMotorTestSetup.JPG


Then there is no fuse on the 10A function. If it worked but then stopped, the shunt probably fell out at one end like mine:

its my chain tensioner thats making the racket, but it has to stay in its position or my chain will derail and fall off. i should find another way to tension my chain but i dont have any ideas at the moment.

The larger the tensioner wheel is in diameter, the less racket it will probably make, if that helps any.

I do not recall a pic of your tensioner in the thread but if you aren't already doing this you can make a guide wheel out of old rollerblade or skateboard wheels; they include good bearings, too, often enough. I have gotten inline skates with this type of wheel for free off Freecycle.org mailing lists locally.

There are a number of good tutorials showing how to "lathe" them out into guide wheels using just a handheld power drill to spin it. I can't recall any specific links at the moment but Sheldon Brown's site is a good place to start, or the WISIL site.

 

[def215]

yes. i have the yellow one. when i use the 10A mode, my meter heats up. i think it melted some of the plastic of the case too. i didnt know about the 10 second rule. will it read more than 10 amps when it spikes or will it just go into overload and read "1"? i never got that function to work correctly. ill try that out again when i take it out to get an official amp reading.
the reason for me not pedaling and going full throttle is that i want to push it to its breaking point to see if failure incurs. if not, i guess things are working correctly, for now...lol. i want all the bugs out of it before i use it as my commuter in the spring time.
funny that you mention about tensioners being made from roller blade wheels amberwolf. mine is a roller blade wheel cut in half and modified to fit into my frame.

its fixed in that position and its more like a chain guide like you mentioned. its on the slack side of the drive chain and it rolls smoothly so i guess thats ok, right? i think the noise is only there because it is only the plastic of the roller blade wheel too. not the prettiest thing in the world, but i got it to work

An idea for you amberwolf. You could expand the capacity of your harbor freight meter by running it in parallel with a short. Measure the resistance of the meter (lol you'll probably need two meters) when it's in "10A" mode. Then wire it in parallel with a shorting wire of similar resistance. You can figure (by proof of Kirchoff's current, or node law) that the meter will read about half of the amperage you're actually drawing. I think most folks can double a number in their head easy enough... cheap solution for a digital display!

by far the coolest thing ive heard that you could do with a multimeter. ill have to try that some time.

edit: so i hooked up the meter on my bike and i did ground to one wire of the motor and the 10A function to the other wire on the motor. is that correct or am i hooking up the meter wrong on my bike, because the bike wants to go no where when hooked up the wires.

 

[amberwolf]

yes. i have the yellow one. when i use the 10A mode, my meter heats up. i think it melted some of the plastic of the case too. i didnt know about the 10 second rule. will it read more than 10 amps when it spikes or will it just go into overload and read "1"? i never got that function to work correctly. ill try that out again when i take it out to get an official amp reading.

It'll go up to 19.99, I think, max that the display will show anyway. It'll read at least to 15A because I saw readings up to that when testing CrazyBike2 with all the meters on the toptube like you see above, on a nice hot day (the top left yellow meter had a thermal probe down to the heatsink of the controller).

Problem is, it's only meant to take 10A for 30 seconds (according to the little sheet that came in mine), and probably not frequently. So if you push it harder for longer then you heat the shunt up so much that not only will the plastic around it deform and melt, the solder on the PCB will also melt, and under vibration (like when riding), the shunt can fall out. That's what happened in those two pics showing the shunt itself in my red meter. Mine also deformed the plastic. I did know about the limitations, I just didn't really care, cuz it only cost 2 bucks and I had other better meters if I did kill it.

Fortunately it's easy to fix. I'm pretty sure that if yours stopped reading in the 10A range, it's just that the shunt fell out.

the reason for me not pedaling and going full throttle is that i want to push it to its breaking point to see if failure incurs. if not, i guess things are working correctly, for now...lol. i want all the bugs out of it before i use it as my commuter in the spring time.

That's a good method, and something I'm constantly doing with my bikes, because they're never "finished". Always something new to try. Some crazy crackpot idea when I see a new piece of junk that inspires me. :lol:

funny that you mention about tensioners being made from roller blade wheels amberwolf. mine is a roller blade wheel cut in half and modified to fit into my frame.

its fixed in that position and its more like a chain guide like you mentioned. its on the slack side of the drive chain and it rolls smoothly so i guess thats ok, right? i think the noise is only there because it is only the plastic of the roller blade wheel too. not the prettiest thing in the world, but i got it to work

Pretty is irrelevant. Working is all that matters. 8) That said, yours looks better than any of the ones I tried to make so far.

If you use as much of the urethane part (the rubbery stuff) as possible left on the wheel, then it will be MUCH quieter. If it's only the plastic part, the chain essentially just slips over it, snap-snap-snap at every link. Most of the higher-frequency noise would be dampened by the urethane, if it was still there.

edit: so i hooked up the meter on my bike and i did ground to one wire of the motor and the 10A function to the other wire on the motor. is that correct or am i hooking up the meter wrong on my bike, because the bike wants to go no where when hooked up the wires.

To use the A function on the meter, it has to be in series with what you're measuring. You will want to measure battery current rather than motor current, though, so disconnect the negative of the battery from the controller, put the meter ground/common to that wire, and the meter 10A plug to the controller's negative power input.

If it still doesn't work it means the shunt probably fell off.

 

[def215]

edit: so i hooked up the meter on my bike and i did ground to one wire of the motor and the 10A function to the other wire on the motor. is that correct or am i hooking up the meter wrong on my bike, because the bike wants to go no where when hooked up the wires.

To use the A function on the meter, it has to be in series with what you're measuring. You will want to measure battery current rather than motor current, though, so disconnect the negative of the battery from the controller, put the meter ground/common to that wire, and the meter 10A plug to the controller's negative power input.

If it still doesn't work it means the shunt probably fell off.

thanks amberwolf. i knew i was doing something wrong (im an electrician and i couldnt figure it out, howd i get my job...lol). ill hook it up that way. theres snow expected and says about a foot is gonna dump on my neck of the woods. it just sucks that i wont be able to ride tomorrow, or is it... :wink:

Pretty is irrelevant. Working is all that matters. 8) That said, yours looks better than any of the ones I tried to make so far.

If you use as much of the urethane part (the rubbery stuff) as possible left on the wheel, then it will be MUCH quieter. If it's only the plastic part, the chain essentially just slips over it, snap-snap-snap at every link. Most of the higher-frequency noise would be dampened by the urethane, if it was still there.

yeah all the urethane is gone. i guess i didnt think that one through and i screwed up on that one...lol. when this one fails, ill try to build one that still has the urethane on it to cut down some of the noise.

 

[dequinox]

I didn't realize about the 30-sec limit. You might want to limit it to 5 A just to be safe. Well less annoyed by having to shell out another $2 anyways. In the diagram below you would want two more wires connecting between the two dots by "A", the ammeter. As seen in the picture the ammeter should read about half of the real current. Drawing 10A? you would see 5A on the meter. In the case I mentioned with 2 more wires it would read 1/4th the real current. Drawing 10 A? you'd see 2.5A.

View attachment Ammeter hookup.JPG

 

[def215]

so is it just possible that i just parallel it with the connection from the battery to controller? should i also find out the resistance of the wire connecting the battery and controller?

 

[dequinox]

Find the resistance of your meter, and the resistances of the other wire between those two dots. I would definitely put it between the controller and the battery because thats where the amperage is most intense. What you're pulling out of your battery is what you're interested in right?

 

[def215]

yes. i want to know how many amps are being drawn. doesnt the cycle analysts take the readings between the battery and controller also? i found out how much resistance the segment of wire is between the two points which is 0.2 ohms, if i read correctly. now i need to find out the resistance of my meter.im finding the resistance of the 10A function, right? also,am i taking the reading off of the negative or positive side of the battery?

 

[amberwolf]

Doesn't matter which side, but I just always use the negative. Eaiser to be consistent then I know what wires go where on everything.

In theory, you should be able to just set the meter to ohms, then connect the ohms lead to the 10A lead, since it already has ground in common with ohms. But the shunt is probably way too small a resistance to measure with the meter accurately that way. Mine can't read much below 10ohms even semi-accurately. Even my old Fluke has trouble with stuff below 1.

Remember also that the meter leads have resistance that is probably higher than the shunt resistance is. Touching them together by themselves, on ohms, will tell you what the meter thinks their resistance is.

FWIW, 0.2ohms sounds high for a piece of wire that short. Probably the meter inaccuracies.

 

[def215]

ok. so earlier last week was my spring break from school, so ive decided to go riding around the city. long story short, i ended up wiping out on my bike. no real damage to my bike, just some broken pedals. but now im second guessing things. i think i *expletived* something up when i went down because my LVC on my controller seems to keep kicking in under full throttle, and it has never done that before, and thats hot off the charger. now im thinking to myself, is it possible to destroy SLA's from the shock of a crash?

i carry my batteries in a backpack and i dont remember really if i fell on them, but they have no signs of ruptures or damage anhd they still take a charge. i really dont know whats going on right now. if possible, can someone give me some insight to what is goin on? because im baffled by this(waiting for the answer to go lifepo...lol)

 

[amberwolf]

Theoretically it could be possible to damage them, but most likely only if the case is cracked open for them to leak gel.

I've had (at least twice) 17Ah AGM SLAs leap off my CrazyBike2 during systems testing and hit the pavement; once at almost 20MPH it bounced a few times before skidding another dozen or more feet and stopping. Still didn't have a problem with it, even though that's a lot of impact energy, given that the first two impacts left corner impressions in the asphalt, and scarred the outside of the case (but didn't dent or crack it).

It did teach me never to use just zipties to hold them in place, though. (Hose clamps, yes)

I'd be more likely to suspect a connection. A poor connection, or damaged solder joint or crimp will be higher resistance and thus more of a voltage drop, preventing as much voltage from reaching the controller, potentially triggering the LVC.

 

[def215]

im highly impressed at the durability of these SLA cells. after my crash, and what you said happened to your SLA when you crashed amberwolf. im really surprised they can take a beating.

so i did solve my problem with the so called problem with my batteries and LVC. it was actually my controller. earlier on when i was still experimenting with stuff before my motor rewind, i did the shunt mod for more current so i can have more "punch" off the line. little did i know that that mod would come back to bite me in the ass after i rewound my motor. so me thinking the LVC was kicking in was actually my 30 amp breaker kicking in and tripping. i feel like a total tool now that i think of it. after i unsoldered the shunt back to normal, the symptoms of the yellow light coming on at full throttle at a dead stop isnt happening anymore. i also think i can get more range out of my bike now(im guessing) i was real close to breaking my bike down or chucking it into a river because this problem was really frustrating me.

now i can have that EV grin again

my controller is limited to 29 amps. would the motor only be given the maximum amps the the controller can handle and no more(theoretically?), which is 29 amps? im just really curious to this because my 30 amp breaker kept tripping.

 

[amberwolf]

I didn't crash, just that at least a couple of times an SLA leaped off when riding, due to zip ties breaking during vibration/etc.


If a 30A breaker pops, it's getting at least 30A pulled thru it for a sustained amount of time. Exactly how long it takes to pop it at it's rating depends on the breaker's specs, but I have had little 15A and 20A breakers (out of the back of a UPS) I experimented with take over 30 seconds to pop at higher currents than they were rated for.

There will be more current pulled at the motor end than the battery end (when not at zero acceleration), and I think most motor controller current limits are probably on the battery side. So the 29A limit should keep it below the 30A breaker limit, but only at the battery side. Motor side could be many times that.

Just remember that if you're using 12Ah SLAs, they were meant to have 0.6A (600mA) pulled out over a total of 20 hours (as opposed to 12A in one hour), so if you are pulling upwards of 30A out of them for any length of time they will only give you (at a guess) 10 or 15 minutes runtime max, running them into the ground. I killed my set of 12Ah by abusing them in discharge and charge on my original DayGlo Avenger MkIb friction drive, running two 12V motors in parallel at 36V (fairly high current, dont' remember exactly how much).

 

[def215]

I didn't crash, just that at least a couple of times an SLA leaped off when riding, due to zip ties breaking during vibration/etc.

whoops. i misread that one. a 17ah battery is still a pretty hefty battery to be hitting pavement like that.

well that blows my mind. i thought the 29 amp limit was for the motor to regulate current from the batteries. guess i was wrong. i just didnt want to see that yellow light flickering when it comes hot off the charger and im trying to get it moving at full throttle anymore.