Advice on drop-in replacement for SLA 12V?

[DomenicDenicola]

Hi there,

I'm very new to this. I took apart my electric skateboard (cheap model that seems to be sold only on eBay) when it stopped working, and with the help of an electrical engineering major in my dorm figured out that the problem is with the batteries. Specifically, if you charge them then they will put out the desired 24V (there are two 12V in series), but if I turn on the skateboard's lights, the batteries will almost immediately be expended. I've replaced the charger and we also tested the board with a combination of AA and 9V batteries, so we're pretty sure the issue is that the batteries are bad. Which leads me here...

Basically, I need to get a replacement. But I don't know where to start. It needs to work with the same charger---I'd rather just buy a new skateboard than start ripping out and replacing _all_ the different pieces. But I don't know how much I am constrained. The battery specs are, apparently:

• Sealed lead-acid battery
• CB4.5-12 (12V4.5AH/20HR)
• constant voltage/charge
• cycle use 14.0-15.0V
• standby use: 13.5-13.8V
• initial current: less than 1.35A

So how can I replace these? Should I just look for a drop-in replacement of exactly that type, and presumably it'll work with my existing charger? Or should I go for a better kind of battery (lithium-ion or nickel-cadmium, I guess)? How expensive would this be, and where would I buy these?

Thanks; hope you can help.

 

[Link]

Ah, lucky you are! I happen to have an identical skateboard. G-1, right? I modded mine. It now runs 48V with a throttle (which means twice the speed yours goes 8)). Fun, but the front wheels are getting trashed. I need to find better ones for cheap...

Anyway: You can got them in quite a few places if you search the net. They're occasionally on eBay, but be wary of those though. Make sure you ask if they're new (NOT new old-stock; I basically wasted $60 on batts that way :?). If you have a local electronics shop, you might check there. I think Fry's carries them. Mind you, though. That the batts will run you about $25 a piece. You could almost get a new board for that.

You might want to look at other chemistries if you have other electric transportation. You can fit much more in the same space, and they'll last longer. But if you don't I'd just get a new one. I'm pretty sure these are a discontinued product and are being sold off by someone who bought the warehouse inventory. We're getting them for less than it costs to make them.

You might want to look into overvolting the thing, too. The stock controller will handle a 36V pack, but you'll either have to mount it externally (what I did) or get a different chemistry (NiMH, NiCd, LiFePO4) that doesn't take up any more space.

Few notes: The batteries are only giving you about 2.7Ah of power (due to Peukert losses). A 5Ah battery of another chemistry would likely double your range. I believe the controller is limited to 10 or 15A (the fuse is rated at 20A). If you overvolt, be wary of the belt. I took mine out in the rain once at 36V and the slippage destroyed it. The throttle takes a hall effect throttle. The motor is rated for 200W, but I have run it at peaks of 1300W when I ran it at 48V, so don't worry about it too much at less than that.

I find it odd that it just suddenly stopped working. That's very unusual for a battery. Typical wear is shown as a gradual loss in capacity throughout its lifetime. Yet you say it works on other batteries. Interesting. How long have you had the skateboard?

 

[DomenicDenicola]

Thanks Link! Yeah, it's the G-1. And I do agree, they probably are being sold off by someone who bought the warehouse stock.

It sounds like there are a lot of options here, but I don't really understand how it all fits together. What do higher volts, or higher Ah, translate to in real terms? It sounds like volts = speed and Ah = range? When you say $25 apiece, that's per 12V, right? (So $50 total.) And if I were to get something of a different chemistry, what price range are we talking for those, and what would I need to do to make them work?

I'd love to extend the range; the speed isn't too important for me though (although it might be fun to get it higher). Lowering the weight would be cool too. But also, it sounds like there are some limitations on what the rest of the board can take, like you were saying with the wheels and belt. I'd rather avoid too many problems if possible...

(On a side note, any tips on reducing the noise level created by moving over sidewalks, cobblestones, etc.? I was looking for rubber wheels, but nobody seems to have any, especially not ones that fit this board.)

And yeah, it is strange how they just suddenly stopped working. The only possible cause I can think is that it had rained earlier today, and the pavement was pretty wet. But I wasn't sliding through puddles or anything, and it wasn't actually raining, so it seems unlikely...

Thanks so much!

 

[kbarrett]

Sounds like your controller may have shorted out due to weather.

Get a cheap ratshack multimeter and test your batts ... if they show anywhere near 24V, but won't start the controller and motor up with zero load, then replacing the batts may not fix the problem.

 

[fechter]

The connection between the batteries could have gone bad. Check the connectors. I have also seen batteries that had a conductor break internally. Under no load, like a voltmeter, they would show normal voltage, but would dive to near zero under load. You could load test them with a light bulb from a car. Put the bulb across each battery and see if it lights up. A big bulb, like a headlight, is best.

 

[Mathurin]

Wish these things were legal here

 

[Link]

Wish these things were legal here

*img snip*

They're not, uh, exactly legal here either; some crap about an emergency clause or something that was started back in like the eighties. Hippies probably had something to do with both sides of that :?.

And pretty much, yah. :wink:

It sounds like there are a lot of options here, but I don't really understand how it all fits together. What do higher volts, or higher Ah, translate to in real terms? It sounds like volts = speed and Ah = range? When you say $25 apiece, that's per 12V, right? (So $50 total.)

Mmhmm.

And if I were to get something of a different chemistry, what price range are we talking for those, and what would I need to do to make them work?

Substantially more. The cheapest you can get a lithium pack is from PingPing on eBay. $250 shipped for a 24V 10Ah battery (which means same speed, nearly quadruple range). I've only priced one brand of NiMH (Tenergy D cells), and came up with something like $150 for a pack that would BARELY work. Plus I'd have to make the pack out of the cells myself.

Compared to the cost of the board itself, that's a very significant investment. If you were prepared to spend that kind of dough on batteries, I'd recommend you get a higher quality board.

I'd love to extend the range; the speed isn't too important for me though (although it might be fun to get it higher).

Range is always an issue :?.

Overvolting is fun. The stock 24V is fun for a while, but I can easily run faster than the thing. 36V is a blast. It's an awesome improvement (though will wear the front wheels noticeably faster). 48V is technically doable (with a different controller and a throttle), but absolutely destroys the wheels. Mine have been ground flat in a dozen rides. The suspension is questionable at these speeds, too (should be over 25mph).

Lowering the weight would be cool too.

You probably won't notice that much of a difference in weight; the entire board is steel, and the batteries make up a little less than half of the total weight.

But also, it sounds like there are some limitations on what the rest of the board can take, like you were saying with the wheels and belt. I'd rather avoid too many problems if possible...

Indeed. I suspect the suspension could be improved dramatically with better wheels (soft rubber or semi-pneumatic). Not much you can do about the belt, save for swap it out for something better.

(On a side note, any tips on reducing the noise level created by moving over sidewalks, cobblestones, etc.? I was looking for rubber wheels, but nobody seems to have any, especially not ones that fit this board.)

Replace the front wheels. They're my number 1 complaint. Unfortunately, they also seem to be impossible to replace. They're kick scooter wheels (think Razor), and I've never seen that particular size in rubber or semi-pneumatic. I've never seen a similar rear wheel in my life, so that will definately prove a problem when it wears out. The front wheels are much noisier than that one, so that doesn't really need replacing till then.

And yeah, it is strange how they just suddenly stopped working. The only possible cause I can think is that it had rained earlier today, and the pavement was pretty wet. But I wasn't sliding through puddles or anything, and it wasn't actually raining, so it seems unlikely...

Sounds like your controller may have shorted out due to weather.

Highly unlikely. The controller is not watertight, strictly speaking, but I'm sure it could handle anything short of being completely submerged. The ride I took out in the rain (the one where I stripped the belt) was AFTER I removed the controller from inside the skateboard to make room for the additional battery. It was splashed on by the front wheels in puddles and sprayed on constantly by the rear, but was bone dry when I took it apart later to check it out, with no residue that would indicate that water had ever gotten into the thing.

Plus, you say it worked with different batts. I'm assuming this was tried with the controller in place?

The connection between the batteries could have gone bad. Check the connectors. I have also seen batteries that had a conductor break internally. Under no load, like a voltmeter, they would show normal voltage, but would dive to near zero under load. You could load test them with a light bulb from a car. Put the bulb across each battery and see if it lights up. A big bulb, like a headlight, is best.

Ah, another brilliant hypothesis from our resident wizard Fechter :wink:.

Considering the kind of shock this thing puts on the batteries (Domenic can attest that it's far from a smooth ride), that seems possible. Probable, even. A load test like Fechter describes would tell you more definately.

 

[DomenicDenicola]

So I ordered another one from eBay, just to avoid the hassle. I have an extra chassis now, in any case . I'll see if I can do a load test like you were saying; I'll need to wait for all the EE majors to get back from break with their voltmeters and stuff.

Sounds like my best long term plan might be a better board though, so maybe if this next one doesn't last me forever I'll go that route instead. But as for modding...

How would I overvolt, and would it have any effect on range? Is this something I can reverse if I get scared of the wheels dying forever? (As you say, hard to replace.)

Are there any mods to extend the range, or is upgrading the batteries really the only option?

How would I go about finding a better belt? I've noticed them dying pretty fast, and although I guess I have two spares with no wear and one with little wear, it does make me think it could be better. (It's also annoying when the belt gets too lose and starts screwing itself over... have to spend some time retightening the screws and such, bleh.)

Wheel mods though would be great... how exact do you think they would have to be? I mean, I kinda feel like if I just got something with the appropriate axle-size, and large enough to keep it clear off the ground, it should work... maybe...? Another thought I was having was some kind of attempt to "coat" the wheels with rubber (or something)... I have no idea how I would really do that, but in theory it seems like it might be doable if one was careful.

 

[Link]

So I ordered another one from eBay, just to avoid the hassle. I have an extra chassis now, in any case . I'll see if I can do a load test like you were saying; I'll need to wait for all the EE majors to get back from break with their voltmeters and stuff.

Good idea, actually. I ended up doing the same thing. One to ride, one to screw with. Unfortunately, I ended up with none to ride, two to screw with .

LOL, when Barrett said get a cheap voltmeter, my cheap side said, "Naw, borrow the engineers'".

Sounds like my best long term plan might be a better board though, so maybe if this next one doesn't last me forever I'll go that route instead. But as for modding...

How would I overvolt, and would it have any effect on range? Is this something I can reverse if I get scared of the wheels dying forever? (As you say, hard to replace.)

You stick 3 12V batteries in series and hook that up to the controller. You need some spade connectors and soldering skillz, but the EEs should be glad to help (I hear beer helps grease the gears [possibly literally and figuratively, in this case {also: LOL that rhymed}]). The existing connections are a pain in the ass to remove, though. Definitely get help if you haven't soldered before. I've been into this sort of thing for a while, and I still burned the plastic a little while messing with the connections.

Range would probably be about the same. The extra battery provides more capacity, but that's offset by the extra power requirement.

It's reversable. Just take the extra battery out of the string.

Are there any mods to extend the range, or is upgrading the batteries really the only option?

Not really. I did strap a monstrous 18Ah pack to the outside of the thing with a belt once, but that didn't last long as it looked kinda, how do you say, "douchebaggy"?

How would I go about finding a better belt? I've noticed them dying pretty fast, and although I guess I have two spares with no wear and one with little wear, it does make me think it could be better. (It's also annoying when the belt gets too lose and starts screwing itself over... have to spend some time retightening the screws and such, bleh.)

I was afraid you'd ask that. I don't really know, actually. IMO, the best thing to do would be to replace the belt AND cogs with something more robust, but since the back wheel IS the cog, that's not really doable. There perhaps exists a stronger belt made by someone other than Kaina, but I had a hard enough time finding even an exact replacement. :?

Wheel mods though would be great... how exact do you think they would have to be? I mean, I kinda feel like if I just got something with the appropriate axle-size, and large enough to keep it clear off the ground, it should work... maybe...?

Let me put it this way: The way I intend to replace the wheels is with semi-pneumatic or rubber caster/scooter/whatever wheels that just happen to be a similar size to the existing ones and that either have compatible bearings or can be fitted with them. I'm still casually looking, though.

Another thought I was having was some kind of attempt to "coat" the wheels with rubber (or something)... I have no idea how I would really do that, but in theory it seems like it might be doable if one was careful.

Such a thing would either require that the wheels be mechanically altered so that the rubber could be securely affixed to the wheels (but then why not just make new wheels on the existing hubs, then?) or a comprehensive knowledge of plastics and rubbers so that you could pick the right rubber to both be soft enough to dampen whatever shock it might encounter, yet still bond with the polyurethane (I think they're polyurethane) wheels.

So, yeah. Doable, but impractical.