Is 2s1p for SLA battery a bad idea?

I’ve searched and haven’t found anything much on this, so maybe it is a bad idea. I have seen sellers dealing lithium ion batteries set up like this, so maybe it’s not too bad of an idea.

I have 3 identical Sla batteries. They are all 12v 8ah. Their ages are different and have come from different locations. They were all used in identical devices.

I can only fit 3 SLA batteries in my scooter. I saw a diagram

This one



That would make the 2 in parallel a different size battery from the one being added in series. It would be a 12v 16ah battery in series with a 12v 8ah battery, right? Would discharging be an issue? I charge these batteries separately. I’d like to have the 24v 16ah source that this arrangement could give, but I don’t want it if it is a bad idea in the long run. Any input is appreciated. Thank you.

A few notes:

2s1p means you have only two "cells" (or two batteries, in your case, each with six cells inside the casings that can't be individually accessed). They are connected only in series, with no parallel connections at all.

The diagram you show is not labellable in this fashion; it would be a 1s2p in series with a 1s1p, if you had to try to label it this way.



As for adding that third battery, there's no point in putting the two 8Ah in parallel, if they are going to be then put in series with a third 8Ah. Because there's no fourth 8Ah in parallel with it, the entire pack of batteries is limited to just the 8Ah capacity of that 1p, and limited to it's current delivery ability as well.

You get nothing but extra weight out of the second 8Ah in the 1s2p section. (technically it reduces the loading on the paralleled pair, so you might get a bit more capacity out of them, but since you still have the same loading on the unparalelled single battery, and the same capacity, you can't *use* the extra capacity or capability of the paralleled set.)

So its' still only a 24v 8Ah battery, not 24v 16Ah.

It requires 4x 12v 8Ah batteries wired as 2s2p to make a 24v 16Ah pack.


If you can only fit 3 SLA in there, and you want more capacity, your best bet is to find (or build) a lithium pack that is the same shape and size as those three SLA, since it would by it's nature have greater usable capacity than SLA , even if it had no greater Ah rating, and being half again bigger than the two SLA you can actually use, it would have that much greater capacity. You just have to make sure it is made of cells capable of supplying the current (A) that your scooter requires (typically listed on the controller as a current limit; usually best to get a battery at least 25-50% more capable than required so ti can still do it as it ages).


Alternately, you could put all three in series, so that even though you don't get more Ah, you do get more Wh, which is also capacity, because it's 12v x 8Ah x 3, instead of 12v x 8Ah x 2.

To do that you must make sure your controller is capable of handling that voltage (42V+ fully charged), or it may fail. (if it's a brushed controller it may well fail stuck on, so the motor won't shut off until you unplug the battery!)

Note also that upping the voltage ups the speed at full throttle, so you may want to be sure to reduce your throttle usage to maintain the same speed you had before, or change the gearing of the motor-to-wheel if it's a chain or belt drive to get back to the orignal speed. If not, you will probably actually get *less* range because the higher speed will take more power. Changing the gearing this way would give higher torque so it would startup from a stop (or climb hills) easier.

Thanks, Amberwolf. I did check my controller before trying these at 36v. It worked, I got a bit more speed (3mph more). I figured I'd have less range than at 24v due to the added weight and the higher wattage being outputted.

I have this controller

https://m.media-amazon.com/images/I/61YT4yVs2XL._AC_SL1001_.jpg

I assume the max current this outputs is 20A. Probably 10A continuous? I bought this for the simple fact of replacing the old throttle. The old controller had a linkage type throttle assembly. It would get stuck and I couldn't fix it. It was shit.

I'm looking at lithium batteries for the reasons you mentioned. I'm not confident in assembling a pack and don't think I'll be saving much to create this one pack. Especially if I have to buy the tools to do so. I did start collecting 18650 cells, but they are all in their own packs 2P2S. I've got 4 of them and come across these packs often. I feel I'm wasting my time collecting them, lol.

This is a scooter that I found on the side of the freeway. It was trashed. If I'm going to go with a lithium pack, I'll probably upgrade to a brushless motor, but that may be a topic for another day.

This is a belt driven motor. The belt is original from 2007. I do need more torque due to the hills in my area, so maybe changing the gearing is my best option......for now

slaphappygamer said:

https://m.media-amazon.com/images/I/61YT4yVs2XL._AC_SL1001_.jpg

I assume the max current this outputs is 20A. Probably 10A continuous?

Click to expand...

SInce it doesn't say either way, then to know for sure you'd have to test using a wattmeter or ammeter (wattmeters are cheaper for the capability, by far, and useful for more things in EV-land. ).

If it is actually 20A, it's pushing those little SLA pretty hard; I would guess they sag in voltage a lot when it's at that current.

THis page
https://translateimages.site/results
using your image
https://m.media-amazon.com/images/I/61YT4yVs2XL._AC_SL1001_.jpg
says it's Rated power 500w which probably means 20A continuous current limit (500/24), but there's not enough info to know.

In my limited experience with them, brushed controllers typically use "rated" as the continous value rather than some short peak / max, while it's a tossup on brushless ones...the brushed ones are not typically smart enough to tell how long the current is at some level and then turn it down, unlike many brushless ones, so they just have a single current limit...and the really cheap brushed ones don't even have an actual current limit at all--they trust the user to not push them past their limit and blow them up :lol:

I'm not confident in assembling a pack and don't think I'll be saving much to create this one pack. Especially if I have to buy the tools to do so. I did start collecting 18650 cells, but they are all in their own packs 2P2S. I've got 4 of them and come across these packs often. I feel I'm wasting my time collecting them, lol

Click to expand...

.

If they're used, and especially if they're not intended for EV purposes (high current for long periods), then they're not much good for a limited-size pack, because to use them without overstressing them*** you have to parallel a lot of them, and the pack gets big and heavy real fast.

*** pulling more current than a cell can handle causes a lot of voltage drop under load, which means you get less power (watts) out of the pack, so if the upgrade is to get more power it doesn't actually do that (and may even be worse than the SLA). It also means you get less capacity because like the SLA more power gets wasted as heat instead of going to the motor, so you get less range. It also makes the cells last for less lifetime, because the harder they are used, the more they are "damaged" or "worn" each usage.

Tools to build and test a pack from salvaged cells can end up costing more than just buying a pack new, depending on th the cost of the actual cells--if they're all free, it might be cheaper...but most of the time there's a reason the cells were free.

Places like batteryhookup sometimes have used packs that may be adaptable to a new usage that's less hard on them than the original usage.. Some of them are easy enough to physically reconfigure by cutting interconnects, then soldering just the interconnects back together (with thick wires, if necessary) without heating up the cells. They don't often have usable BMS with them, and a decent one is probably going to cost $40 and up, depending on functions required, etc.

This is a scooter that I found on the side of the freeway. It was trashed. If I'm going to go with a lithium pack, I'll probably upgrade to a brushless motor, but that may be a topic for another day.

Click to expand...

If you do, I'd recommend poking around the various threads about such conversions; there have been a number of good ones over the years. Since yours is belt driven you can probably take the drive sprocket off the present motor and move it to the new one, so you can keep the drive system and just switch to the potentially more efficient motor.

This is a belt driven motor. The belt is original from 2007. I do need more torque due to the hills in my area, so maybe changing the gearing is my best option......for now

Click to expand...

Gearing is an "easy" way to get more torque...but it is at the cost of speed, proportionally. Making the drive gear bigger makes the system faster. Making the driven gear bigger makes the system more torquey. (just like shifting gears on a bicycle).

A coulumb meter is what I got. I saw you recommend the circular version. I got the rectangle version.

https://www.aliexpress.com/item/3256804535264029.html?spm=a2g0o.productlist.0.0.3a371a9aaH1tMO&algo_pvid=f42f8e7f-06b6-49b9-88e5-4bbd6108b6e1&algo_exp_id=f42f8e7f-06b6-49b9-88e5-4bbd6108b6e1-1&pdp_ext_f=%7B%22sku_id%22%3A%2212000030229858219%22%7D&pdp_npi=2%40dis%21USD%2151.12%2138.34%21%21%21%21%21%40210318c216639045998862178eadab%2112000030229858219%21sea&curPageLogUid=IMlMqXQG4wp8

I saw 6.8 amps at max throttle with no load. I'll see what it is under load this weekend.

Thanks for the translation link, the internet is a really big area and I never knew that this even existed. That'll come in handy, bookmarked!

I'll be careful not to push this controller too hard. It was really cheap at $10. Yes, I went for the cheapest one I could find.

I'm realizing that I am wasting my time collecting cells that I'll never use. They were used in modems. Modems that are being replaced by a new generation.

Even though this scooter was free, I really want to do my best to keep for a while. So I'll find a way to install the coulumb meter on the handlebars. I didn't even know they existed until i read a post of yours.

I found out too, as I priced everything. It was almost $400. I may as well put good money in a good pack and let a pro do it. Also safer for me. I don't have steady enough hands for that sensitive type of work. I can get a 24v20ah with 21700 samsung 50e cells for that price and it's the right size to fit my scooters deck. If I go that route, and start dumping big money in this, maybe it's best to get a 36v battery and a brushless motor kit.

I'll keep watch at batteryhookups. I don't mind having a used pack, as long as it has brand name cells.

I've been reading some of those threads about scooter conversions. I was trying to find out more about removing the sprocket on the motor to know if I can maybe change to a chain. Maybe I can. Since I got the scooter for free, I really just want to learn from it. I don't mind if it's down for a while, or even if it breaks. I don't use it to get to work, or anything important.

Slaphappy you first will not work don't try it.
Like up series of batteries. The basics.

Thanks. I won’t be trying this as it has been deemed a bad idea.

slaphappygamer said:

A coulumb meter is what I got. I saw you recommend the circular version.

Click to expand...

? I don't remember a circular version, but I guess if it was long enough ago I might not.

But pretty much any of them, assuming they're made correctly, and calibratable to the shunt used on them, will do a good enough job for guesstimations, which is all that's really needed most of the time.

I saw 6.8 amps at max throttle with no load. I'll see what it is under load this weekend.

Click to expand...

That's a pretty high no-load current for such a small motor/controller. I'd expect something closer to an amp or two at most, probably less for what you've got.

Is there some physical drag on the system?

Another possibility is that the meter is not calibrated to it's shunt. I glanced thru the linked page but didn't see anything about doing that. Hopefuly it comes with a paper manual that shows how to change the shunt resistance setting in the meter, and the shunt is marked with it's tested resistance.

Also, if you have the high-current version of the meter, it will generally be less able to precisely measure smaller currents. The lower current version is more likely to be able to read smaller currents.

Thanks for the translation link, the internet is a really big area and I never knew that this even existed. That'll come in handy, bookmarked!

Click to expand...

THere are also apps for android and ios that let you use the device camera to do live translations, but they dont' help much with webpages (unless you point it at a screen of another device showing the page, not as easy as directly doing it with that linked page).

I'm realizing that I am wasting my time collecting cells that I'll never use. They were used in modems. Modems that are being replaced by a new generation.

Click to expand...

THere've been some threads about ex-modem cells to build a pack from. I don't recall the results, but the cells would be pretty low-capability, current-wise, almost certainly sacrificing that for capacity (as they wouldnt' need high currents to run a modem).
These threads turned up in a quick search
https://endless-sphere.com/forums/viewtopic.php?f=2&t=104471
https://endless-sphere.com/forums/viewtopic.php?f=14&t=96528
but not sure there's much useful actual results there.

So I'll find a way to install the coulumb meter on the handlebars. I didn't even know they existed until i read a post of yours.

Click to expand...

FWIW, if you ever go looking for a different one, you'll see them more commonly called wattmeters though that's not all that they do, and coulomb meter is just as applicable. Some examples of RC-style wattmeters
https://www.google.com/search?q=rc+wattmeter&tbm=isch
more widely varied results, most of which aren't usable for ebikes/scooters
https://www.amazon.com/s?k=wattmeter&ref=nb_sb_noss
.

I've been reading some of those threads about scooter conversions. I was trying to find out more about removing the sprocket on the motor to know if I can maybe change to a chain.

Click to expand...

Keep in mind a chain will probably be noisier, especially with the tiny sprockets usually used on these motors.

If the belt works fine and doesn't cause you problems, and you can get sprockets of the right size on whichever end you need to change for torque/speed, and a belt of the right length, then there's not really a reason to change to chain.

(my motto in experimenting has often been "if it's not broken, upgrade it till it is", but that is more fun than helpful....)

I calibrated my meter according to the documentation. Under no load, I’m pulling 2-3 amps. Under load, 180lbs total weight, it’s more 15-20 amps. I saw 25 at its peak, with a slight incline. Poor SLA’s.

Thanks for the heads up about the chain. The brushed motor is loud enough. Lol

I did run this at 36v (3 SLA in series). Motor almost pulled 1000w. Yes, almost 30AMPS! The motor got hot quickly. Almost 100f. I won’t be doing that anymore. Lots of pep, though. A 36v scooter is not for me.

With the meter in place, I can see now why my batteries went to about 50% after 20 minutes of riding. Just about 3 miles.

Sounds like the controller does not actually monitor or limit current (common with cheap brushed controllers). Any current limit on it's label or specs is there to tell the *user* not to exceed it. :lol:

We've seen so many of them just blow up from this on various brushed-motor scooters, bikes, toys, etc., when it is overloaded.

It's funny, because there's really "nothing" to adding current limiting to the controller even in a cheap design--it doesnt' even require a shunt, because it could measure the voltage drop across the FETs in the bottom half of the bridge easily enough--as long as the FETs are always the same kind used so their RDSon is about the same, and the design can be done around that.

Oh wow! Ok, thanks! I’ll be sure to be careful with the throttle. I’ll also have to keep the coulomb meter on it, to keep a close watch.