Slow acceleration?

[Pinesal]

Hi, I have one of those moped style ebikes and it's been going slow for me ever since a certain occasion. The bike can still reach top speed (20mph) but takes a long time to accelerate and slows down more on Hills than it used too.

This seemed to have happened after I changed the tire. There are a few things that accompanied this event and I will go over what I suspect the cause might be the cause and you guys can tell me if any sound plausible or can offer your own explanation.

First I rode the bike over to my dad's house and left it there for two weeks. It was never charged during this two weeks. Did I mess up the battery?

Before I took it from my dad's house, we changed the tire to one that was a little thicker and a little heavier. Did the slightly bulkier tire slow it down?

While changing the tire, we accidently mashed the cable that runs unto the motor, there was damage to the protective coil but the wires looked fine. Did I mess up these wires?

Could there be another cause?

Thanks for your time.

 

[gogo]

What was the recommended pressures for the new and old tires, and what pressures do/did you use?

And welcome to the E-S.

[EDIT] It sounds like your batteries' voltage is 'sagging', which would mean that they have either deteriorated a bit or at least one of them has. Have you checked individual voltages for each battery? Before, during charging and after they've sat for at least 24 hr. after charging would be useful measurements.

SLA in series can get out of balance when charged in series, and when one gets too far out from the rest you have to attend to it individually. AFAIK, the moped makers install 'matched' batteries from the same manufacturing batch and hope for the best. Reading the voltage during operation can give you useful information about your batteries' performance.

P.S. SLA benefit from existing at as high a charge as you can manage, which means never leaving them partially discharged if you can avoid it.

 

[Pinesal]

The tires were the same size and pressure.

Ok so the batteries are the likely culprit. They are indeed sla which I forgot to mention before. I will try to look at each battery and see if I can get them to perform better.

I am toying with the idea of upgrading to lithium batteries but I have a question about that. My bike currently uses four 12v 20 ah sla batteries (48v). Am I supposed to replace it with four 12v 20ah lithium batteries? Or a single 48v 20ah battery?

 

[gogo]

I am toying with the idea of upgrading to lithium batteries but I have a question about that. My bike currently uses four 12v 20 ah sla batteries (48v). Am I supposed to replace it with four 12v 20ah lithium batteries? Or a single 48v 20ah battery?

If there is nothing tapping off a single 12V battery, then you only need to think in terms of total battery (48V XXAH). Its always good to get the schematic if you can.

Your controller specifications will be important in determining a suitable replacement battery. Often the spec. listed is on the controller body.

 

[Pinesal]

I am toying with the idea of upgrading to lithium batteries but I have a question about that. My bike currently uses four 12v 20 ah sla batteries (48v). Am I supposed to replace it with four 12v 20ah lithium batteries? Or a single 48v 20ah battery?

If there is nothing tapping off a single 12V battery, then you only need to think in terms of total battery (48V XXAH). Its always good to get the schematic if you can.

Your controller specifications will be important in determining a suitable replacement battery. Often the spec. listed is on the controller body.

Does 4x 12v 20H = 48v 80ah?

Do I need to find a 48v 80ah lithium battery?

I can't find a 12v 20ah lithium.

 

[gogo]

Does 4x 12v 20H = 48v 80ah?

Do I need to find a 48v 80ah lithium battery?

I can't find a 12v 20ah lithium.

The voltage is additive, but not the capacity. 4(12V 20AH) = 48V 20AH

There are 12V 20AH batteries around, but the first thing you need to know is what draw your controller will place on them. SLA are capable of putting out many more amps than some lithiums, so finding the actual spec. of the controller is your next step.

 

[Punx0r]

If the batteries check out ok (voltage readings) and you crushed the motor cable you might want to check one of the wires inside isn't hanging on by only a few strands.

 

[Pinesal]

Thanks for the info, so I may be able to find a single 48v 20ah battery that will work?

I did find some 12v batteries but to buy 4 of them would be prohibitively expensive.

If I can get a single battery to do it, all will be well.

Sounds like I have more to learn on this subject as I don't completely understand what you mean about amp draw etc.

Edit: do I need to match, exceed or be below the rated amp draw of the controller?

 

[gogo]

Your controller will limit the maximum amp draw from your batteries. You need to know what that spec is when choosing a lithium battery that can handle it.

 

[Pinesal]

Ok so the battery should meet or exceed the controller?

 

[gogo]

Ok so the battery should meet or exceed the controller?

A main concern is the BMS on a lithium battery. It also has an amp limit, so you'd want the BMS amp limit to be higher than the controller's because some BMS's will shut the battery off when their limit is exceeded.

You might want plan for the future when the lithium is starting to wear out and has reduced capacity. In that case you'd need to start with a battery that can deliver 2X what the controller can demand so that it can still perform within spec when partially 'worn out'. Another strategy would be to retire the battery to a less stressful use when it starts to wear out, and replace it with the latest-greatest battery (which are improving every year).

 

[gogo]

If the batteries check out ok (voltage readings) and you crushed the motor cable you might want to check one of the wires inside isn't hanging on by only a few strands.

This could also cause the symptoms you described and might be accompanied by increased heat in the area of the 'few strands'.

 

[vptech]

If your battery charger is indicating full charge after charging and not right away, the batts are most likely good. If one of the four batts is fried, it would not likely charge enough for a green light. A lot of Chinese scoots have a speed governor jumper off the ECM. Usually a green wire loop. Often people find this wire disconnected and plug it in while doing work on the rear tire. Take a look for it.

Victor

 

[Pinesal]

Could this be my problem? The nut on the yellow wires was loose. Apparently, it was getting hot and was melting.

BTW ,The controller box has no info on it other than it's part number.

 

[gogo]

Yep, you found your problem.

 

[wesnewell]

Do away with that stupid block and put some 4mm bullets there and shrink tube them to keep water out and to keep them from coming apart.

 

[Pinesal]

Do away with that stupid block and put some 4mm bullets there and shrink tube them to keep water out and to keep them from coming apart.

Yeah, I did get rid of the box. The wires are connected to eachother directly and they've been sealed with tape.

The bike is running a little better now. I'd says it's somewhere between how it was before I fixed this and as good as it was when it was a few months ago. I'll take it for now.

Thanks for all the help. I will be visiting this forum often. Expect a lot more noob questions from me.

 

[amberwolf]

What do you mean by "directly"? Soldered together, crimped, twisted together, wire nuts, bolted together via the rings, new connectors crimped or soldered on and plugged together?

Any of those methods cna work, but some will have a lot higher resistance than others, and could explain the still-not-quite-right behavior.

 

[Pinesal]

What do you mean by "directly"? Soldered together, crimped, twisted together, wire nuts, bolted together via the rings, new connectors crimped or soldered on and plugged together?

Any of those methods cna work, but some will have a lot higher resistance than others, and could explain the still-not-quite-right behavior.

Bolted the rings together. I am very interested to hear about this higher resistance issue, thanks for bringing it up. I would do anything for faster acceleration and hill climbing.

 

[DAND214]

Did you replace the melted set? Once damaged, they are not the same.

Dan

 

[amberwolf]

Bolted the rings together. I am very interested to hear about this higher resistance issue, thanks for bringing it up. I would do anything for faster acceleration and hill climbing.

First question is: do the junctions get warmer than the wires? If so, the problem lies there. If not, it's somewhere else.


I re-used a bunch of Anderson SB50 sets off of server-sized UPSs and powerchairs, most of which used rings like that to bolt to the big SLA batteries. To make the sets I needed, without getting new contacts or wire, etc, I decided to bolt the rings together, and while they did work, some of them got warm under the electrical tape. Sometimes it was because my bolts weren't tight enough, and sometimes it was because either hte rings were slightly distorted and not sitting completely flat against each other, or because there was oxidation on their surfaces and that increased resistance.

I went for the quickfix at the time and just soldered them together while still tightly bolted together, using a little butane torch to heat it up just enough to melt the solder and flux, and this helped noticeably on most of the problem joints.

Some of them also required soldering the (apparently poor) crimps of the rings to the wires themselves. Didn't find that out till later.

But what really eventually helped was actually removing the rings entirely and directly crimping/soldering the wires together. There's a bunch of ways to butt-splice wires together; for thick ones I usually spread the strands apart just enough so I can stick the two together end to end as if you were sticking two brooms into each other, straw ends together, so the straw interleaves. Then I'd take some thin bare copper wire and wrap/twist it around the interleaved strands, trying to get them as tightly packed together as I could, then solder it (with the torch as the heat source, then, but now I'd use my big fat 90W Weller chisel-tip iron). If I had copper tubing the right diameter, I'd just cut a longitudinal notch down that and put it over the strands, then use a crimper to crimp the whole mess tightly together--but I didn't have that at the time.


Good bullet connectors, or Andersons, or any other type meant to carry high currents and be exposed to the elements would also work to join the two.

But I don't much like ring connectors for the purpose.