Questions about E-Bike battery upgrade

[wrathme]

Hi all, I got some questions about E-Bikes and I hope I get some answers here. My E-Bike is 250 Watts with Lead Acid 48V20AH battery (probably it has 4 x 12V20AH batteries inside I never opened it to be sure) and I need to replace the battery since it starts having problems. My questions about the battery change are:

1. Can I put a battery with more Volts if my controller supports max 60 volts or should I stick with 48V like the one I already have.

2. The controller has anything to do with the AH a battery has or it has limits on Volts only. Can I upgrade with a battery that has more AH like 48V80AH or my controller will not be able to handle it and will burn.

3. My controller can handle only Lead Acid batteries or it can handle other kinds of batteries like Lithium. Can I replace my old Acid Lead battery with a Lithium battery kit or I have to change some other parts from my E-Bike.

 

[dogman dan]

First thing, stick to "48v" 48v charges to 54v, possibly as high as 58v for lithium. so yer close enough to your controller limits right now.

AH means nothing much to your controller. it's kind of like the size of a gas tank. a 15 gallon tank car goes less far than a 20 gallon tank. But the car performs the same. So you won't hurt your controller with more ah.

Your controller does not care what the source of the electrons are. So you can replace your lead with lithium, and we recommend that. Get a 48v 10 ah, or larger. It will last longer than lead, and can stand deep discharges better, which results in nearly twice the distance from 10 ah lithium, than 10 ah lead.

 

[wrathme]

If I change Lead Acid with Lithium will I have charging problems? My E-Bike has a plug in that I can use to charge the batteries without taking them out, will this plug in work to charge Lithium batteries or Lithium use different charger and charge method?

 

[MikeSSS]

Lithium batteries are made up out of groups of cells. Several cells are wired in parallel, adding up to the desired Ah. Several of these groups are then connected in series to add up to the desired voltage.

Most lithium batteries include a battery management system, BMS, to ensure that each of the groups is fully charged, and that no group is overcharged, during the charging cycle. Li ion chargers and batteries typically have two plugs, the main charging plug and the balancing plug.

The chargers main plug, the one with the two thick wires, does most of the charging. The BMS has a connector, with several smaller diameter wires, it is also plugged in to the charger during charging. This many wire balancing plug is used by the charger and BMS to monitor the voltage in each of the groups of cells, that are in parallel, and to charge them to full charge as needed.

Lead gel cell batteries usually do not have a BMS board and do not have a balance plug. Your bike probably has the main charging port but not the BMS port. Once in a while I individually charge my gel cell batteries to ensure they are balanced. But, there is another way to ensure the gel cells are balanced, if the charger charges them to full charge and then changes to trickle charge mode, all the gel cells will eventually be balanced at full charge state.

If you change battery type from lead gel cells to, Li ion or Lipo, lithium batteries, it is a good idea to have a balance port for charging, to have lithium batteries that have a BMS board and balance plug, and to have a compatible charger that has a balance port, cable and plug.

If you buy a ready made lithium battery, it should include a built in BMS board and probably an appropriate charger, this is a common package deal. Your bike probably does not have a balance port, you might have to cut one in the battery box or remove the lithium battery for charging. You could also make extensions of the charging wires and balancing wires to exit the bike and be able to reach the lithium charger. This might be the simplest way. I like charging in the open, charging someplace where a battery fire won't be a problem.

Gel cell batteries, and Lipo batteries too, are damaged if you discharge them fully, I'm not sure about Li ion batteries. It is never a good idea to discharge any battery of these types all the way. That said, a Li ion battery can probably be discharged safely to a lower percent remaining charge than a gel cell battery. For this reason you might be able to get the same range from a Li ion battery that has a lower Ah rating than your lead gel cells. The Li ion battery should be lighter weight, compared to gel cells, as well, it should be able to produce more amps and therefore more power as well. Gel cells are subject to damage if you pull too many amps from them, their amp limit is less than that of lithium cells.

Here is a link to building lithium batteries from scrap or new old stock lithium cells. It shows building groups of cells in parallel and sizing all the groups by Ah, Ah determined by discharge testing. It also shows wiring the groups in series to give the desired voltage and then attaching the BMS wires. In this video, he has already completed one 24 volt battery and is building the second. When finished, both batteries will be connected in series to give 48 volts total. These batteries have a lot of Ah capacity, but they are big and heavy.

Because the cells he is using have various Ah capacities, he tests them, by charging them and then discharging down to 3.6 volts, using his Imax B6 charger, to find out their Ah values and then groups them according to Ah values. Some of his groups have 12 cells, some 13 and groups built from the lowest Ah cells have 14 cells to add up to the desired Ah capacity.

https://www.youtube.com/watch?v=Rjr2LKmhdVw

I'm not suggesting to copy his build, but his video does show how a battery can be built using a low tech, low dollar approach. He can solder the batteries with minimal heat because he is using a large, heavy soldering iron that has sufficient temperature and does not cool much when touched to the cells. He is also using solder that works well for this method. Result is that he can solder to the cells very quickly, transferring minimal heat to the cells.

Hope this helps. By the way, I'm a new guy, so take the above with a grain of salt.

 

[wrathme]

Will I have any problem if I use lower voltage batteries rather than 48V20AH like 32V20AH or my controller designed to work with 48V batteries only?

 

[MikeSSS]

Hmmm, good question and I do not know the answer.

If the 48 volt controller has a low voltage cutoff, of perhaps 40 volts, then it probably won't work with a 32 volt battery. The 32V battery has voltage below the minimum the controller will accept.

On the other hand, people have posted that a 36V controller will work with 48V, but the 36V controllers LVC, low voltage cutoff, will be too low for a 48V battery, and so you have to use a voltage meter and monitor the voltage when riding, to make sure you do not let the battery voltage drop so low, below 40V in this case, that battery damage happens.

 

[markz]

LVC (of the controller) is the limiting factor.

 

[d8veh]

You need a 48v battery. the most important thing is the dischare rate. You have to look at your controller to see what's the maximum current, then you need a battery that can provide at least that much continuously. My guess is that you should be looking for a battery with a maximum continuous current of 25 amps. The number of Ah doesn't really matter, although the more Ah, the further you'll go.

 

[USAEBIKECO]

Stick with 48 volt. Lithium would work fine with your controller.

 

[dogman dan]

Stick with 48v. Your new lithium battery will come with a charger that matches it. It should be possible to re wire your battery, and charger to use the same plug as before.

Charge lithium batteries in a safe place, where a fire, if it should happen, will not be a huge problem. So that usually means removing the battery from the bike after each ride anyway.

 

[wesnewell]

Will I have any problem if I use lower voltage batteries rather than 48V20AH like 32V20AH or my controller designed to work with 48V batteries only?

The LVC on your controller is ~42V for a 48V lead system. So the controller won't work with less than 42V. Now is the tricky part. Different types of lithium batteries have different voltage at which point they are considered empty. For rc lipo, that's ~3.3V per cell. For 18650 types it varies between 2.5-2.8V per cell, and for lifepo4, about 2.5V per cell. I would always want any of these set to ~0.2V higher than that to be safe. From this you can determine how many cells in series you want to use for your battery pack. 12s for rc lipo is perfect for a 42V LVC. For lifepo4, 15-16s would work fine. For 18650's, I wouldn't go over 14s.

 

[wrathme]

Lithium batteries are very good but they are very expensive to buy one from what i am seeing on sites. So in order to buy or create my own 48V20AH Lithium battery can someone recommend me:

1. Links to buy the materials i need to create my own 48V20AH Lithium battery
2. Links for ready 48V20AH Lithium batteries at low price

 

[MikeSSS]

Here's a link to the best information I've been able to find.

http://www.ebikeschool.com/how-to-build-a-diy-electric-bicycle-lithium-battery-from-18650-cells/

To build 20 Ah, take 20 Ah and divide by the Ah of the cells you will be using. Let's suppose you have chosen 2.6 Ah/cell cells.

20 Ah / 2.6 Ah/cell = 7.69 cells. So you would need 8 cells, wired in parallel, to build each group. A group of 8 parallel cells would have 20.8 Ah and the nominal voltage of those cells. Let's say the cells have a nominal voltage of 3.7 V, the single parallel group would have 3.7 V and 20.8 Ah.

To get 48 V, from 3.7 V cell groups: 48 V / 3.7 V/cell group = 12.97 cell groups. So, you would use 13 cell groups, wired in series. Each cell group would have 8 cells wired in parallel. This kind of battery would be called a 13S, 8P battery, meaning 13 in series and 8 in parallel. It can be thought of as 13 cells long and 8 cells wide.

Total number of cells needed is 8 x 13 = 104 cells. A battery management system, BMS, is also needed for this battery. Cost for the cells, good ones, and the BMS is "a lot".

Then there is building the battery: The cells are needed, a spot welder is needed as well as nickel strips and of course the BMS.

The ebike school site shows the whole build but for a battery of lower capacity.

 

[cycleops612]

Will I have any problem if I use lower voltage batteries rather than 48V20AH like 32V20AH or my controller designed to work with 48V batteries only?

The LVC on your controller is ~42V for a 48V lead system. So the controller won't work with less than 42V. Now is the tricky part. Different types of lithium batteries have different voltage at which point they are considered empty. For rc lipo, that's ~3.3V per cell. For 18650 types it varies between 2.5-2.8V per cell, and for lifepo4, about 2.5V per cell. I would always want any of these set to ~0.2V higher than that to be safe. From this you can determine how many cells in series you want to use for your battery pack. 12s for rc lipo is perfect for a 42V LVC. For lifepo4, 15-16s would work fine. For 18650's, I wouldn't go over 14s.

Thanks wes

some question if i may, to you and others?

so if i upgrade from an 18650 limn pak to a lifepo4 pouch pak, are there any traps with cutoff voltages etc. in the controller on my factory ebike (bofeili 250/350 w td1202z from longyeah. programming controllers is ambitious new ground for me.)?
https://www.alibaba.com/product-detail/27-5-Middle-motor-mountain-e_60230205689.html?spm=a2700.7724838.0.0.82Gocj

It must be a common scenario? Folks DO change chemistries/configurations as well as batteries on ebikes.

I understand the battery has its own programmed limits via the bms.

ought not protecting the battery be in the BMSs job, not the controllers? The battery assembler is best equipped to decide battery limits?

Similarly, the battery assembler usually provides a matched charger with protective limits also, so in the absence of regen, the controllers only concern should be its own limits of volts & amps that it can reasonably handle from whatever the battery can provide?

 

[wesnewell]

Lots of nice pictures in that bike link, but absolutely no useful info when it comes to the electrical system specs other than nominal 36V. IMO, most battery packs with bms's have the LVC set way too low. I've heard of lifepo4 cells set for as low as 2.1V per cell, which imo is way too low, even though it may coincide with the manufacturer specs. But they spec it at a 0.2C amp draw and take it to the absolute minimum voltage to squeeze every little bit put of it so they can show higher capacities per cell. At 2.7V almost ever bit of useful power is drained from lifepo4. Just like rc lipo is at the same point at ~3.3V per cell even though they state it's 3.0V per cell. The main concern for any battery pack is that it's rated to provide a minimum max amp output as the max amp draw of the controller you use.

 

[wrathme]

Nice I got a lot of things cleared from all these replies!

 

[cycleops612]

Lots of nice pictures in that bike link, but absolutely no useful info when it comes to the electrical system specs other than nominal 36V.

Sorry for the wild goose chase. Not smart in retrospect. I get hassled for no pictures a lot & for once had a link to a pic right handy. My intended point is its a nice bike w/ assumed better than average electrics like controller, but well hidden specifics, as they all do.

IMO, most battery packs with bms's have the LVC set way too low. I've heard of lifepo4 cells set for as low as 2.1V per cell

yes, i have seen similar since u mentioned it

, which imo is way too low, even though it may coincide with the manufacturer specs. But they spec it at a 0.2C amp draw and take it to the absolute minimum voltage to squeeze every little bit put of it so they can show higher capacities per cell. At 2.7V almost ever bit of useful power is drained from lifepo4. Just like rc lipo is at the same point at ~3.3V per cell even though they state it's 3.0V per cell.

very naughty of them to tell such deceptive and risky fibs about lipo.

The main concern for any battery pack is that it's rated to provide a minimum max amp output as the max amp draw of the controller you use.

Yes, which is why i get cranky about stock limn batteries sold to noobs. They almost never do. they sell 1c 350wh battery on a 350w battery, and within minutes, its much weaker than 350w.

Pls excuse my tardy thanks for your kind reply. You spun me out a bit. Just when i thought i had this stuff down, u throw me a huge curve ball i hadnt thought of - controller LVC.

Ie, what if, in the process of swapping chemistries (as am in the process of expensively doing), the lvc in the controller chops off the battery when its still half full~, or damages it by overdraining it as u point out?

Fortunately, the intended lfp battery has a lvc of 2.75v per lfp cell, which i can live with. I have never flattened a battery, and i hear they dont mind much if u dont leave them in that state - charge asap.I just have to hope the controller lvc isnt much higher than the batteryS lvc (reducing usable capacity), and that the controller doesnt have a cutoff maximum voltage ~below 44v.

As it happens, SEPARATELY, on another ebike upgrade to lifepo4, it is also very relevant info from you.

My plan is to take a bike with a 200w my1016z2 BRUSH motor, from a 200w 24v yi yun controller, to a 350w 36v YI YUN YK31c controller (i theory a simple plug compatible swap) & 36v lifepo4 pouch cell battery.

The motor comes in 3 forms, each in turn having diferent 3 power range configurations. The same my1016 motor as mine is rated to 200/250/300w in 24v form on the Unite Motor wholesaler sites~, so 350w at 36v doesnt seem excessive if 300w at 24v is ok - 10 amps on the new controller. What do you think?

Its geared down about 9:1 btw (its the reduction model), so keeping rpm up should be easy. Maybe u could cook it if u rode it hard on a hot day, but sensible riding paying attention to motor heat should be a reasonable risk? - or should i modify the shunt to reduce current a bit.

Getting info is worse than root canal work, but the lvc for the controller is 31v~ it seems (hence the product code?), and the battery BMS lvc is 33v - or 2.75v per lfp cell. So the battery bms will protect against over discharge, not the controller.

A dealer told me he regularly runs this combo at 48v on a 36v yk31c controller, but no more, so the max fully charged lfp battery voltage should be ok (~43.2v i think, 3.6vx12, but only a brief state, most always sub 40v).

More generally though, it does seem a sleeper problem. lvc requirements are very different i imagine for lipo/lmn/lifepo4/lead acid.

They sure make it hard to proceed with confidence in what must be a common scenario. Surely controllers ought give folks more accessible control and documentation over LVC (variable resistors e.g.?), or should one only consider programmable controllers given a choice?

 

[wrathme]

A question about battery chargers, can i use the charger my E-Bike had for it's 48V20AH Lead Acid battery to charge another Lead Acid battery with diferent V and AH lets say 32V10AH?

 

[Jon NCal]

A question about battery chargers, can i use the charger my E-Bike had for it's 48V20AH Lead Acid battery to charge another Lead Acid battery with diferent V and AH lets say 32V10AH?

No, that would wreck it very quickly by overcharge.

 

[wrathme]

What if i charge a same battery with same volts but different AH? Like 48V10AH. Will i have problem then to use same charger? Or my charger is only for 48V20AH batteries?

 

[Jon NCal]

What if i charge a same battery with same volts but different AH? Like 48V10AH. Will i have problem then to use same charger? Or my charger is only for 48V20AH batteries?

Same type and same voltage is okay. AH is not important in this case of lead acid battery.

 

[danielrlee]

Your old 48v lead acid charger will most likely be incompatible with a 48v lithium battery.

 

[wesnewell]

Batteries are stupid. They don't care where the voltage comes from or how much current the charger produces. I've charged many a rc lipo pack with an sla charger. Just don't overcharge it. Most 48V sla chargers will charge to about 60V, so be sure and remove it before you overcharge your pack. Most of the smart chargers won't start charging if they see a voltage too high also, but that's easy to fix with a simple precharge resistor to start the charge and then hook up the main leads. Now if your pack has a bms, you'll need to meet it's specs.