Building modular A123 pack: Questions: Wiring and charging

[inkeeper77]

WHAT:
So: I have determined A123 26650 cells are the safest and best option for me. I have decided to build them into packs of 6, so I can run two packs in series for 39v, or three for about 60v.
The series packs will then be hooked up in parallel for range.

I have a BASIC BASIC BASIC schematic (MSpaint) of what I want. Each block is a 19v 2.3Ah battery pack, 6 cell. They will be able to be disconnected, and have balance leads,etc

I can draw up another better schematic (maybe in a read CAD software) once I know what I need to be doing for battery protection..

WIRING QUESTINS:
Now, how would I wire this for safety? I have been reading and I have found two problems with my original idea of simply connecting them with strong wire and charging them as separate batteries- I have no protection for batteries charging other batteries in bad ways.
Can I use diodes and fuses in the batteries to protect them and allow them to run as I had envisioned? I do not know the proper way of doing that. (I also happen to have 10x 10ga fuse holders!)

Also, charging. Apparently A123 can be charged VERY quickly and do not need balancing every charge- I would love this, as I could then extend my range by recharging halfway. I would prefer to always balance charge at home though. How would I go about wiring the bike to quick charge everything, safely? Would this even be possible? (39V, with 4+ parallel banks of 12x 26650's) - a 20-30 minute charge would be so absolutely fantastic for what I want.. Do I just electrically cut the positive lead to the bike motor controller, and plug in a charger?
There is a possibility I will want this to go for 60 miles one way a few times. Additional battery packs are a possibility, but charging on the way would be sweeeet.

Switches: So I hear rush current is bad and breaks things. How do I prevent this? Protecting the bike electricals is the main priority, second is the batteries, third is the power switch between the two.

Would I just disconnect the batteries from the bike at the main

Battery safety: I do NOT need balancing! I will be balance charging them 8 times out of 10 (hopefully)

CHARGERS QUESTIONS:
Also, I have been looking but cannot find much info: What charger is the best compromise between price and quality? Safety is a BIG issue, I wouldn't mind a slow balance charger, even if I did have to charge each pack separately. However, a inexpensive fast bulk charger if I could do that would be nice. I dont even know what type of balance leads I will need yet.

PS: Is there a standard way to keep balance charging safer for indoor usage? Would a sand bucket help?

Budget: $200 over the cost of cells. Is this reasonable?

Thank you everyone! Sorry about all the questions. I hope they are at least also useful to others!

 

[dogman dan]

Paralell then series is the norm.

 

[inkeeper77]

But do I not need some ideal diode setup? These packs will be separated regularly- not ideal for safety.
I will NOT be using regen- it is impossible on my setup anyway.

Apparently a series diode will also work, with less efficiency. I still dont know to make, buy, or wire either type.

I am not quite sure of how I should go about this- apparently 2 mofsets can be used to rig up an ideal diode. How easily is this done?
I will also see if my roomate can produce some ideal diodes that work like these: http://www.re-voltage.eu/electronicsID80V2.html

Also, is there a circuit I can make in order to slow down the current when connecting, in order to protect the system?

 

[CyclemotorEngineer]

If you are going to add and remove series strings of cells from a parallel array, you ought to place a diode in series with each string, since they may vary in capacity and voltage. Schottky is the best choice for this because it minimizes your power loss. Here is a part that works well up to 30A if properly heat sunk:
V30100S-E3/45 DIODE SCHOTTKY 30A 100V TO-220AB Digi-Key Part Number V30100S-E3/4WGI-ND

 

[ninjamik]

just to throw something out there?..

does anyone know if its possible to make a paralleled up set of a123s say a 36v pack be connected in series to a 36v pack of headways??

I'm hoping it is possible, i presume the whole 72v pack would stabilize the cells to the less powerful ones (the headways?) is this anywhere near correct..

anyone have experience of this??..

dont ask me why the mix!...its to do with shape,, combination of form factors of the same chemistry to make a smaller battery...

i realise, if if it is possible that you presumably would lose some of the a123s power, like if the headways are 16ah n the a123 20ah maybe?

but worth it if clever about construction to not get a power cube!!

 

[inkeeper77]

If you are going to add and remove series strings of cells from a parallel array, you ought to place a diode in series with each string, since they may vary in capacity and voltage. Schottky is the best choice for this because it minimizes your power loss. Here is a part that works well up to 30A if properly heat sunk:
V30100S-E3/45 DIODE SCHOTTKY 30A 100V TO-220AB Digi-Key Part Number V30100S-E3/4WGI-ND

As far as wiring up those Schotty diodes, would I just put them in series on the positive lead on the battery pack (x 6 cell in series) prior to connecting it to the positive lead of the motor controller (where all of the other battery packs would also connect)? Also, what is the third pin on those diodes for?

Thank you!

 

[CyclemotorEngineer]

Yes to your first question. This Schottky package contains two diodes, and the center pin is common to both. Download the spec sheet for polarity and other ratings.

 

[inkeeper77]

Thank you! Will do! This is nice, I have a much better idea now of what to do.

Lastly, chargers- for a balance charger, would an Accucel-8 be good enough, or do I want to spend the extra on an icharger-106b or something? Also, I still am unable to find a good listing of 12v power supplies.. and also, bulk chargers?

 

[dnmun]

not sure if you should attempt this if this is all you know so far about battery packs. maybe start with something like a ping that is already built with the BMS to protect it, and then buy a voltmeter and learn how to care for the ping pack and after a while you will know whether you wanna build your own pack. there should not be diodes inside the pack, you should not build it with the 2 cells in series with the others in parallel like that diagram, all this is gonna be a waste. you have to have a BMS and it has to be something like 12S or 16S to use the chargers available.

the headway pack build thread has buncha different builds in it too.

 

[ElectroSurf3r]

I agree that each row should be in parallel. This is just a matter of a balance wire for each row though... trivial.

The real issue: Some promote BMS. I DO NOT. Here's why:

We run on a DIY homemade A123 pack, as you propose. 23s8p setup. The A123 M1 cells were harvested from used dewalt toolpacks, matched up for similar capacity in series strings, then connected in a parallel with a balance wire on each row. We terminated the balance wires at large plugs that make it easy to check voltages between rows. The cell row voltages are monitored daily...ish The bike gets multiple trips a day, and the pack sees around 100A peak, so 6.25 C discharge peaks. It has performed without a hitch.

I don't use a BMS, and never have on any of my packs. NONE have failed yet, but get old and saggy after running for years without problem.
Those were mostly konions though, and don't have the same C Rating and ability of A123 chemistry. Both of these cells are safe... in my opinion the sandbox is not necessary until you have RC LiPo.

I have opened up MANY toolpacks with Chinese-made BMS boards, and find that the first cell row is dead. A budget level BMS is just going to cause problems, and may only be offered on lower C-rated cells (lower amps). Plus these packs will be more expensive.
We bulk charge after each ride for much quicker charge time. All the maintenance tools you need are ONE iCharger, some cheap 12V lead acids, and a multimeter to keep your balance in check. Each row monitored daily with a multimeter, and corrected by the balance charger if necessary...which for us has been an average of maybe once a week because one row is 0.1V different. It's that easy.

This is a DIY forum, so there's plenty of knowledge to go for it on your own! Plus if you construct your own, you will have the tools and knowledge to maintain and repair your pack if necessary... instead of the BMS killing your pack and then you're boned.

Oh and another note... I'm not sure you need any diodes to be able to separate your pack. Here's how I would do it:
Put good connectors between packs that will be in series and will be separated often. Keep a pre-charge resistor on you for reconnnecting. Disconnecting battery from the controller is safe IF POS AND NEG ARE ISOLATED... don't let the positive touch the negative on either the battery or controller, or else fireworks.
This can easily be achieved by planning the connectors before soldering, and being careful when disconnecting leads (especially battery leads if you will be carrying them).
When reconnecting, first connect the series packs to make one battery pack, then connect the positive lead to the controller. Bridge the pre-charge resistor between the negative leads for a couple seconds (this charges the caps and prevents arcing and the controller from getting a sudden jolt). Then connect the leads and ride away.

If you'd like some more tips, steps, etc on DIY A123 packs, I'm happy to help.

 

[inkeeper77]

not sure if you should attempt this if this is all you know so far about battery packs. maybe start with something like a ping that is already built with the BMS to protect it, and then buy a voltmeter and learn how to care for the ping pack and after a while you will know whether you wanna build your own pack. there should not be diodes inside the pack, you should not build it with the 2 cells in series with the others in parallel like that diagram, all this is gonna be a waste. you have to have a BMS and it has to be something like 12S or 16S to use the chargers available.

the headway pack build thread has buncha different builds in it too.

No time like now to learn though! I will also be running everything past my roomate, who is a junior electrical engineer. (I am a mechanical, thus all my questions.. but I am pretty sure I will be able to handle it)
Why would 2 (packs) in series be a waste? The series are to get the volts up to about 40V while still having the packs small and easy to maintain- think of each series pack as one large 12S pack. Parallel is to get the aH up to a usable level- with one series set, I would have a mere 2.3 aH- almost useless. In parallel with 4 sets I would have 9.2 aH avalible. I really dont see where the "waste" comes into play.

I agree that each row should be in parallel. This is just a matter of a balance wire for each row though... trivial.

We run on a DIY homemade A123 pack, as you propose. 23s8p setup. The A123 M1 cells were harvested from used dewalt toolpacks, matched up for similar capacity in series strings, then connected in a parallel with a balance wire on each row. We terminated the balance wires at large plugs that make it easy to check voltages between rows. The cell row voltages are monitored daily...ish The bike gets multiple trips a day, and the pack sees around 100A peak, so 6.25 C discharge peaks. It has performed without a hitch.

We bulk charge after each ride for much quicker charge time. All the maintenance tools you need are ONE iCharger, some cheap 12V lead acids, and a multimeter to keep your balance in check. Each row monitored daily with a multimeter, and corrected by the balance charger if necessary...which for us has been an average of maybe once a week because one row is 0.1V different. It's that easy.

Oh and another note... I'm not sure you need any diodes to be able to separate your pack. Here's how I would do it:
Put good connectors between packs that will be in series and will be separated often. Keep a pre-charge resistor on you for reconnnecting. Disconnecting battery from the controller is safe IF POS AND NEG ARE ISOLATED... don't let the positive touch the negative on either the battery or controller, or else fireworks.
This can easily be achieved by planning the connectors before soldering, and being careful when disconnecting leads (especially battery leads if you will be carrying them).
When reconnecting, first connect the series packs to make one battery pack, then connect the positive lead to the controller. Bridge the pre-charge resistor between the negative leads for a couple seconds (this charges the caps and prevents arcing and the controller from getting a sudden jolt). Then connect the leads and ride away.

If you'd like some more tips, steps, etc on DIY A123 packs, I'm happy to help.

I like the idea of individual row balance wires!

Question though- what bulk chargers do you use? I havent been able to find much info on that.. and I would rather someone point me in the right direction at least for my first build! Thanks

Pos & Neg isolation- that will be easy with the physical setup I am working on, and the connectors will all make shorting them VERY VERY difficult.

What size resistor would you recommend for a pre charge resistor?

I am still considering diodes, if only to prevent any human stupidity on that part and also to experiment with. They are cheap enough.

 

[ElectroSurf3r]

Balance wires on each cell level are a MUST for A123s.
The only available self-balancing cells are Konions (LiMn 18650s). They don't need balance wires if the pack is built well and treated properly. A123s must be monitored for balance though.

I believe our pre charge resistor is 300 Ohms for our packs at 82v. Others have recommended 200-300 ohms. Make sure the resistor is beefy to handle decent current.

For bulk charging, we use two 36V DeWalt toolpack chargers, outputs wired in series to give us around 82V hot off the charger (72V nominal). They do the trick, but aren't high current (3A I believe), and so take a little longer to charge. If you need rapid charging, you need to look into Meanwells, etc. Keep charging current well under the max amps allowed by your pack, which is determined by multiplying the "C Rating" of your cells by the nominal capacity of each cell (in Ah), and multiplied again by the number of cells in parallel.
For example, a pack with cells rated for 10C, and 2 Ah apiece, arranged in a 5p pack, is capable of 10 x 2 x 5 = 100A maximum current.
The maximum battery-side current of the controller should also be set within this limit for discharge and regen!

What is the nominal voltage you are looking to run? If you want 36, 48, 60, 72 etc, its pretty easy to make a decent bulk charge solution with used toolpack charger(s), or laptop chargers... A fancy charger with higher amps (like the Meanwells) will be way more pricey.

 

[999zip999]

Paralell then Series is the best if you go a different way you will get less ah and have to lower your amp draw. And the pack is harder on each cell in those sub packs. You will be caring extra weight that you can't use, so to speak. Like it or not.

 

[inkeeper77]

Paralell then Series is the best if you go a different way you will get less ah and have to lower your amp draw. And the pack is harder on each cell in those sub packs. You will be caring extra weight that you can't use, so to speak. Like it or not.

Can you show me the math behind that? I can diode protect the packs in my current configuration.


Also, I drew up a simple schematic between classes today. It has a simple switching precharge circuit.

another possibility for precharging the motor controller would be to put a LARGE inductor in series with the positive battery terminal, post switch. This would enable the battery current to ramp up into the controller, protecting the switches and batteries. (after a few seconds it would effectively be an open circuit) A large power resistor could be put in parallel with that inductor in order to prevent arcing on disconnection. Is there anything seriously wrong with this setup? Will the motor controller need a ton of current all at once through the batteries that a simple inductor would prevent from being delivered?
This is very very quickly drawn out in the lower right of the schematic.

Image!

One think i am not sure of is the lighting system wiring...

 

[CyclemotorEngineer]

999,

Modular parallel packs using the A123 chemistry is fine, so long as current draw for a single string is within their ample capabilities. I have two strings of 20 cells each, and on really short trips might draw 1200 W through one string w/o mishap. Been using since 2007 w/ over 1000 cycles on both strings.

 

[999zip999]

O.k. I say it can be used with a123's if you keep the amp. draw lower than if in a parelle than series app.. Just because they are a great cell. You still will have a different acting battery. For ease up use and charging.

 

[ElectroSurf3r]

Any added inductance or resistance that is between the battery and controller is bad!
Even thin or long wires between the 2 has been known to cause problems. It's adding inductance and resistance between controller and MOTOR that can be helpful (by easing the spikes in what the controller gets back from the motor).

An inductor in series will NOT act like an open circuit here, because our batteries and controllers both spit out waves that cycle many times a second. The batteries DON'T just spit out constant DC voltage, constant current while riding!

Trust me, once the controller is on, you don't want ANY resistors or inductors between the battery and controller. You also want low resistance wiring (short as possible and fat) between the two. A switching circuit for the pre-charge would be cool though. i.e. an open switch forces the current through the resistor for plugging in, then close the switch to bypass the resistor for riding. The problem there is that the switch needs to be able to handle high current, which will be VERY hard to find for a decent price.

 

[inkeeper77]

That makes sense! I did not realize that batteries output waves.. I shall stick with the switching pre-charge circuit then! (And 10 to 12 Ga wire) I may add an inductor on the pre charge as well to help the switch even more.

The switch I am thinking of for the main switch is using heavy duty connectors to be a jumper. (Like this RC version http://www.rcgroups.com/forums/showthread.php?t=983802&highlight=tomapowa )

 

[ElectroSurf3r]

The battery sends whatever the controller wants, which is rapidly changing. The controller does not want to see a lag (inductor), or a decrease (resistor) in the available power that it needs asap.

A precharge resistor allows a slow current to flow into the controller and fill the capacitors without arcing. Once the controller is filled, quickly plug the last battery lead.

 

[inkeeper77]

So I think that is pretty much all settled. Simple pre charging circuit only, no inductance. I still am unsure of how I would want to bulk charge though- do I just find a charger that cuts off at3.6v per cell? (Recommended standard charge: 3A to 3.6v / cell CCCV, recommended fast charge: 10A to 3.6v /cell CCCV)
It also says recommended pulse charge / discharge cutoffs are 3.8 V / 1.6 V

Can I just have BMS battery make me a charger set to 43.2 V?
http://www.bmsbattery.com/alloy-shell/26-alloy-shell-400w-lifepo4li-ionlead-acid-battery-ebike-charger.html

If I were to get a charger of slightly lower voltage per cell, would it still work as an on the road bulk charger, to charge to that capacity? For example, the for sale used section has a few chargers.
Here is a 42V charger: http://endless-sphere.com/forums/viewtopic.php?f=9&t=35270
Here is a 42.2 and a 43.8

3.6 v per cell across 12 cells is 43.2 V, and 3.8 is 45.6 - could I just get the 42 V charger, or would I get the cheaper 43.8 V charger? Or something totally different?

Thanks!

 

[CyclemotorEngineer]

elecrtosurf,

With an adequate controller filter capacitor, there will be very little AC on this line and an inductor will serve to limit the inrush current when the battery charges this filter capacitor. The old Dewalt packs contained a BMS which would shut down due to this inrush, and inserting an inductor solves this problem. The inductor stays cold to the touch at high power levels, so QED. See this thread for details:
http://endless-sphere.com/forums/viewtopic.php?f=14&t=10986

 

[biohazardman]

Ok I have been running a123 cells like these for several years now. My first two packs 48V 14s 2p were wired for balancing and I built one of the TP Packs version 2.3 BMS units, great units by the way, but only use it for charging as the controller has a useful LVC built in as most do. The LVC kicked in probly 25% of the time on my rides usually very close to home. I balance charged always until I figured out that it was not needed as battery voltages stayed very close for months on end. On my second e-bike build I upped the voltage and went to 20s 2P soon to be 3P without balance leads. I check my packs now and then, used to be weekly then monthly but even less now as they seem to do just fine without it. Running @ 66V and a couple of 4.6 packs on a BMC V2 with 45A controller. I have been using this switch, see link, with no pre-charge for years without problems. if you are pulling 40+ amps continuesly you could just wire up two to make sure.

http://endless-sphere.com/forums/viewtopic.php?f=2&t=35187

What I am trying to say is that if you start with good cells and they are balanced to start with they will stay that way for a long time. So long as you can get to them to check for proper voltage and balance now and then, but seldom, you are in good shape. I have a single cell LifePo4 charger for balancing if it is needed.

Precharge resistors, diodes and most of the rest of the stuff brought up here are not usually needed. You would be better off with a DC-DC converter on the lighting as it draws evenly from the whole pack thus no balancing needed.
I believe in the Kiss system "Keep it simple stupid" for anything I do the less parts/wiring the less problems down the road.

Balance wires ratsnest first try

66V no balance wires

Extra pack for more range

 

[biohazardman]

I agree that each row should be in parallel. This is just a matter of a balance wire for each row though... trivial.

The real issue: Some promote BMS. I DO NOT. Here's why:

We run on a DIY homemade A123 pack, as you propose. 23s8p setup. The A123 M1 cells were harvested from used dewalt toolpacks, matched up for similar capacity in series strings, then connected in a parallel with a balance wire on each row. We terminated the balance wires at large plugs that make it easy to check voltages between rows. The cell row voltages are monitored daily...ish The bike gets multiple trips a day, and the pack sees around 100A peak, so 6.25 C discharge peaks. It has performed without a hitch.

I don't use a BMS, and never have on any of my packs. NONE have failed yet, but get old and saggy after running for years without problem.
Those were mostly konions though, and don't have the same C Rating and ability of A123 chemistry. Both of these cells are safe... in my opinion the sandbox is not necessary until you have RC LiPo.

I have opened up MANY toolpacks with Chinese-made BMS boards, and find that the first cell row is dead. A budget level BMS is just going to cause problems, and may only be offered on lower C-rated cells (lower amps). Plus these packs will be more expensive.
We bulk charge after each ride for much quicker charge time. All the maintenance tools you need are ONE iCharger, some cheap 12V lead acids, and a multimeter to keep your balance in check. Each row monitored daily with a multimeter, and corrected by the balance charger if necessary...which for us has been an average of maybe once a week because one row is 0.1V different. It's that easy.

This is a DIY forum, so there's plenty of knowledge to go for it on your own! Plus if you construct your own, you will have the tools and knowledge to maintain and repair your pack if necessary... instead of the BMS killing your pack and then you're boned.

Oh and another note... I'm not sure you need any diodes to be able to separate your pack. Here's how I would do it:
Put good connectors between packs that will be in series and will be separated often. Keep a pre-charge resistor on you for reconnnecting. Disconnecting battery from the controller is safe IF POS AND NEG ARE ISOLATED... don't let the positive touch the negative on either the battery or controller, or else fireworks.
This can easily be achieved by planning the connectors before soldering, and being careful when disconnecting leads (especially battery leads if you will be carrying them).
When reconnecting, first connect the series packs to make one battery pack, then connect the positive lead to the controller. Bridge the pre-charge resistor between the negative leads for a couple seconds (this charges the caps and prevents arcing and the controller from getting a sudden jolt). Then connect the leads and ride away.

If you'd like some more tips, steps, etc on DIY A123 packs, I'm happy to help.

I was wondering where all of the a123 cells went That is alot of cells you have there I'll send you my addy so you can remember to put me in yer will. ;^)

 

[tranquility]

But do I not need some ideal diode setup? These packs will be separated regularly- not ideal for safety.
I will NOT be using regen- it is impossible on my setup anyway.

Apparently a series diode will also work, with less efficiency. I still dont know to make, buy, or wire either type.

I am not quite sure of how I should go about this- apparently 2 mofsets can be used to rig up an ideal diode. How easily is this done?
I will also see if my roomate can produce some ideal diodes that work like these: http://www.re-voltage.eu/electronicsID80V2.html

Also, is there a circuit I can make in order to slow down the current when connecting, in order to protect the system?

Here is the basic circuit for an ideal diode. You would need to change this circuit for higher current/voltage.

http://www.discovercircuits.com/DJ-Circuits/ideal-diode.htm