What exactly do I need to leave a pack charging unattended?

Ok, so I recently purchased a 24s mini-bms system from clean power auto for use with 40ah thundersky cells, and I'm in the process of hunting down a charger, but this is my first time putting together a pack, and to be entirely honest I'm just not sure what all I need to have in place before I can plug this thing into the wall and forget about it for a while.

So far my plan is to either pick up 3 24v hiccup mode meanwell power supplies and one of the tppacks current controllers, or just track down some constant current limiting powers supplies. I'm guessing at that point there isn't much more to it than stringing the power supplies together in series and running it through the bms per what ever instructions come with the system, but I really want this set up to be idiot proof, so I'm wondering if there is anything more I could include in the circuit so that I can just set it and forget it without any need to worry that I might fry some batteries or something.

At any rate, any input that people have would be greatly appreciated.

I don't believe that will work. you'll want a charger that will stop charging at 3.9v per cell, which should be um.93v or so, which is the cutoff point for 24s. 3 24v supplies will only go to 75v, which isn't what you want.

Not sure what the solution is for that. I built an 88v charger out of 4 laptop PS's and12v portable hard drive charger, all in series. it worked, but wasn't a good long term solution. I just needed to get juice in the pack and get to work.

anyone?

Yeah, I'm still a little fuzzy on that, but it doesn't seem as though lifepo4 batteries are categorized according to their their maximum possible voltage. For instance I've always seen 48v thundersky packs with either 15 or 16 cells, as opposed to say, the 13 that you would assume are necessary to reach 48v if you charged each cell to 3.8v. I'm guessing that has something to do with the voltage being different under load, but I'm not really sure. Even so though, you would think that the charger would need to be rated at the maximum voltage of the battery, but every official thundersky charger I've seen likewise seems to be described as something like a "48v charger for 15 cell packs" or the like. I've ordered a 6a single cell charger for the time being, which should at least help me to manually balance the pack, but I definitely want to figure this stuff out by the time I actually have the pack attached to the bike.

yea, that's the difference between fully charged voltage, which should be 4.2v per cell, and the Nominal voltage, which is the voltage that each cell is at 50% discharge. cells are normally listed at their nominal(half full) voltage. Lifepo4 that's 3.2, LiPo that's 3.7, Nimh it's 1.2, Lead acid is 12v.

to fully charge each type, you'll need to go to 4.2v per cell for Lifepo4, so a 48v charger for lifepo4 will actually charge to 54v, IIRC.
a Lead charger will charge to 14.xx volts
a lipo charger will charge a 6s 22.2 volt nominal pack to 25.0 volts.


so, yea, the numbers used to describe the cell, and the numbers that you need to reach for the cell to be "full" are two different things.

What exactly do I need to leave a pack charging unattended?

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A good fire insurance policy and fire suppression system.

thundersky cells, aren't they LiFePo4? I don't think you want to charge them to 4.2v per cell. 3.85 might be the limit maybe 3.9 but not 4.2v. LiPo are higher voltage around 4.2v per cell but best for lifespan you don't want over 4.15 or lower.
Dan

Ok, so I take it that what I need is a set up that charges at 91v, but a controller that is optimized for use with a 72v nominal system. The controller I have is one of Lyen's "deluxe" 72v 18fet (I think its based on the infineon boards) controllers with regen, and it seems to be pretty easy to tweak voltage settings and what not, so I think I'm good on the controller side. In an ideal world I would just plop down the cash for a "72v" lifepo4 charger, which I'm guessing would in actuality be set up to charge at 91v, but the prices on these things border on obscenity (I simply don't have $500+ to drop on a 10a 72v charger when 20a 24v power supplies can be found for less than $50 a pop), so I suppose my best bet is to string together some meanwells. Ninety-one volts is a little akward though, I hadn't considered mixing different voltage power supplies to get the voltage I need, but it seems like that is what I am going to have to do unless I want to scale back my pack size. Not that scaling back my pack size would kill me or anything, right now my pack is sized so that I will only occasionally going below 50% charge, but its definitely on the heavy side, and the only thing really forcing me to go with 24 cells is the fact that I've already dropped the cash for 24 mini bms units. Speaking of Mini-bms, I'm also wondering whether if a straight bulk charge is completely safe, I'm kind of just assuming here that Mini-bms will take care of making sure that each cell gets independently topped off at exactly 3.8v and that as a result I don't need to worry about going through separate constant current and constant voltage phases the way the fancy lifepo4 smart chargers do, but I'm not really sure about that either.

just series 2 36v Lifepo4 chargers.

http://www.pingbattery.com/servlet/the-25/2.5A-Charger-for-36V(12s)/Detail

aaronski said:

just series 2 36v Lifepo4 chargers.

http://www.pingbattery.com/servlet/the-25/2.5A-Charger-for-36V(12s)/Detail

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With 40ah batteries it just doesn't seem to make sense to use the low amperage hobby chargers. I mean, yeah I probably could series two of these to get the voltage I want, but then I'd also need to run about 5 of them in parallel per 36v just to get 12.5a. Even if it didn't over complicate things, it would still wind up costing me a lot more in the end.

how quickly do you need to charge? I almost always charge overnight.

How big is your pack though? If its comparitively small, and it takes you overnight to charge, then we're not even in what I'd consider to be the same ballpark as an acceptable charge time. I mean, granted, I don't intend to completely discharge the pack on a regular basis, but I'd still like to have the option of stopping at a cafe or something to top off the pack and still stay under the 45-ish min range. I suppose part of it is just the fact that I'd like to take advantage of the fact that this chemistry allows me to do a reasonably quick charge without doing any damage. On the one hand I figure .5c should be a pretty conservative charge spped, and that I'm not really going to get any improvement in cycle life if I go lower than that, on the other hand it seems that once I hit 20a at 90v I'm looking at pulling the same wattage as a medium sized space heater, and if the frequency with which those things trip breakers and burn up wall sockets is any indication, the faster charge time won't be worth the trouble, so I figure somewhere near 15a is pretty optimal.

BMS stands for Battery Management System. It should be in charge of overseeing the charging process too. Find out what voltage it needs to see from the charger and supply it with a couple of Meanwell power supplies.

For unattended I prefer the charger to also be on a time. Once you get familiar with your pack, then you'll get a good feel for charging time requirements. With a timer then even in the worst case the pack can't go to serious overcharge.

I have a Thundersky 16S x 40 AHr pack. Current recommendation from those in the know around here is 3.6 volts per cell fully charged to maximise cycle life.

I use a Meanwell current limited power supply to bulk charge. The BMS then further limits the current to 1/2 amp for balancing, topping off the rest of the cells after the first cell is fully charged. Once all cells reach 3.6 volts, the BMS cuts the current completely.

The mains input to the Meanwell is switched by a relay, held in by a circuit which monitors the charge current. Charging is started by a momentary press button in parallel with the relay contacts. When the BMS switches off the final charge current, the relay drops out and everything stops.

But you can't buy this setup off the shelf, sorry.

commanda said:

I have a Thundersky 16S x 40 AHr pack. Current recommendation from those in the know around here is 3.6 volts per cell fully charged to maximise cycle life.

I use a Meanwell current limited power supply to bulk charge. The BMS then further limits the current to 1/2 amp for balancing, topping off the rest of the cells after the first cell is fully charged. Once all cells reach 3.6 volts, the BMS cuts the current completely.

The mains input to the Meanwell is switched by a relay, held in by a circuit which monitors the charge current. Charging is started by a momentary press button in parallel with the relay contacts. When the BMS switches off the final charge current, the relay drops out and everything stops.

But you can't buy this setup off the shelf, sorry.

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Yeah, I took a closer look at the instruction pdf for mini-bms over at cleanpowerauto and it seems to be suggesting a setup that sounds pretty close to what you're working with. The version of the BMS I ordered is set to shunt at 3.8v (I probably would have gone with the 3.65v version if I had known that it would be easier on the batteries, but 3.8 is what cleanpowerauto suggested for thundersky), and apparently I should be fine with meanwells as long as I run their power input through a solid state relay (which mini bms will automatically switch open when the the last cell starts shunting). At any rate, I ordered a 40a ac relay this morning (not that I'll likely ever pull anywhere near 40a at 120v, but I figured it couldn't hurt to be on the safe side), and I've started shopping around for power supplies. I'm guessing that my PS voltage should be slightly higher than my total max voltage, so I figure I'll just get 2 48v 15a meanwells, or maybe cut my pack size back to 20 cells and pick up 3 24v meanwells.

Had a quick look at the pdf you mentioned.

It needs an auxiliary 12 volt supply. They talk about using a 12 volt battery. This sounds like a motor car application.
My setup uses 12 volts to power the bms, but I pull it straight from the Meanwell, and run 3 wires from charger to scooter.

Don't know about the meanwell 48 volt 15 amp. Particularly what it's current limit setup is. You need a supply with Constant Current (CC) NOT hiccup mode.

The S-350-48 that most of us use, and which is well documented here in other threads, is CC, and can be modified so the current limit is lower than the factory pre-set 130%.

commanda said:

Had a quick look at the pdf you mentioned.

It needs an auxiliary 12 volt supply. They talk about using a 12 volt battery. This sounds like a motor car application.
My setup uses 12 volts to power the bms, but I pull it straight from the Meanwell, and run 3 wires from charger to scooter.

Don't know about the meanwell 48 volt 15 amp. Particularly what it's current limit setup is. You need a supply with Constant Current (CC) NOT hiccup mode.

The S-350-48 that most of us use, and which is well documented here in other threads, is CC, and can be modified so the current limit is lower than the factory pre-set 130%.

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Yeah, I'm not really sure why they do a separate 12v line for powering the bms. I figure I can always just run a little 12v power supply to it in a similar fashion to what you've done. Unless of course it requires that external 12v even when you aren't charging for what ever reason, in which case I suppose I'll just have to find a dc to dc converter. It says it only requires something like 50mw though, so I'm not all that worried one way or the other, if it comes right down to it I can just run it off its own little rechargeable battery in the bms box. At any rate, I'm not particularly certain that there even is a 15a model of the 48v meanwells floating around, I just meant that I would probably wind up using something along those lines. I figure I'll either pickup some of the CC meanwells (or some other brand with CC limiting), or pick up some of the hiccup mode supplies and use the little current limiting widget from tppacks. Either way, my main concern right now is just being sure that I am operating at the right voltage for my system. It looks like at 3.8X24 I'd have a max voltage of 91v, and I'm hoping that the 96v I get from 2 48v supplies in series will be close enough that there wouldn't be any problem with that (or in other words that I will be able to tune the meanwells to hit that voltage). I should probably also check with Lyen to make sure that my "72v controller" means 72v nominal, rather than 72v max, or maybe I will just see if I can't trade controllers with someone who wants a 72v controller with regen, for a more simple controller that is suited to higher voltages (to be honest, I'm not even sure how I would set the system up to work with regen, the pdf doesn't seem to make any mention of it).

The Meanwells do have a voltage adjustment pot. Adjustment range is in the pdf datasheet. And they can be hacked to take it a little higher or lower.

Regen on a light-weight vehicle is generally deemed "Not Worth the Effort".

commanda said:

The Meanwells do have a voltage adjustment pot. Adjustment range is in the pdf datasheet. And they can be hacked to take it a little higher or lower.

Regen on a light-weight vehicle is generally deemed "Not Worth the Effort".

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Yeah, it looks like I should be fine, I only need to pull the voltage down by 2 or 3 volts per power supply. I think I am going to try to sell that controller for that matter too, I've been looking over its specs and I think its just plain got more bells and whistles than I'd honestly know what to do with. Maybe I'll try to implement regen in some future project, but for my first bike its probably just going to wind up being more frustration than I want to get into.

Indubitably said:

Yeah, it looks like I should be fine, I only need to pull the voltage down by 2 or 3 volts per power supply. I think I am going to try to sell that controller for that matter too, I've been looking over its specs and I think its just plain got more bells and whistles than I'd honestly know what to do with. Maybe I'll try to implement regen in some future project, but for my first bike its probably just going to wind up being more frustration than I want to get into.

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I've pulled the voltage down on one of mine with diodes in series. wastes a lot of heat, but it works and it's easy. Only useful if you can't adjust the POTS though. the charge wire just has a series of 5 diodes at the end of the pos wire, wrapped in duct tape. I'm not sure if that's a heatsink or insulation, but it keeps ME from being burned, which is all I care about.

I'd say keep the controller for one reason, it's tough as hell. you don't have to use the bell's and whistles, but Lyen beefs em up proper, so when you abuse it going full throttle on a hill, the guts of this controller much less likely to melt. I've put 6000 watts through my 12 fet with no problems yet.
If you really don't want it though, Edward will take it back if you haven't used it.

aaronski said:

I've pulled the voltage down on one of mine with diodes in series. wastes a lot of heat, but it works and it's easy. Only useful if you can't adjust the POTS though. the charge wire just has a series of 5 diodes at the end of the pos wire, wrapped in duct tape. I'm not sure if that's a heatsink or insulation, but it keeps ME from being burned, which is all I care about.

I'd say keep the controller for one reason, it's tough as hell. you don't have to use the bell's and whistles, but Lyen beefs em up proper, so when you abuse it going full throttle on a hill, the guts of this controller much less likely to melt. I've put 6000 watts through my 12 fet with no problems yet.
If you really don't want it though, Edward will take it back if you haven't used it.

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Well, I was thinking I should move up to one of the 24 fet infinions, but if you've never had any problem running 6000w through one of his 12 fet controllers I suppose I should be fine with the 18. What voltage are you running at? I got the impression that the controller I have really should be running at "72v" but I'm not really sure if that means 72v nominal, and a max of 91v at full charge should be fine, or if I should be running with a full charge of 72v.

The controller should be fine at 90volts hot off the charger. I have used mine at 84v for months and months, and there are others on the forum that run them to ~100v I believe the crap out at 104v or 109v, I can't recall which.

Now, the controller is capable of "bursts" up to that wattage. do not run it like that for long. I can climb a hill at 72v under load, and the wattage starts at 6000, then rapidly drops to 3000 once I hit 10mph or so. So, 6000 to 3000 in the space of 5 seconds, then I've climbed for about a minute at 3000, but then I run out of hill and it levels off to 1200-ish on the flats. This is harder on the phase wires going into the motor than anything else on my setup. they get hot, but not burning to the touch, so I"m not doing anything about it at the moment.

aaronski said:

The controller should be fine at 90volts hot off the charger. I have used mine at 84v for months and months, and there are others on the forum that run them to ~100v I believe the crap out at 104v or 109v, I can't recall which.

Now, the controller is capable of "bursts" up to that wattage. do not run it like that for long. I can climb a hill at 72v under load, and the wattage starts at 6000, then rapidly drops to 3000 once I hit 10mph or so. So, 6000 to 3000 in the space of 5 seconds, then I've climbed for about a minute at 3000, but then I run out of hill and it levels off to 1200-ish on the flats. This is harder on the phase wires going into the motor than anything else on my setup. they get hot, but not burning to the touch, so I"m not doing anything about it at the moment.

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Yeah I was actually just looking at that myself. I've got what appears to be a beefed up 5000 series crystalite hub that was produced for scooter and moped applications (seems to be a bit heavier and wound for higher speeds, but otherwise identical), so I'm pretty sure the motor itself will be able to handle more than what I can dish out, but the wires running into it do make me a little suspicious. I figure if I run a high voltage I don't need to pull as many amps to hit my desired wattage though, which is one of the reasons I'm leaning towards the 24 cell setup. Of course adding more battery weight is going to take its toll under acceleration as well, so I suppose its all a trade off one way or the other, but I'd rather err on the side of oversizing my pack than undersizing it.

Indubitably said:

aaronski said:

The controller should be fine at 90volts hot off the charger. I have used mine at 84v for months and months, and there are others on the forum that run them to ~100v I believe the crap out at 104v or 109v, I can't recall which.

Now, the controller is capable of "bursts" up to that wattage. do not run it like that for long. I can climb a hill at 72v under load, and the wattage starts at 6000, then rapidly drops to 3000 once I hit 10mph or so. So, 6000 to 3000 in the space of 5 seconds, then I've climbed for about a minute at 3000, but then I run out of hill and it levels off to 1200-ish on the flats. This is harder on the phase wires going into the motor than anything else on my setup. they get hot, but not burning to the touch, so I"m not doing anything about it at the moment.

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Yeah I was actually just looking at that myself. I've got what appears to be a beefed up 5000 series crystalite hub that was produced for scooter and moped applications (seems to be a bit heavier and wound for higher speeds, but otherwise identical), so I'm pretty sure the motor itself will be able to handle more than what I can dish out, but the wires running into it do make me a little suspicious. I figure if I run a high voltage I don't need to pull as many amps to hit my desired wattage though, which is one of the reasons I'm leaning towards the 24 cell setup. Of course adding more battery weight is going to take its toll under acceleration as well, so I suppose its all a trade off one way or the other, but I'd rather err on the side of oversizing my pack than undersizing it.

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when sizing a pack, don't forget that 48v10ah is the same at 100v 5ah in terms of Watt hours available. at the same given speed, you should get about the same milage(and have the same weight) on either battery design. and this would be easier on the phase wires as you mentioned, but in reality, you'll set the amps sky high, have high volts and just go WoooHoooo as you haul ass down the street.

Also remember that changing the pack voltage doesn't change the voltage/current on the motor side of the controller for the same speed/power. It just changes the controller input voltage/current and higher voltages cause lower duty cycle PWM and are a bit less efficient for the controller. Higher voltage/lower current are more efficient for the wiring and connectors. Higher voltage packs also raise the top speed of course and provide the capability of going to higher power (with the attendant possibility of melting things).

To reduce motor current requires higher turn motors. This increases the efficiency of the controller, wiring to the motor and connectors but it limits top speed.

Hey, Alan, how does that work?

Lets say I have 72v pack running drawing 10 amps from the battery, thats 720 watts of power, and I'm at 1/4 throttle cruising at 15 mph. I was under the impression that the controller would convert 72v dc to a 3 phase AC wave at 72v, and use PWM to turn it on/off rapidly to clip the amps to whatever my motor needs to run at that speed.

Am I wrong? is it converting it so 36v at 20 amps to match the KV winding of the motor at that speed? or something else entirely?