Electric Bikes - lifepo4 charger recommendations
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I'm converting over from sla to lifepo4, and was wondering if anyone could recommend a good "fast" charger. My setup is two 16 cell batteries in series.
From the stats found here...
It sounds like I need a 28.8v charger with an auto shut off (non-trickle) feature. Most of the chargers I've found via google mention the number of cells, though. So I want to make sure I don't ruin them by getting the wrong thing.
Thanks in advance!
03-03-12, 06:21 PM
I'm wondering why you wouldn't be considering the charger that is sold to match your pack. I didn't read anything about these packs having a LVC or HVC (BMS) protection. The charger they sell says it's a BMS charger. Without a BMS or some type of protection you are truely flying blind and there is no way to know what each cell is being charged to. So some cells could be over charged while others are under charged. I highly recommend you consider how you are going to protect these cells from this problem and from over discharging.
I use this charger but I have also used cheap 24v SLA chargers and 12v automatic chargers (when not series connecting 12v packs). SLA chargers will actually do a good job. The problem is a way to balance the cells so they are all charged to 3.65v. This is why I say you need a BMS or some way to balance the charge. You can also get single cell chargers that do a nice job balancing the pack.
I did buy one of ballistics bms chargers actually. And you're right, a bms charger is great for maintaining a healthy battery. But to use it, i'll have to partially disassemble the bike/battery pack. I'm looking for a safe 24v charger I can use during times when cannot disassemble the bike. Most of the 24v sla chargers I've found so far have desulfate modes, and don't power off when the battery's reached full charge. The only sla charger i've found so far that might work is the battery tender 24v. No desulfate mode, but it won't shut off, so i'll have to keep an eye on it.
03-04-12, 01:33 PM
I have a 12v battery tender on my motorcycle battery and that will not work for you. It's not so much the fact it won't turn off but it does not charge to a high enough voltage for lifepo4 batteries. It will only charge to 12.7v which is the actual full voltage of a lead battery. The charger that I gave a link to will turn off at 29.2v and is considered a "smart" charger. But chargers like this no mater how much you pay are intended as a "bulk" charger. Meaning they do not care how much voltage they pump into an individual cell. All they care about it the total voltage of the pack. Hence the problem of over charging some cells while under charging others. That's why most people use a BMS to regulate how much voltage each cell gets charged to.
An alteritive to a BMS is semi manual or all manual charging. For example, I used to bulk charge to a given point and then change to individual cell chargers to balance the packs. I now use CellLog8s to monitor the voltage and automaticly turn on/off bulk charging and individual balance chargers. I also use CellLog8s to monitor the cells while riding to prevent over discharging any cells.
Bottom line you need to decide how your going to deal with cell protection on both LV and HV or you will kill those pack.
First off, thanks for the help! According to my voltmeter, my 12v battery tender plus charges at 14.8, then floats at 13.3. I was hoping the 24v version would charge at 28v, which would work good for my lifepo4's.
If not balancing the cells was instant death, these packs would be dieing in a week in motorcycle applications. It's not like motorcycle charging systems have the capability to monitor the individual cells. Unless I'm missing something... Regardless, bms is ideal of course. I just can't seem to find one that will work in my application, of two 12v 16 cell batteries wired in series. I can find plenty that will work with fewer then 16 cells. But none that'll work in my 32 cell setup.
03-04-12, 08:20 PM
Y (http://batterytender.com/resources/frequently-asked-questions)esI agree with you on the battey tender. I was only refering to thefloat voltage. For whatever reason my tender is floating at 12.7v.
In any case I'm not trying to be a "know it all" onlifepo4 cells (I'm far from it). But I can tell you there arecompanies selling so called lifepo4 replacement for lead batteriesfor both cars and motorcycles. Some of them are properly equiped withcell protection and others are not. I almost learned the hard waybut called the supplier.
High end life cells (if matched) will generally stay closelybalanced for long periods at a time. But eventually they all come outof balance and need attention. The same goes for discharging. Withoutover discharge protection you can very easily kill a cell or completepack.
I'm not saying that the cells have to be perfectly balanced butthey should be resonablly close to each other for longest life. Asthe cell drift further apart some cells will hog the voltage causingthem to over charge while the others are undercharged. This not onlylowers pack capasity but puts cells at risk of dropping below a safevoltage under heavy load.
It's your money but I would recomend contacting the supplier andconfirm if they are equiped with cell protection and exactly how theyare protection the cells.
I know your planning on 32 cells but I'm confused as to what youractual final voltage is on your setup. So what is your final voltage?I'm asking because I had a bike running 48v using 2 24v packs. Sowhile I ran at 48v I charged at 24v. So could you do the same?
This won't be the least expensive solution, but it will be by far the most versatile with plenty of other uses if you use rechargeable batteries of any kind. You could get a hobby charger and power supply. This will allow you to charge almost any battery chemistry and balance any time. Mostly the idea with these is to balance on the charge cycle...
03-05-12, 10:38 AM
This is an excellent topic, as i've been having trouble finding a fast yet safe lifepo4 charger for a 48v pack
all the ones i've found are for hobby RCs and 6 cells, and all the ones that are compatible for 48v or 36v are slow chargers
ideally i'm looking for a lifepo4 charger that can get me a good charge in 30 min, as in it doesn't need to be 100% charged, but at the very least 60+%
I'd integrate the charger on the battery bag pack, so i can carry it with me when i go into say McDonald or something like that for a quick recharge, while i recharge myself with a meal as well :D
You can do up to 24s with two Hyperion 1420i chargers and two large power supplies. This would have 1100W charge capability but would require two separate standard 15A circuits to avoid tripping a breaker. :) All this won't fit on a bike very well either, but charging would be fast...
03-05-12, 04:35 PM
thanks rscamp, that one seems pretty good for my purpose, but that means, i'll probably have to build my own "pods" of lifepo4 batteries to charge at least 2 pack of them together at the same time
(originally i was planning to order those PING's lifepo4 packs from ebay, and save myself the trouble to build and solder those on my own, and find a compatible BMC for the packs, etc)
i saw the youtube video of that charger, it was very informative, however i still have a question, you mentioned it can do 550w x2 with 2 separate circuits
now by that you mean the circuit from the wall-plug?
or you are referring to 2 separate power supply so each one will deliver 550w?
The project "bike" i'm setting up is more a Trike than a Bike, so finding space for the whole setup shouldn't be too hard, rather the weight is the only thing i'm concerned about.
- - - EDIT - - -
so i was reading this topic over at http://endless-sphere.com/forums/viewtopic.php?f=14&t=28934
and seems like this PSU might be a good option http://www.ebay.com/itm/MW-24V-DC-25A-600W-Regulated-Switching-Power-Supply-/380416985540?pt=LH_DefaultDomain_0&hash=item58929e89c4
or i could probably modify a couple of computer server PSU to do the trick, which are more affordable and easily accessible to me
i'll probably use 2x 800w PSU or something along the lines, maybe even 2x 1100w if it can make it charge faster
hmm... that's an interesting topic, so it seems like iCharger 3010B 1000W (http://www.hobbyking.com/hobbyking/store/__11597__iCharger_3010B_1000W_10s_Balance_Charger.html) is even better, and the Hyperion 1420i could develop bugs after a while
uhhh... after some more reading found this hot PSU Turnigy 1080W 220~240V Power Supply (13.8V~18V - 60amp) http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=20612
i wonder if that is enough to power the iCharger 3010B 1000W
either way that's what i find the most complicated thing about using lifepo4 batteries, yet they are the only ones that can recharge fast safely and can be recharged often before having to replace them again, and having to calculate how to pack your batteries to match the charger charging capabilities.... this notion is definitely new to me
i never had to bother with that before, and now i cracking my head open just to figure out the best setup, for a quick charge, yet still able to come up with 48v for a 500w motor to last me a decent ride before having to make a pit stop for a quick charge again.
that's the nice benefit of lifepo4, all the previous non lifepo4 batteries and charges takes average 4 hr to charge, and that is simply waaaaaaaaay too long if you are stranded outside, and did not bring a spare battery with you.
that's the whole thing i'm trying to avoid now with the new setup, a fixed regular pack to power the normal stuff, and then the lifepo4 "backup" battery pack
in an analogy the lifepo4 backup battery pack will be like the gallon of gas tank that you will always carry with you for long trips in the wildness far from any gas station ;) and as such i wan to be able to refill it quickly the first power outlet i come across with so it wont run out before reaching home or wherever i wanted to go
- - - EDIT 2 - - -
just finished watching a video of the iCharger 3010B 1000W in action http://www.youtube.com/watch?v=ZwS95pEALHg
and i think i'm in love :p that's pretty close to what i want to setup, now i just need to figure how to pack the lifepo4 batteries to make good use of the 10 cell monitor
in other words now i need to find larger lifepo4 batteries that can hold more power and attach them in series, as having several small packs of 10 will defeat the purpose of fast charging
03-05-12, 06:36 PM
For those of you that have cell charging protection installed on your pack these are very good chargers to consider. And as you can see they come in a voltage ranging from 12v @ 6a all the way up to 84v @ 15a. Their not cheap but their not expensive ether. If you consider one of these chargers and your pack is equiped with a BMS you may want to contact the BMS manufacture to be sure a "smart" charger will work with your BMS.
A few comments:
I misspoke - two 14s chargers ganged would of course be able to charge 28s.
Unless the power supply is particularly high quality, it should be sized to only about 80% of its rated capacity to avoid issues with unwanted thermal shutdown.
Consider that the charger efficiency and power supply efficiencies need to be accounted for when determining the load on the house circuit. Hence the need to split between two with the 550W chargers running near full capacity.
Power supplies with active PFC will consume less power from the wall.
Consider the convenience and reduced risk of making a mistake using a charging setup that doesn't require 'rewiring' the batteries for charging.
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