Oset Batteries Lithium (LiPo) Conversion Directions
Posted 16 February 2011 - 12:44 AM
While the benefits are impressive, they do not come free. Lipos have significant risks and require a higher level of technical competence and attention than the stock batteries do. If you are not somewhat technical, willing to learn, and willing to put some extra attention into the care and maintenance of the bike then stop here and enjoy a really cool bike as it is.
Safety disclaimer: I am attempting to relate how I modified my daughterís bike and the things I have heard and read. I make no guarantees about anything including your safety or the safety of your child. Go get educated and then decide on your own if this is the path for you. I accept no liability whatsoever and if you try to sue me I will force you to ride a Reflex for the rest of your trials days.
With that out of the way, most LiPo fires are the result of inattention and negligence. I have never had a fire and donít know anyone who has. I have however read about them on the web. A quick search for ďLipo fireĒ will provide you with plenty of information. It appears that virtually all accidents come in one of two forms; either you charge the battery improperly or the battery sustains physical damage and is not dealt with properly.
To prevent charging fires is simple. Read the instructions on your battery and your charger. Follow the instructions. Fires happen when you hook up a 3 cell battery (11.1V) and set the charger for a 6 cell battery so it shoves 22.2 volts into it. Always charge them in an area that would not allow a fire to get out of hand, never leave them unattended when charging, and have a bucket of sand ready. Putting out a metal fire is not the same as a conventional fire!
To prevent physical damage make sure to mount the battery in the existing Oset tray. It is very sturdy and should protect them from all but the most horrific wrecks. Make sure to secure the batteries in the tray using straps of some sort. I have had good luck with the stock battery bag. If a battery does get damaged with a visible tear or nick in the case beware as the fire can take an hour or more to start. If this does happen, set the battery in a fire safe place a watch it from a safe distance. Read more about this on the web, but I believe they say to dispose of it after waiting an hour by dunking it in a bucket of saltwater and throwing it away. Never continue using a battery that shows signs of physical damage.
Burn bags are cheap insurance for storing, charging, and even when they are in the bike. I have not yet had a chance to test them out as the ones I ordered have been back ordered for awhile, but I think they provide that extra little bit of reassurance.
Configurations: Lipos are made up of individual cells that each are nominally at 3.7V. The configurations are shown as XSYP where X tells you how many cells in series make a set and Y tells you how many sets are in parallel. Generally you are looking for 6S1P for 24V bikes and 8S1P for 36V. I know the voltages donít add up exactly but the batteries are at much higher voltages than nominal when charged and the Oset system is not very picky.
Capacity: The batteries you will be getting are rated in mAH (millamp-hours). The stock batteries are rated in AH. 1 AH = 1,000 mAH.
Discharge: This number tells you how quickly you can discharge the battery. I recommend the 15C variants as they can supply plenty of current but are affordable. The only advantage I can see with a higher C rating is that you could charge the battery more quickly. However, a 15C can be charged in half an hour so there is no justification for the extra cost.
Where to buy
You can buy Lipo batteries at a lot of places. I have spent hours searching and have found no one comes close to Hobby King for prices. They are based in China so shipping is not cheap and it does take time. They do however have warehouses in the US and Europe with some limited stock which can help. If you want to get fancy there are places that can make custom packs for you but the cost is prohibitive. I have found that even though my orders take a while and sometimes documentation is a mess or nonexistent, they are the way to go. http://www.hobbyking.com I spent $138 US total for everything for my first setup including one set of batteries, charger and connectors.
What to buy
Batteries: For a 24V bike buy 2 Zippy Flightmax 6S1P 15C 5,000 mAH batteries. Each battery will put out over 24V (nominal is 22.2V). Buy two of them and hook them in parallel to get to a total of 10 AH at 24V. This gives you the same capacity as the lead acid batteries which are 2 12V 10 AH batteries hooked in series. Some Osets use 14 AH batteries so you might want a third Zippy to get to 15 AH. You may find that they appear to run longer but that is probably because your other batteries are a bit aged and donít last as long as they used to. It might also be because your bike is now 10 pounds lighter. For longer run time you can buy more batteries. Since they are a lot smaller and lighter, you can fit 4 of them in easily and 6 if you got creative effectively doubling or tripling your range. Just make sure to protect them if you start really stacking them up in there as a nick in the case can cause a fire. These batteries are designed for the remote control car/airplane/helicopter/boat world. In that world these are the cheapest batteries around. They work perfect for us since the 15C rating is plenty and they are half the cost of any other brand. Keep in mind that they tend to use up a battery in about 8 minutes whereas we take more like an hour or more, so our needs are much more modest than theirs. For 36V bikes buy 2 8S1P 15C 5000 mAH. This gives a nominal voltage of 29.6 but they should put out more like 33V in the real world. A 9S would be better but I have not found any. A 10S would be getting a bit high on the voltage side but should be fine in practice. I have not done this yet on a 36V bike so anyone who has please post your results. It might be better to use three big 3S1P packs in series. I have ordered a couple of 3S1P packs so I can put them in series with my 6S1P and try 36V on my 24V bike. I am told directly from Oset that it will work fine.
You can buy the 6S1P batteries here (they sell for $45 US):
Connectors: The connectors on these batteries are junk. Since you have to add a connector to the bike anyway you might as well use something good. Also, if you change to some standard connectors the chargers and other things you buy will come with the connectors you need. I use XT60 connectors. Hobby King sells bare connectors, premade Y cables for running parallel batteries, and connectors with flying leads to save you some time. They are pretty cheap so order some spares. Note that when soldering directly to the connector you might melt the plastic body. I use an Allen wrench of the right size in the connector as a heat sink to prevent this. When the application allows I prefer to buy the ones with flying leads to make it a little easier. Some links to connector options:
Charger: You have a few options here. I started with a cheap charger while I learned about it. For about $25 US I got a basic 6 cell 50W charger. The one I picked worked fine and charged a pack in about an hour. I later bought a bigger charger for $80 US that could charge them at 10A (which is 2C in a 5 AH battery). This one does the job in half an hour. They also make chargers that handle 4 packs at once. There is a lot of variety out there so use your own discretion. Make sure that whatever you buy is for LiPo batteries and can handle the number of cells your packs will have. Donít accidently order a charger that only goes up to 4 cells when you have 6 cell packs like I did. Do not try to use a charger that is not specifically designed for Lipos as you will be posting here later about your fire. I always balance charge mine as I think this keeps them lasting long and happy. There is plenty of reading in your chargerís manual and on the Internet about this topic.
Link to the 1 hour charger that worked good:
Link to the half hour charger that works better:
Power Supply: Almost all chargers run on 12V-18V like from your car or camper batteries. I charge mine from my camper so I do not need a power supply. If you want to charge them at home and donít have a handy DC power supply you will want to get one. You can pick one up locally, or Hobby King sells some, or you might have one kicking around in the garage. Note that if you buy the big 10A charger you will need a power supply big enough to deliver the power to the charger. It is easiest to convert everything to watts when doing this. To charge one 6S1P pack at 2C (half an hour charge) you will be pushing around 10A at 24V which is 240W. So you would need a power supply around 250W which is about 20A at 12V if you are pulling from a 12V supply. You may find it best to skip the power supply and charge it off your car or camper at first. Be careful with sparks as you hook up as even lead acid batteries can have fires. I made a connector box on some long leads to hook into my camper without being near the camper batteries. This allows me to charge easily and the length letís me set them away from the camper in case I hose up the charger settings and start a fire.
Burn Bag: I still donít have one yet as the ones I want are back ordered. They are cheap so you probably want a couple for storage, charging and when the batteries are in the bike. You can read the reviews but I think it boils down to a problem with some of them that they use cotton stitches to hold them together and cotton is not very flame resistant. Some people just staple the stitches and they are good to go.
Gadgets: Hobby King has a lot of voltage monitors and such. Some cost just two dollars. You might want to pick up one of these as well for a quick check of charge. You do get what you pay for sometimes so you might find that you are not lucky and the one you get doesnít work. They also sell watt-meters and a bunch of other diagnostics. You donít really need any of this to get started but at the same time these can help you understand how your setup is working. I have a couple of cheap battery voltage monitors that work pretty well and have a watt meter on order to use like a fuel gauge.
Now that your package from China has arrived you have a little soldering to do and some charging. Start by reading the safety stuff.
I clipped off the factory connectors on the batteries and replaced them with the XT60 connectors. Make sure you get the sex correct so you are compatible with your chargers. The batteries get the female side (sockets) and the bike gets the male (pins). Look at the cable that came with your charger to be sure.
Also, be very careful not to short the battery leads. I understand that even a millisecond of shorting will ruin the battery as it will draw more than the 15C rating. The best way to accomplish this is to only clip one lead at a time. Donít clip the second one until the first one is all soldered and sealed. Once the new connectors are on they make it pretty darn hard to accidently short them.
Make sure you get the positive on the right side of the connector. If you bought the connectors with the leads they are color coded so just hook red to red and black to black. Make sure to get a good solder joint as these may have to handle around 30 amps.
Putting the male side on the bike is pretty straight forward. Hook black to black and red to red. You donít have to worry about shorting here as the batteries are not in the system, but do use good heat shrink so you donít have to worry about it down the road.
Charging: Charge up your new batteries following the instructions from the charger. For your first one you can limit the current down to a couple of amps until you feel comfortable. Never charge these batteries past 10A per manufacturer specs. Make sure to set the charger to LiPo mode and get the cell count right. Connect the balance port and also the main power leads. The charger will let you know when it is done.
Installing the batteries: I set the two batteries side by side in the battery tray and hold them in with the factory battery cover. You might want to come up with something more elegant, but this works well for me. Connect the two batteries together with the Y cable you bought to make them parallel. Connect the other end of the Y to the bike connector you installed earlier.
Turn the key on and you should be in business. My daughter reports that the bike is faster. I think it is mostly in her head, but it could be that the other batteries were old. It might also be that I shaved about 10 pounds off the bike.
Another option is to use LiFe batteries. They are similar to LiPo but with a different chemistry. Frankly when I first saw them I ignored them right away as they appear to be the environmentalistís answer to LiPo and I have spent enough time in US Forest Service offices dealing with loony environmentalists. However, I think I heard that they are much safer. I think they have a little bit less performance and a little higher price, but it might be worth it to you. Post back here if anyone tries them. Most LiPo chargers will work with LiFe batteries as they have a specific mode for it.
I wrote all this down as I have had several requests from people in my local club and from forum users. A friend of mine got me started on it so I thought I should pay it back. Thanks to Rick Keffer who figured all of this out and taught me. Iíll try to post some other threads on some of the other upgrades Rick has helped me with like suspensions, wheels and tires.
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Posted 16 February 2011 - 04:56 AM
Posted 16 February 2011 - 01:48 PM
Posted 17 February 2011 - 04:06 AM
Posted 18 February 2011 - 03:23 AM
Posted 24 February 2011 - 07:31 AM
I've just put a Shorai LiFePO4 starter battery in my road bike. I've wondered if they would be an easy upgrade for the OSet too. They claim to be set up to work with a standard 12V bike lead acid charging system, they are similar size to the standard oset batteries, so could possibly just be dropped straight in. I just wonder if they are as good in a power battery application as they are as a starter. Not sure I should trust the oset charger that has already killed a set of Pb batteries with expensive batteries. Shorai market their largest as 18AH pb equivalent, but it seem like they are actually only 6aH. Not sure if their equivalence calculations apply when it is being used for continuous power.
Posted 25 February 2011 - 12:34 AM
My daughter's bike shouldn't be any faster, but she swears it is. I think the old batteries must have been weak.
I just got the 3 cell LIPOs today to run in series with the 6 cells. This will give use 36V so that should make it a bit faster. We'll see how the 24V controller and motor react. They tell me it will be fine. I'll let you know hopefully this weekend if I can get time to do some soldering and let her try it out.
I also got my watt meter so I can see how much juice she is pulling and use it like a gas guage to see when the batteries are almost done.
Posted 25 February 2011 - 09:33 AM
Posted 30 March 2011 - 05:52 AM
Posted 30 March 2011 - 10:29 AM
Do you monitor the cells while in use? How would you do that? A voltage display for each cell doesn't sound practical.
Personally I dont monitor at cell level when using my bike any more, I just monitor the whole pack (44.4v) and stop riding the bike hard when the battery voltage gets to around 40v , you start to get a feel for how well the pack is behaving by how quick it discharges. You can get cell level monitors in different shapes,sizes and functions and I used to use 2x6 cell monitors ( I use 12 cells ) that gave a voltage readout on a lcd screen with all 6 cells ( 12 cells in my case ) being shown at the same time and also has a audible alarm that can be set for a low cell each device was about 2"x1"x0.5" and was around £10.00 each.
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Posted 31 March 2011 - 03:23 AM
I got the 12V batteries the other day to try the 36V setup but haven't tried it out yet. I did at least make the series cable I need for it and swap the connectors on the batteries. We have a trials this weekend so maybe I can try it there. I have gotten distracted lately modifying my WRX for serious off road abuse, but that's another story for an entirely different forum...
Posted 02 April 2011 - 06:44 PM
Hi there, what about something like this...
Would this work ?
It would be a improvement on sla's but only for the weight of the pack, LiFePO4 battery's can not deliver very high currents ( normally 2C about the same as sla's ) over extended periods, The pack in the link say's 10A Continuous discharge and only 25A Instantaneous Maximum Discharge so They are not really ideally suited to be a high performer but the pack will weigh about halve the weight of equivalent sla's and about halve the size you would need 2 of these LiFePO4's packs wired in parallel to really make them worth while on these little bikes . You can discharge them at higher rates but this will make them warm/hot and also make them deteriorate faster, So the extra cost may not be worth while. Where as a small 10Ah 22.2v lipo battery (15C or higher ) pack would be something like 150A Continuous and 300A Instantaneous Maximum Discharge so they should not get hot in use and the weight and size is about a third of sla's.
Posted 04 April 2011 - 10:06 AM
Good stuff, I just put in an order with Hobbyking.
Just thought I will ask, But dont forget a charger as well ( You can not use a normal sla charger ) and also another bit of very good kit from HK is a watt meter
, ( Im sure they do a cheaper Higher spec meter than this one but I cant find it ) This will give you running/pack voltage, AH used, max watts pulled and min voltage drop from the pack. If you want more detailed info on how to use/make the most of lipo's safely then drop me a PM.
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