Oset Batteries Lithium (LiPo) Conversion Directions

[gwhy]

First - thanks to all who have contributed so far on this thread, so much information, actually that is my problem - I'm confused by all the variations and am really looking for help to define a sensible repeatable setup (for 36V Osets) that folks like me can easily understand, shop and put together. I'm more mechanical than electrical so please be tolerant of any stupid assumptions I make.

We have a 2010 36V Oset and the main issue I want to overcome is range, I really need about double the life I currently get from the SLA's with probably 30 charges on them (properly charged initially and seem to be holding close to original range). I can then have my son come with me on the trial loop without concern for getting back.. I'm happy to convert to Lipos. From what I have read:

Batteries: To convert to LiPo and to give the existing range - 6 x 3S1P15C 5000ma (3 batts in series giving 33V) and the 2 banks in parallel giving me 10ah. I could replace 2 x 3S with a one 6S (this reduces the connectors but (I think) may complicate charging (more later). To increase the range I could add further banks of 3x3S1P 5000ma. Each 5ah layer would be 150x143x23 mm and cost about US$75 from HobbyKing, the weight saving is huge - standard OSET batts setup is 10ah weight 9.1kg, LiPo is 2.7kg per 10ah.

Question - Is there a heat issue with stacking the batts, as each layer of 3 batt in series would fit nicely in a hard sealed case in the OSET battery compartment and they would be 3 or even 4 layers deep (20ah!) and assuming a continuous but variable use.

Setup - Discharge (riding)

I would replace the batt connectors with XT60 and use the series connectors on each layer (33v and 5000ma) and parallel connectors to connect the layers to get to 10, 15 or 20AH capacity. I would then need to change the current bike power connector to XT60 and disappear into the sunset, but..... charging.

Setup - Charging

I don't want to have to remove or disconnect the batteries to charge them. I understand the fire issue but am prepared to buy a charger that manages voltage/current/shutoff - which I assume should reduce this risk considerably. So - I have 6, 9 or maybe 12 3S1P batteries all connected in a sealed box and ending in one XT60 connector carrying 33V. Each battery has a +ive -ive and a balance plug for use when charging. This leads me to believe the only way to charge these batteries will be with a separate charging circuit as I haven't seen a 33v charger and I haven't connected the balance plugs to anything yet.

Hobby King have a Parallel Charging board ($8.99) "Our very own in-house designed and built parallel charge board! Now you can charge SIX (2~6S) lipo packs with same capacity & cell count simultaneously with this parallel charging board. That means you can charge 6 3S 2200mAh or more at the same time with a standard charger!" (The same cell count was what made my decision about using all 3S rather than a mix of 3S and 6S).

Question - Can I branch the discharge circuit from each battery to create individual charging circuits that would terminate with XT60s (with it's associated balance plug) on the case cover, leads would then connect to the external parallel charging board and the charger? Or is there a simpler way to do this?

Question - Having got to the point where I have the ability to charge the batteries (my assumption), what charger would be recommended, assuming that it would need to charge 9 or 12 3S1P 15Cs through 2 parallel charging boards. I should add that I'm not planning on charging in the field but back home unless it is fairly simple and I don't have to rewire my minivan to make this happen in the field.

I hope that through all this, with your help I can maybe get to a diagram, shopping list and instructions on how to easily improve the performance of these excellent bikes. Thanks in anticipation !

It looks like you have a good grip on what needs to be done and are asking all the correct questions.

There will be no heat issue with stacking the batts ( if the 15C's battery's get remotely warm on these bikes then there is a serious problem that needs to be sorted )

With a 24v bike it is a little easier just use 6s gives you 22.2v ( 25v hot off the charger ... perfect and easy to charge with 1 charger and one connection) but with the 36v bikes it takes a little more thinking about. Two 5s lipo (in series )will have a voltage hot off the charger of around 40v which is a fair bit higher than the 36 volts needed and two 4s lipo (in series) will be around 32v hot off the charger and thats a little low, If it was me I would go with the 5s battery's and use 2 chargers as the hot off the charger voltage will drop very quickly down to around 38v. 3X 3s will be perfect but at a cost of making the charging a little more complicated also more inter-connections to go wrong. If using 3X 3s the easiest way is to use 3 chargers ( 1 charger for each set of 3s ) these 3s can be as many as you need paralleled up or the same with 5s but with 2 chargers. If you configured the connector into the controller ( i.e 3 connectors for a 3s setup or 2 connectors for a 5s setup ) in such away that this is what connects the the battery's in series when plugged into the bike, when the battery is not plugged into the bike there will be 3 connectors from the battery ( each connector is a 3s battery that can be charged with a standard lipo charger)

Charging your built up battery: balancing the whole pack should not need to be done every time you charge the battery, but very important to balance a new pack before use ( Both my 6s2p have around 30 or 40 charge cycles on them and the cells are still balanced ( but I do check about every 5 charges ) If a cell in a pack is going out of balance quickly then its more than likely there is a bad cell in the pack. So what I'm saying is don't worry about the balance taps and having to connect these up every time you recharge your battery ( just check once in a while ). When building a battery pack balance the individual packs before you parallel them, once all the individual battery's are balanced then parallel the balance taps ( so you have one set of balance taps for each bank of 3s ) I hope this all makes sense.

[mikedufty]

Starting to get a better idea of how the lipos perform. Longest ride on them yet, my kids took turns and totalled 12.5km bike was still going OK but not as spin happy as fully charged.

Charger reported 6700mAh in (nominally 10000Ah capacity) Min voltage was 22.5, so averaging 3.75v per cell, so could possibly have got a fair bit more out of it. The originally batteries were pretty feeble after 6 or 7km, so this is a good improvement.

(this was pretty easy riding, 2km to a park and back, plus heaps of laps of a pretty flat park with a couple of ramps, mainly paved).

[gwhy]

For maximum life expectancy for lipo's, avoid discharging below 20% capacity, so leave at least 2Ah of charge in the battery if its 10Ah, never totally discharge lipos as this can damage them permanently. A well looked after lipo battery should be good for 200+ recharges before the capacity starts to drop.

[mikedufty]

Thanks for that. Mine would have been about 33% left, so getting close. I guess I need to get a power meter if I'm to manage it properly. If it starts to get close more often I'll probably buy some more batteries though.

[ninefives]

Thanks for the info guys. I'm building a simple diagram and shopping list based on 5S 10 and 20ah solutions - I get the relative simplicity of that config!, but a couple more questions:

I plan to end up with 2 x 18.5v 20ah connectors outside the battery case each connected to 4 5S batteries in parallel. Serial connector then gives me 37v and 20ah - fantastic!!

For charging, I remove the serial connector (I'll make the serial to the bike connection permanent to prevent mistakes). So I have 2 banks of 18.5v cells (20ah) to charge (each one 4 5S batts). Its at the point my brain breaks (again).

Which charger should I use? I'm confused by the assortment available at Hobby King. I'm not looking for the most economic if that compromises the life of the batteries or safety. Input AC, a charge time of under 2 hours ideally. Recommendations?

Every 5 charges or so I can undo the case and plug the individual battery balance plugs and power plugs into a "Parallel Balance charging Board for 6 packs 2~6S (XT60)".

What other monitoring equipment is really essential? I remember some previous dialogue that suggested that the bike isn't going to move much before we get to the 20% lowest safe remaining charge. Is that knowledge enough?

Edited October 29, 2011 by NineFives

[betarambo]

So I kind of started this thread and then walked away. Sorry about that. I have been watching the thread but life sort of took me away a bit. First I got distracted building the tallest Subaru WRX in the US (think combining redneck with rice rocket) and then my wife had some health issues. We are now 104 days into her hospital stay, 9 days after her bone marow transplant and maybe two months away from going back to our side of the country.

I was very happy to see that a couple of people who know more about this than I do jumped in here and provided some really good advice. It looks like quite a few people have made the leap. I thought I would update with you with what I have done and maybe answer some of the quesstions.

Charging:

If you are new to this I recomend experimenting a bit. You don't really know how into it your kid or you are going to stay. I would buy a single cheap charger that charges your batteries one at a time. Even the cheap ones are plenty safe. After that you will get to know things more and feel more confident in specing out a charger or chargers that make sense to you.

You do indeed need some sort of DC source. I use the battery system on my camper since in my case it is either at home or at the trials with me. I installed a charging outlet on some 10 guage wire so that I can set the batteries and charger on a stand away from the camper just in case I have a "thermal event". I have three 12V gell cells in paralell in the camper that get charged by a 75 amp converter. When I am home the camper is plugged in so I get plenty of juice. Even when I am camping I sometimes charge all four 6S1P packs without plugging in or running the generator, but I bet it pulls a significant charge out of my house batteries.

For the simplest case I think charging of of you car or van is fine but I would either have the engine running or make sure I have someone around to jumpstart me until I get the feel for it. I would start with this as it is cheapest and simplest until you get your feet wet and get a feel for what you really need. Make sure to be careful when hooking up to the car battery. Just like a jumpstart, a spark near the battery can potentially lead to an "energetic themal event" in your face. I hook the positice up first and the n hook the ground somewhere away from the battery.

If you want to charge at home from AC you will need a converter. The idea of using an old laptop supply is a good cheap one, but keep in mind that these won't put out a ton of current so they are not perfect for fast charges. However, if you are only charging at home you are probably not in a big hurry.

I got my fire proof bags a while back. I use on to charge, one to store, and one in the bike. It is certainly overkill, but for the price a little piece of mind is cool.

36V in a 24V motor:

I think I posted this before, but in general it makes the bike way fast but very poor on traction. We pretty much don't use it this way anymore.

A coutionary thought:

These bikes are dangerous in a different way. They are fun for adults to ride and they tend to handle it. I bought a TY80 a few years a go with some buddies and we started having a TY80 championship the day before each event. This gave us the idea to start riding the osets a bit. The other day one of my buddies who shall remain nameless went to do a wheelie on a 36V bike and looped it. It happened too fast to react and he broke his tailbone. So it is probably best to leave these little wonders to the age group they are designed for or at least know what you are signing up for!

My duaghter won her first junior championship this year so we are going to start trying the adult beginner class soon with 3 full loops and 8-9 sections. I should get some better run time results for you soon. I also put in one of the watt meters which works pretty slick.

In summary, my key recomendation is to start with lipos slow. Buy the minimum, put it in and use it. After that you will start to understand better and then you can get fancy with containers, battery packs, multichargers, and charging in the bike.

[gwhy]

I plan to end up with 2 x 18.5v 20ah connectors outside the battery case each connected to 4 5S batteries in parallel. Serial connector then gives me 37v and 20ah - fantastic!!

For charging, I remove the serial connector (I'll make the serial to the bike connection permanent to prevent mistakes). So I have 2 banks of 18.5v cells (20ah) to charge (each one 4 5S batts). Its at the point my brain breaks (again).

Which charger should I use? I'm confused by the assortment available at Hobby King. I'm not looking for the most economic if that compromises the life of the batteries or safety. Input AC, a charge time of under 2 hours ideally. Recommendations?

I would recommend 2 of these they are what I use and have been very reliable ( I have 4 of them ) http://www.hobbyking.com/hobbyking/store/__7028__Turnigy_Accucel_6_50W_6A_Balancer_Charger_w_accessories.html with the config that you are going for that way you can treat each bank of 5s as separate battery's and havin 2 chargers will half the charge time. You will also need 2 Mains laptop psu's These can be got from e-bay output voltage anywhere between 12-18v and a min current of 5A something like this http://www.ebay.co.uk/itm/15V-5A-AC-CHARGER-ADAPTER-TOSHIBA-TECRA-M1-M2-M3-M4-/150561700685?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item230e2d3b4d#ht_2944wt_1008

Each of these chargers will charge a 5s pack at around 2.7A per hour so a totally discharged 20Ah pack it will take around 8hours to charge but in real life you should never fully discharge a lipo so the actual time will be more like around 6hours

The biggest charger that will do the job is this one http://www.hobbyking.com/hobbyking/store/__11340__TURNIGY_MEGA_400W_Lithium_Polymer_Battery_Charger.html

This will charge a 20ah 5s battery in around 1 hour but you will need a very meaty mains psu to power it ( 30A 12-15v) you could make a charging harness to parallel both your 5s packs when charging and this will give you the 2 hour charge time that you are after with just the one charger.

Every 5 charges or so I can undo the case and plug the individual battery balance plugs and power plugs into a "Parallel Balance charging Board for 6 packs 2~6S (XT60)".

What other monitoring equipment is really essential? I remember some previous dialogue that suggested that the bike isn't going to move much before we get to the 20% lowest safe remaining charge. Is that knowledge enough?

A good all round piece of kit is a watt meter http://www.hobbyking.com/hobbyking/store/__10080__Turnigy_130A_Watt_Meter_and_Power_Analyzer.html this will give you a form of fuel gauge for your battery it will also record amps and volts and it is really usefull for getting the max performance (tuning a E-Bike )

Betarambo made some very good points, It will be best to start with a basic setup i.e 10Ah battery and 2 smaller chargers ( for simplicity ) until your happy with how the lipos work. maybe even go with 2 10ah battery packs rather than 1 20ah battery, not even thinking about the safety aspect of such a powerful battery but also think of the cost, should you accidently destroy a 20ah battery all in one go.

Edited October 29, 2011 by gwhy

[ninefives]

Again, thanks to everyone for the technical advice and the common sense. I'm going to build a 10ah "cassette". That way, I can in the future build another to either swap or piggy back with a couple of parallel leads to get the 20ah distance. So my shopping list currently looks like:

Hobby King

4 x 5000ma 5S1P 15C Zippy - (2.8kg) $160 (ordered a spare, as DOA likely)

1 x Nylon XT60 Connectors Male/Female (5 pairs) $3.19

- 4 x Female replace the ones on the batteries

- 1 x Male replace the OSET power connector

- 1 x Male and 1 x Female for the power meter

2 x XT60 Harness for 2 Packs in Parallel $4

1 x XT60 Harness for 2 Packs in Serial $2

Pack of 3/16th (4mm) shrink tubing

1 x Parallel Balance charging Board for 6 packs 2~6S (XT60) $9 (not sure this needed yet)

2 x Turnigy Accucel-6 50W 6A Balancer/Charger w/ accessories $46

2 x Lithium Polymer Charge Pack 25x33cm JUMBO Sack $5.46

1 x Turnigy 130A Watt Meter and Power Analyzer $24 - On backorder so bought an Eflight Power Meter rated at 120A from my local RC store ($50). This is essential equipment.

Note that HobbyKing doesn't send manuals, web search them.

My miscellaneous shopping list is:

Battery Case (cassette)- used Lock n Lock Food Savers 800ml/27oz

Laptop power supplies for the chargers - This hasn't worked for me they produce 19v, the chargers accept 10v-18v - use a 12v battery hooked up to a charger.

3mm padding (between and around batteries) - Wrapped the batteries in rubber antislip matting.

Zip ties (hold the batteries together) Not required in the food savers.

Grommets to seal around the parallel cables exiting the case - used silicon sealant

Strapping to hold the cassette in the tray - essential - used the old battery bag - not ideal.

Follow-up notes:

Awesome upgrade - some important considerations around LiPo safety. If you are considering this upgrade, then read this extremely important information http://www.rcgroups.com/forums/showthread.php?t=209187

Stuff arrived in about 10 days. I ordered 5 batteries just in case, and one arrived with a cell out!.

Soldering on the XT60 connectors is challenging to begin with, I had to upgrade to a 100watt soldering iron, a gizmo to provide an extra pair of hands, used old style lead based solder. Use the Allen Key heat sink or the plastic melts. Excellent how to video here http://www.youtube.com/watch?v=3Yj-DHxKS6c.

I cut a 3/16th x 3/4in slot in the side of the food savers to allow the cables to exit. Work out where by dry fitting the food savers "cassette" to the battery box on the bike.

Each cassette holds 2 batteries wrapped in the rubber matting very neatly with the XT60 connector just on the outside. The cassette fits across the bike battery case very snug!

I fitted the power meter into another Lock n Lock 180ml/6oz.

Fit the power connectors to the bike into another small Lock n Lock to waterproof.

Findings:

The RC world rates batteries at their minumum voltage, so my 5S1P batteries are rated at 18.5v but when fully charged actually have 21v - so I have ended up with 42v when fully charged - bike speed is up noticeably but motor does not get warm. DO NOT allow these batteries to fully discharge, a safe minimum seems to be 37.9v (30% life remaining) go beyond that and you could destroy the battery. This is where the power meter comes in, mine shows voltage and mA used. For my 10Ah setup I stop at just before 7000ma used. Currently the bike seems to consume 90ma per minute so a working range of 75 minutes. There is no significant loss of power down to that threshold. (Update - blasting around for 30 minutes flat out used average 125ma per minute so range to 30% remaining 55 minutes and to 20% remaining absolute lowest 63 minutes). Trials playing in the yard 50 to 80ma per minute.

Always disconnect the batteries from the bike and power meter so there is no drain while in storage.

Charging - This is where the move from the super safe lead acid to LiPo gets serious. These batteries can be dangerous - if you haven't read the link on safety, read it now. It seems that there are 2 main dangers: Charging at the wrong voltage and physical damage. The charger I have checks the battery, reads the number of cells and says what it finds, then asks for confirmation. I also charge them in a clear space on concrete in a Lithium Polymer Charge Sack and check them regularly and disconnect as soon as they are charged. (BTW LiPos like to be stored partially, not fully charged so the RC folks tend to charge them on the way to their event).

Physical damage - these batteries are not well protected, at one end you can see the individual LiPo cells with a soft foil like material, a nick in this and you will get a fire - but not immediately, just after you have stored the bike in the truck/car and gone off for "refreshment". Hence my wrapping them and putting them in a cassette. Look at your current SLAs and see the wear marks on the sides where they bounce around in the battery case.

Using my 2 small chargers seems to take 150 minutes to charge the 4 batteries from 40%. I could buy 2 more chargers and halve the time.

555555555

Edited November 23, 2011 by NineFives

[frogger]

I am very familiar with using lipo batteries in RC applications and would love to build some packs for the Osets. When using lipo in my RC cars I would never consider using without low voltage cut offs because of the dangers associated with a discharged lipo. Has anyone found a reliable lipo low voltage cut off device that can be fitted to take the guess work out of running the packs down?

The ones we normally use are tiny little things meant to be used between the ESC and receiver so not ideal in this case.

[gwhy]

I am very familiar with using lipo batteries in RC applications and would love to build some packs for the Osets. When using lipo in my RC cars I would never consider using without low voltage cut offs because of the dangers associated with a discharged lipo. Has anyone found a reliable lipo low voltage cut off device that can be fitted to take the guess work out of running the packs down?

The ones we normally use are tiny little things meant to be used between the ESC and receiver so not ideal in this case.

Im not sure which LVC device referring to but if its reading the total voltage from the pack these are only really any good for small battery packs and will not really protect the battery's, if you really want to use belt and braces then you really need to monitor at cell level through the balance taps, there are cheap devices that can do this but do not shut the battery down if there is a problem it will only sound a alarm if any one of the cells drops below a pre-set voltage. I dont use cell monitoring myself on my packs as I think connecting and dis-connecting the devices to the tiny balance leads is even more of a hazard, but I did built myself a very accurate digital battery monitor ( total voltage of pack ) that shuts my controller down when my battery's get to a pre-set voltage (around 39v ) and any cells that are going bad will show up when balance/charging them, I also check periodically the state of each cell with in the pack every 3 or 4 charges. So far I have had no problems using lipo packs I have 6 48v lipo batterys that I have been using on e-bikes for over 2 years.

[frogger]

We race electric RC at national level so we are near anally retentive about our cells. We monitor at the cell level + balance our packs every charge. These days our ESC's can be set for different cell types (NiCd, NiMH, Lipo, Life, etc.) and have built in low voltage cut off that can be adjusted at 0.1v increments. We used to use standalone LVC's from Novak, Cellpro, etc. but they are no longer required due to the ESC having it built in.

It doesn't matter too much if you monitor at overall pack voltage as long as you balance your cells regularly. You don't normally set the cut off to kick in at the lowest possible point, you set it incrementally higher so that you have a buffer. We have done many tests amongst flyer friends of ours who use 4 - 6 cell packs, some of them will fly with their packs the whole season long without balance charging them and then when we stick them on the balancers they end up near perfect or maybe one cell will have a 0.2v difference over the span of 13 month regular charging. It's not guaranteed but that is what we have seen.

I'll do a little more research myself but ideally I would like a hard wearing, waterproof LVC I can plug in between the pack and controller that will sound a buzzer when it reaches a pre-set overall pack voltage so that my kids know when it's time to head back. I don't even want to have to think about it.

Even better would be if Oset can build it into their controller.

[gwhy]

We race electric RC at national level so we are near anally retentive about our cells. We monitor at the cell level + balance our packs every charge. These days our ESC's can be set for different cell types (NiCd, NiMH, Lipo, Life, etc.) and have built in low voltage cut off that can be adjusted at 0.1v increments. We used to use standalone LVC's from Novak, Cellpro, etc. but they are no longer required due to the ESC having it built in.

It doesn't matter too much if you monitor at overall pack voltage as long as you balance your cells regularly. You don't normally set the cut off to kick in at the lowest possible point, you set it incrementally higher so that you have a buffer. We have done many tests amongst flyer friends of ours who use 4 - 6 cell packs, some of them will fly with their packs the whole season long without balance charging them and then when we stick them on the balancers they end up near perfect or maybe one cell will have a 0.2v difference over the span of 13 month regular charging. It's not guaranteed but that is what we have seen.

I'll do a little more research myself but ideally I would like a hard wearing, waterproof LVC I can plug in between the pack and controller that will sound a buzzer when it reaches a pre-set overall pack voltage so that my kids know when it's time to head back. I don't even want to have to think about it.

Even better would be if Oset can build it into their controller.

If there is enough interest I could do a limited run of the lvc that I use ( or just post up the circuit and code for people to build there own), I dont know the configuration of the controllers that oset use so it will not shut down the controller ( do they have a e-brake connection on the oset controllers ? ) but it could have a alarm, at the moment the one that I use there are 2 leds for a visual indication of SOC of the battery, steady green , flashing green, steady red and flashing red ( 4 levels of monitoring )if flashing red continues to flashes for more than 5sec then the lvc shuts down the controller.

[frogger]

I'd be interested. Any more details/pics?

[gwhy]

I'd be interested. Any more details/pics?

The lvc that I use is powered from the controller's 5v supply and measures the total battery voltage ( my battery is 48v ... not used on a oset ) but with a few additional components could be a stand alone device that can be plugged directly into the battery pack. at the moment the lvc is not adjustable for different voltage battery packs ( the voltage settings are hard coded into the chip that I use but could be re-coded easy enough for different lvc and different battery voltages) I could re-write the code to make it adjustable for different battery packs but this will take a bit of time to test and sort out ( and only really worth doing if there is enough interest for a universal lvc) . The chip that I use is a picaxe08M and a handfull of other small components. my device measures about 30mm x15mm x 15mm and contains 2 leds and one thin multicore wire (4 wires) that connects to the the controller, 2 wires are to power the lvc a wire to monitor the battery pack and a wire to disable the controller. I will take some pics today and try and post them up some where.

[frogger]

My current plan is to go for 6 x 8000mAh 3SP1 packs, 3 in series (11.1v x 3) and then parallel (8000mAh x2) them up which should give me 16000mAh at 33.3v (37.8v charged). I will charge the packs in banks of 3.

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=16225

I already have a great charging system setup for my RC vehicles. It's a high power 12v PSU with 3 x Cellpro Multi4 chargers fitted in a handy suitcase.

Edited January 2, 2012 by frogger