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.