ElectroCat has been crying in the garage the last months, but will soon be ready to get out on the street again! New batteries, new controller and new battery management system are all ready to be installed.
Picture: A ThunderSky LFP 90 Ah and a 40 Ah. The 90 Ah weighs 3.2 kg (7 lbs) and the 40 Ah 1.5 kg (3.3 lbs). The present battery pack consists of 16 cells @ 90 Ah, the new battery pack will be about 40 cells @ 40 Ah.
When I shipped ElectroCat to U.S.A., I had to leave the battery cells in Sweden. It had been too complicated to ship them because they are considered dangerous goods. But my dad Sven didn’t mind that I left the battery cells in Sweden, he has a couple of EVs too. And because ThunderSky cells are available in U.S., it was a pretty easy decision.
I had imagined to have the bike up and running a couple of months ago, but I had forgotten the rule of π (pi) that says that everything will take at least π times longer than expected. (For you that aren’t a geek like me, π = 3.14). First off, the bike was trapped in customs for a month, before the kind people at Department of Transportation decided to allow the import of it (see earlier post – “ElectroCat has arrived!”). Then engineering school took all available time. Studying business is vacation compared to engineering… A normal math homework takes at least 8 hours, and they are due every Tuesday. And on top of that I have three more classes…
Anyway, I shouldn’t complain, I very much enjoy studying. And now everything I need for ElectroCat is here: batteries, controller and BMS System.
New battery pack
When I had to get new batteries anyway, I took the opportunity to change the battery configuration in an attempt to make the bike significantly more powerful. The present battery pack consists of 16 cells @ 90 Ah and has a nominal voltage of 53 V. That voltage did fit the original motor – the 48 V Briggs & Stratton Etek – but it doesn’t allow me to use the full potential of the new 72 V Mars Etek-RT motor. I can’t fit more battery cells into the bike, real estate is always a scare resource in motorcycles, so I have to change the battery configuration to get higher voltage. With small cells like the A123Systems M1 cells of 2.3 Ah each that KillaCycle’s uses, it is easy to pick any voltage, but not with large cells like the ThunderSkys I use. ElectroCat have only one string of series connected batteries, and to get higher voltage I had to go down in cell size to fit in more cells.
ThunderSky makes cells in all different sizes from a few Ah to 10.000 Ah or more, these giant batteries are for example for submarines. My target voltage was something about 100 V, which is twice the present. Cells of about the half size would give me that voltage with the same battery weight. The plan is therefore to put 40 * 40 Ah cells in the bike, but I am not sure yet if that many will fit. With about 100 V nominal voltage, I can use the full potential of the 72 V motor.
Picture: A box full of goodies….
New Kelly controller
The higher battery voltage requires a motor controller capable of higher voltage. The present Alltrax AXE 7245 can only take 72 V, and it has no regen (regenerative braking) which I would like to have.
Kelly Controller (www.kellycontroller.com) makes nice controllers with _very_ nice price tags. I bought their largest DC controller capable of 144 V and 650 A (boost, 550 A 1 minute and 260 A cont.) About 3 kg (6 lbs) and with regen! With this controller and the new battery pack, the bike should make close to 100 mph (160 km/h) which isn’t so bad for such a small motorcycle. The motorcycle did about 90 mph with its gasoline engine.
The total price for the controller with shipping to U.S. is just below $ 2.000. Kelly Controller really likes racing and electric motorcycles, and I got a very, very generous discount of 50 %. So I only paid $ 1.000 for this lightweight, powerful high quality controller.
Kelly Controller has controllers in all different sizes, from 12 V and up. They also have a few brushless controllers, the largest one is for 144 V and max 250 A. The Kelly Controller online store is definitely worth a visit if you are building or planning to build any smaller EV (scooter, motorcycle or small car).
Picture: The brand new Kelly KDH14651B Controller, capable of 144 V and 650 A and with regen! Only 3 kg (6 lbs).
New Battery Management System
Lithium batteries _must_ have a battery management system. The batteries will be ruined within a few cycles without it, and in worst case you can get a pack fire, especially with the classic lithium metal oxide cells. ElectroCat has lithium iron phosphate cells which are much more stable, robust and safer, but they still need a battery management system to make sure they don’t get over-charged or under-discharged.
The battery management system (BMS) turned out to be one of the most difficult components to get. The selection on the market is very small, and there are nothing really plug-n-play. ElectroCat’s first BMS was two chargers for radio controlled models. The system was full of “spaghetti” (wires to every single cell in the battery) and not very user-friendly. It could only charge with 10 A and a full charge would take about 8 hours, and it required a 12 V power supply that barely could fit inside the bike. The chargers ran on 12 V because they were designed to be plugged into the 12 V outlet in the car so one could charge its electric radio controlled airplane or car out on the field. The system worked, but it wasn’t a very attractive solution.
I will be beta-testing a new BMS system in ElectroCat. The system is not completely “spaghetti free”, but it has much less wires than most BMS systems. One little board is mounted at each cell, and there is a central brain that controls each unit and also controls the charger. The system can by-pass as much as 2 A, which will make it sufficient for as large cells as 40 or 90 Ah. The boards fit from 40 to 90 Ah cells. I am very excited to try this new system out – it looks very promising.
Picture: The new BMS system for ElectroCat. The black little box is the “brain” and there will be one board per cell. The photo shows five of the boards for ElectroCat.
Battery change – a two-step rocket
The battery change and all its complications will be a two step rocket. ElectroCat is in perfect running condition – except it has no battery cells in it.. To get the bike registered here in U.S.A., the bike has to be running. To make sure the bike really will run when I take it to the inspection, I will put in 16 cells @ 90 Ah. But, where do I get 90 Ah cells from? I have only bought 40 Ah cells… I happen to be so fortunate that Bill has bought 60 cells @ 90 Ah for his electric Rabbit convertible, and these aren’t installed yet. I will simply borrow 16 of his cells to get the bike registered. 🙂
When all paperwork is done and the bike has got its registration plate, I can install the new battery pack and controller. To put in the sixteen 90 Ah cells should only take a day or two, but to get the new batteries and the new controller in will be a large operation… I will try my best to report the progress here.
May your batteries always be charged!
// Eva 🙂