Thursday, 19 May 2016

The Perils of DIY Headway LifePO4 Battery Building

The Perils of DIY Headway LifePO4 Battery Building

Here are a few things to watch out for if you are building your own headway pack:

Charge All of the Cells . . . 

A headway cells can read 3.2v and be nearly empty or quite full. So just becuase the volatges are "balenced" it does not mean that the charge levels are.

Use a single cell charger to charge all cells individually to 3.65v. This makes things a lot easier, becuase when you connect up yout BMS, it will not have to do so much balencing.

If you do not charge individually the BMS may takes WEEKS to balence the pack.

Watch that BMS!  . . . 

Do not trust your BMS, headway cells have a low internal resistance apprently so the BMS somthimes gets confused and will discharge your headway cells compleltly which kills them! So after rigging up your BMS, check to see that it is not discharging the cells.

Spending more on a BMS (ie. choosing qaulity) will not prevent this behaviour. Even a high qaulity BMS will do this. I do not understand why, just watch out for it.

Work in a Clear Area . . . 

You will need a screw driver / allen wrench / allen key to put your pack together, also perhaps some pliers etc. Keep these well away from the pack when not in use. If you place you pack on top of a metal object, it will short the terminals and you will get a big flash (which is scary) and also perhaps damage the cells.

Watch Order of Balencing Wires.. . .

The order in which you connect the balencing wires from the controller will differ from BMS to BMS so make sure you get them in the write order. Read the instructions (if you are lucky enough to have any).

Always connect all of the balencing wires to the pack, before connecting the BMS.

Do not buy secondhand . . .

This wholeprocess of headway DIY batteries is confusing enough without using secondhand cells. Some will be bad, and this will cuase problems. . . trust me you will have enough problems.

Conclusions . . . .

Perhaps I am over confident but I have found building my own pack very difficult. I would recommend that you buy a preassessmbled pack, and learn by fixing it when it comes of age. Componenets are expensive and you do not need to damage many befor ethe costs equal that of a pre-built pack.

Save youself the hassle and buy a ready made battery pack.

Environmental Consultants

Using a Step Up Transformer to Run Ebike Motor

Using  a Step Up Transformer to Run Ebike Motor

Swaping from a 24 volt system to a 48 volt? Well that means a new battery . . or does it?

Can you use a step up transformer to turn 24v or 36 v in to 48v?

Yes you can but you may run in to trouble with supplying enough amps.

This is the kind of transformer which can be had on ebay. It is rated at 2000w but the this is a maximum wattage under ideal conditions.

If you were to input 46v anf take out 48v not doubt this transformer would provide close to 2000w but with alarger step up it will provide a lot less . . just 500w stepping up from 24v to 48v.

A 2000w Step Up Transformer Fresh from Ebay

Wiring and Adjustment is Easy - You will need a volt meter

The Transformer would not provide enough amps.
The problem lies in that a ebike motor rated at 250w will use perhaps double this when climbing a hill. A 500w motor such as the one I have will then use 1000w.

This transformer might wrok if you were stepping up fron 24v to 26v on a low wattage motor. But a step up of more than 12v and you will likley have trouble on high amp applcations such a electric traction motors.

Here are the specs copied from the sellers listing on Ebay:

 Output Current: 20A(MAX) More than 18A, please enhance heat dissipation,
 Constant current range: 20A(max)
 Output Power = Input voltage * 20A, such as: input 12V * 20A = 240W, input 24V * 20A = 480W, input 48V * 20A = 960W, input 60V * 20A = 1200W

As you can see the 20a max input means that at a given input voltage the watts are resytcited by the performance of the transformer.

(If you need more power, you can use two modules in parallel, such as the output to 30A, two modules can be used in parallel,the current per module can be adjusted to 15A.)
 Working temperature: -40 to + 85 degrees (ambient temperature is too high, please enhance heat dissipation)
 Operating frequency: 150KHz
 Conversion efficiency: up to 95% (efficiency related with input,output voltage, current and voltage difference.)
 Overcurrent protection: Yes (With current limiting adjustment, adjustable output current limit, current exceeds the current limit, the output current is automatically reduced to a minimum 5A, according to the nature of the load current will be different.)
Short circuit protection: Yes (input 30A fuse) double short circuit protection, the use of more security.
Input reverse polarity protection: None (if necessary, please enter the string into the diode)
Output prevent reverse irrigation: Yes, for charging plus blocking diode is not required.
Installation: 4pcs 3mm screws
 Connection: solderless;terminals output
Module dimensions:86*63*68(L*W*H)
 Weight: 350g

Pin define:
CV: Output voltage adjustment
Adjust to CV potentiometer, according to your battery or LED to set the required output voltage value.

CC: Output current adjustment
Adjust to CC potentiometer counterclockwise about 30 laps, the output current is set to the minimum,then connect the LED,adjust to CC potentiometer to the required current. (Please adjust the converter after the battery have already been discharged when charging. )Please do not use the short-circuit way to adjust current.

Package Include: 
1 x 1200W 20A DC Converter Boost Step-up Power Supply Module IN 10-60V OUT 12-80V

Environmental Consultants London

Tuesday, 10 May 2016

Bafang BPM Review

Bafang BPM Review - Intro

I you are looking for a large heavy duty hub motor at a relatively low price then look no further then the bafang BPM. At nearly 20cm (8") in diameter it is large. But is is also powerful, with lots of torque.

The Bafang BPM comes in 48v and 36v offering at 350w and 500w power setting, although in reality, these motor can be run at all sorts of wattages and voltages.

In a 20" wheel, the spokes will be short -  110mm approx. 

If you are reading this having noticed that your ready built ebike has a Bafang BPM installed then well done, you worries are effectively over. Spares (yes spares) are available for this motor, including gears and clutch assemblies, so it should last along time. Your main worry would be overheating the motor on a long up hill.

Bafang BPM Review - In Use

In use the most noticeable thing about the BPM is the torque, and how quite it is.

There is a little lag between applying the throttle and starting to go, but the acceleration is rapid, and hill climbing is strong.
Disc Brake Mounts are available.

Bafang BPM Review - RPM Variants

The revs per minute of the motor will ultimately dictate the speed at which you bicycle travels. I have opted for a 230 rpm variant, which with a 20" wheel will give a top speed of approx 14 miles per hour. 15mph is the legal maximum in the UK. So if you are using this motor in a 26" wheel, then you will require a a lower rpm version.

A simple excel sheet can be used to give speed vs rpm.
This RPM vs Speed Spread Sheet can be down loaded here.

Bafang BPM Review - Choosing Voltage

Typically a higher voltage battery pack is more expensive. But if you live in a hilly area it is probably worth it. Here is why . . .

A motors wattage, is obtained by multiplying the volts by the amps it uses, so for example, my 48v motor will use approx 10A of current to produce 500W, a 24 volt motor would have to use 20A of current to produce the same power output.

So if you use lower voltage you will require:
  1. A higher performance battery.
  2. Thicker wires to connect everything up.
Add to this that fact that a motor normally produces far more power than advertised, and you end up with a powerful 24 volt system drawing 30 Amps sometimes.

Bafang BPM Review - Choosing Wattage

Always choose the 500w variant. If you are legally required to use less power then, use a smaller controller. I have read there is no difference between the 350w and 500w versions. I have also read that the 500w version has wider stators (part of the motor). . .  either way the 500w version is normally the same price.

Clearance for mounting brakes etc. is limited.

Bafang BPM Review - Batteries

I have tried to assemble my own battery pack, and wish I have never started. It is not easy. Read my guide on buying a ebike battery. But ignore the last chapter, building a battery is waaaaaaaaay hard.

Again clearance is limited for forks with wide stanchions. 

Bafang BPM Review - Fitting

Forks. Do not use aluminium. There is a guy on youtube who did this, the torque will split the dropout.

The axle on the BPM is a funny size, it is 13 - 14mm on outer edges, but 10mm on the "flats". I presume this is to stop the axle turning in the fork. The BPM comes with torque washers, and various other wasters.

Steel forks are best. But try and choose forks with narrow stanchions. I had to squash by stanchions in a vice to provide clearance for the hub body and disc rotor, which was not very nice.

So chunky BMX forks, are not a good choice, especially if you choose to use disc brakes. 

Bafang BPM Review - Conclusion

There are better hub motors out there than the Bafang BPM (MAC for example), but I do not think it will be beaten on value. 

It offers bags of power.