Introduction: EBike Conversion on a Budget

Simple eBike conversion
Bike $65 at opshop - would recommend disc brakes as you are going faster

Kit $220 when purchased (prices have risen since)

Step 1:

Batteries where from 2yo medical equipment battery packs and measured >2Ah/cell - got them for free
Configured in 13s8p configuration (769Wh) - photo shows 12s8p but added another set soon after.

With a 1000w motor at 48v max current would be 20.8amps

Each battery would have a 2.6amp load - well within spec of most cells

Used a 25A cct breaker as a battery disconnect (cost <$5)

Step 2:

Charger is a boost converter set to 13x4.2v = 54.6volts
Added a 5A diode to the boost converter output for reverse power blocking (need to add 0.6v to 54.6volts) Did not use a BMS but can monitor pack when charging as there is connector that all battery set voltages measured

Controller has a low voltage cutout so it will protect cells. If it cuts out you can still use power at a lower throttle.

Has been working for a year with no real issues

Suggestion is to remove the bullet connections on the motor wire as these melted - use a terminal block

Step 3:

You can use a laptop power pack for the boost converter - most can do over 120w these days

For me the boost converter is powered from a 24v SLA battery pack (milk crate with 16x 7Ah batteries - 1344Wh - enough for almost 2x charges) charged by a 30v 200w solar panel using a 25amp diode bridge to drop the voltage by 1.2v (30-1.2=28.8) close enough for float voltage

(photo shows setup for my 36v bike and 18v battery pack charger)

Cost - batteries were $0 cost as they were swapped out every 2years - could using 2 similar capacity car batteries.

Solar panel was $40 - they are even cheaper now that so many houses are upgrading solar installs

25A bridge rectifier - $5

Setup has been working for many months

Step 4: Adding Car Horn, Lights and USB Power

After riding bike for a while it became evident to have a louder warning device

Used an old car horn - these take a lot of power so used 3x 18650s (left over from the main pack assembly) in series for approx 12V (can use lipos too). Used a microswitch for car horn as I had at hand and they have decent contact rating.

This battery pack can be recharged from main battery (after the switch) via a high voltage buck converter set at approx 12.6volts/ 1 amp.

Added lights - front light is 12V 5W MR16 as it was handy and cheap. Rear light can be RED 12V led strip or 12V red led (5x high brightness red leds in series with a 50-100ohm resistor)

Will also add 5V USB converter - Can use any 12V cigarette lighter type

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