New ebike build problem

Hi all
I have just built my second ebike - the first being a cheap voilamart 1000w 48v kit which I did over 1000 trouble free miles.
Now I have just bought a 72v 3000w kit off eBay - second hand but brand new (guy realised price of battery and didn't bother going any further).
Anyhow.. my battery finally arrived today (electron 72v 20ah hard case triangle battery).
Hooked it up this morning ... Quite a spark upon connection but still showing just under 80v at the terminals.
However the sw900 display just won't turn on.
Yet if I disconnedt the battery I can get the display to turn on for a few moments until the capacitors drain.
What gives ?
The controller is a generic brushlsss motor jobbie with the following spec
48/72v
60 amp

Could it be it's configured to 48v in the display and it's cutting out due to over voltage ?

Thanks in advance for any ideas
Jonathan

Quick update
Turns on normally with a 24v power supply
Hold down the M button and it powers up
BUT on the 72v battery
I need to quickly double click the M button and then hold
Then it turns on...
What gives ?
Anyone had something similar ?

Its hard to comment when you do not tell us the make or model of the display
Suggest you Email/contact the manufacturer for information ?

Hi,
As mentioned in the first post it's on of those ubiquitous sw900 displays with the three button handle bar mounted mode switches (arrow up / mode / arrow down)
On anything less than 72v you simply gold the middle mode button 3 seconds to turn on the display / bike.
When on 72v I have to tap the mode button 3 or 4 times then gold the mode button to turn the screen on.
Simply holding the mode button for 3 seconds on 72v does nothing .
Its an odd issue for sure.

Jonathan

Do you have the display operating manual ?
https://www.fatbikeshop.fi/wp-content/uploads/2018/08/display-SW900.pdf
It suggests 24/36/48v are the factory options....but other voltages are possible ?
Suggest you contact one of those suppliers as to how to reconfigure for 72v

i know this can't help u but i was wondering how did that vpilamart 1000w build go
i planing on building the same one where did u p/u the kit from thanks

Hi Hillhater,
The controller is rated 72v and I also configured the SW900 to 72v also (it had options for 24v 36v 48v 60v 72v).
It did not make any difference regarding this setting - I actually assume that only affects the battery level indicator - as it also changes the cut off/ warning voltage.
Anyhow - it is working consistently by tapping the mode button 3 or 4 times then holding - its just such an odd issue - had I not figured it out, I would have been completely stuck.
Regards,
Jonathan.

Hi Indian Scout......
I purchased the voilamart kit from ebay about 1 year ago for £130.
It was simple to fit with no issues - i hooked it up to a hailong downtube battery 48v 13ah (again ebay around £220).
This seemed about right for my needs.
I could go 70km at a constant 30kmh with some pedaling OR 20km with zero pedaling riding hard
top speed was a reliable 50 kmh
used in all weathers - no issues whatsoever
I ended up modifying the controller (adding solder to the 2 shunts) to up the power from 1000w to around 1700w
this does NOT affect top speed (that is voltage) but it had a lot more pull - not that it really needed it - I just like tinkering
I sold it to a friend and its still going strong
I never bothered fitting the PAS - used throttle only
and I tidied up the cabling by removing unused wires - like the brake switches and pas unit
so - regarding my build at least - I would recommend
Jonathan

to give some comparison with the 1000w kit
I have only ran the new 3000w kit for a day or two
top speed is around 88kmh - which is more than plenty on a standard mountain bike I can tell you.
So far I have done 48km without turning a pedal and still have around 60% battery left
battery pack is 20s5p samsung 40t cell 20ah triangle pack from electron cycles with bluetooth bms - 125A (200 max)
controller is 60A (so the battery is not a bottle neck)
it accelerates quite hard up to about 70 plus kmh then it starts to ease off a bit until top speed is reached
everything is running nice and cool

j brown i want to thank u for your reply
this is my first time doing this
im going to try to build myself one
wish me luck

Testing complete
Works well (other than the power on issue)
I used an old inner tube to route all of the cables an connectors into with tie wraps at either end

Worked well tbh