Saracen / MXUS, 1000w build thread

[averhamdave]

Well the bike runs along quite nicely but I've been disappointed with the speed.

Today I've upped the voltage to 58.8 (14S Lipo) and slightly soldered the shunt.

A short hard ride shows everything to be looking OK. It's now easy(ish) to maintain 24/25mph. It does pull strongly though and the watt meter shows peak watts at 1560.

I'm off into town soon (12 mile round trip) and I'll check the data again when I get back.

 

[averhamdave]

I have to cancel the run into town but have still done 8 miles on the bike just now.

The bike is totally transformed. It is now a 22 - 24mph cruiser rather than 18 -20. I'm cruising on the flat in 7th instead of 6th. There is plenty of punch on the thumb throttle when I need it and it has become a pleasure to rind rather than a slight disappointment.

I think I'll manage by battery power with more miles under my belt (this is my first proper pedelec after 8 years of e-biking). At the moment the stats for the journey are

8 miles
186 w/h = 23 per mile (ie high)
Peak amp draw 27 (was 22 before shunt mod)
3.24 ah used.

The controller is warm - but it is in the battery bag and this is something I'm going to look at. Overall it looks power hungry, which maybe suggests that the MXUS is not actually as good as Bafang's CST.

I think it likely that I will change the lipo storage arrangement soon and put more packs in to give it greater range potential.

 

[Deleted member 4366]

Can you remind me of the spec of the motor. It's 300 rpm, but is it a 36v or 48v? Is the 36v one the same, but 225 rpm?

My Bafang is 36v 270 rpm. With 30 amps and the overdrive set on the 3-speed switch, it pulls strongly to about 21 mph, and then settles to a cruise of 22 to 23 mph with light pedalling. It's about 2mph slower without the overdrive. I'd say at that speed, I'd be using 20wh/m, which compares with yours considering your slightly higher speed, but you need more data to draw a true comparison because wind has a massive affect on consumption.

Apparently the overdrive works by opening extra FETs to reduce resistance somehow. I think it's like running an overlap on the valves with an IC motor, so less efficiency at low speed, although I haven't noticed any difference there. The noise from the motor is different when you engage the overdrive.

 

[averhamdave]

Dave, we were quoted by MXUS as follows, 36v = 240 revs/min and 48v = 300 revs/min

I should be achieving 360 revs/min at 58v.

That should give a theoretical 29mph (yes?)

I am sceptical that the MXUS data was correct.

Anyway my 8 miles today was in very strong winds and you are correct at times the motor was pulling strongly to combat. I'll keep gathering data for interests sake. It won't make the bike go any better but I'd like to see my riding style improve to lengthen pack life and I can measure that over time with the watt meter.

 

[Deleted member 4366]

I looked through your Photobucket but I didn't see any pictures of torque arms?

 

[averhamdave]

I looked through your Photobucket but I didn't see any pictures of torque arms?

There aren't any! It's fitted with AR washers on each side a torqued up pretty heavily.

It was something I have been thinking about. Where's the best/easiest place to obtain them?

 

[averhamdave]

Why has this thread been moved?

If its because its an "over 250w" job, why haven't all the others been moved? There's a long thread still running on the front page which is about the same as this one.

 

[Deleted member 4366]

There aren't any! It's fitted with AR washers on each side a torqued up pretty heavily.

It was something I have been thinking about. Where's the best/easiest place to obtain them?

The BMS battery ones are quite good,or you can get them from Cyclezee. You only need the bit that goes on the axle, and then you can make your own tie-bar to the disc caliper bolt. I've been using the supplied tie-bar, but it's very hard to drill. You need to drill a hole for the caliper bolt and cut off the extra length.
If you zoom in to this one, you can see it

 

[averhamdave]

Thanks Dave, have had a quick look on Cyclezee site and its not obvious where they are. I'll order next time from BMS and just keep a check on the torque until then!

Whilst with this bike, can you, or anyone else discuss a way I can bulk charge the Lipos. (Not looking for a safety lecture BTW). I'd be happy bulk charging and then balance charging every 5th time.

Even my most expensive lipo charger won't put out 60v. If I buy a Lifepo4 charger its charging characteristics won't be right (I don't think). Are they easy to modify?

 

[Deleted member 4366]

Bulk charging is dangerous. Balance charging gives you the chance to check that the individual cells are behaving themselves. If you get a balance board, you can charge all your packs at the same time. You just have the inconvenience of having to remove the series harness each time. Again, before connecting to the balance board, I always check the packs first with cell monitor/cellog/balance meter or whatever. I don't take chances with lipos.

Those hard-packs don't have a good reputation for stability, although most problems show up in the beginning.

If you still want to bulk charge, get one of those BMSBattery chargers. There's a pot in the corner, where you can adjust the voltage to whatever you want, or they'll do it for you.

Alloy Shell 400W LiFePo4/Li-Ion/Lead Acid Battery EBike Charger - BMSBATTERY

Alloy Shell 240W LiFePo4/Li-Ion/Lead Acid Battery EBike Charger - BMSBATTERY

 

[103Alex1]

There aren't any! It's fitted with AR washers on each side a torqued up pretty heavily.

It was something I have been thinking about. Where's the best/easiest place to obtain them?

Have you given the dropouts a check after running several miles without ? With that sort of power .....

 

[averhamdave]

Bulk charging is dangerous. Balance charging gives you the chance to check that the individual cells are behaving themselves. If you get a balance board, you can charge all your packs at the same time. You just have the inconvenience of having to remove the series harness each time. Again, before connecting to the balance board, I always check the packs first with cell monitor/cellog/balance meter or whatever. I don't take chances with lipos.

Those hard-packs don't have a good reputation for stability, although most problems show up in the beginning.

If you still want to bulk charge, get one of those BMSBattery chargers. There's a pot in the corner, where you can adjust the voltage to whatever you want, or they'll do it for you.

Alloy Shell 400W LiFePo4/Li-Ion/Lead Acid Battery EBike Charger - BMSBATTERY

Alloy Shell 240W LiFePo4/Li-Ion/Lead Acid Battery EBike Charger - BMSBATTERY

I already parallel charge as you'll see in the picture below. I can charge at up to 1000w with that set up (input 25v x 40a). I have been using lipos in my RC hobby since they came out so am already very cautious.

Things are now getting messy though because I was running 6 off, 4S packs. Now (because I've gone to 58v) I'm running 4 @ 4S and 2 @ 2S so can't parallel charge the lot in one go.

Changing the set up yesterday to this new configuration has left me with 2 spare, 4S hard packs. What I'll probably do is bring them back into the pack along with another 6S pack to give a 14s3p set up. - Now that will be a rave to charge - hence my thinking about bulk charging.

The discussion has been useful though because as I'm sitting here typing I'm think that whilst all 9 packs are 5000mah, some are 4S and some 6S - so the cells aren't the same are they.

I've no experience at all of bulk charging (other than via a parallel board). Even with this set up, if I set the charger to 57v that would equate to 4.07v per cell which would be safe (I think!!!)

Anyone?

 

[Deleted member 4366]

4S and 6S 5000maH packs are made of 1S 5000maH cells, so all the cells are the same, and only the pack voltage is different.

The BC168 charger charges individual cells. It's like 6 chargers in one, so you can charge 4S, 6s and 2S in your balance board at the same time. Mine worked perfectly for a long time until I left a connector in the board with exposed pins. The pins shorted on some metal. Afterwards, I noticed that two cells on my lipos were about 0.5v down on the others, while as previously they were always perfectly balanced. The charger was mis-reading the voltage on them, so was attempting to over-charge them. Luckily I was suspicious, and checked with another meter. It could have been nasty. You have to set all the channels the same, so I can't use those two anymore. I'll have to put a new one on my Xmas list. They're really useful for balancing any type of battery. You can set any charge rate and voltage.

 

[averhamdave]

Interesting. My understanding , and certainly the case with the Cellpro PL6 and PL8 chargers, is that when balance charging all packs "must be the same voltage and same cell count". It's not something I have had to consider before because I'm usually only ever charging like packs.

Anyway I've loads to do, including making up a new harness and a new battery box!

 

[Deleted member 4366]

The BC168 is different because it has 6 separate channels, and charges through the balance leads, so no series connection. You can have any different number of parallel cells in each channel. Like with any parallel charging, the parallel cells have to be approximately the same voltage before plugging in to the balance board.