top speed is down on my BD36

[needWheels]

It's strange that now I only get a 21.8 mph max stop speed.
Aren't BD36 supposed to have 25mph max on flat ground with SLA?
Are they stating that with 36v or the SLA full charge of 40.8v+ ?

There was an earlier BD36 version that had a 20mph top end but
I believe this one is from late 2006 and is a 25mph model.

I just tested it with two speedometers (got a second one after I thought I broke my first).
I'm using 26x1.5" tires and a speedometer of 2030 which is manufacture suggestion for that size.

Went a half mile out and back on flat ground. No wind I could detect.

I suspect I have weak batteries. In fact the starting voltage is 40.3v
Voltage after I came back was 38.8v Is that okay for 1 mile? They are just 7ah SLA.
So SLA is supposed to have 13.6-13.8 standing voltage right?
That means I'm only starting at 13.4v per battery.

I'm using 14 guage wire to connect the batteries, that's not holding me back is it?

 

[dogman dan]

If the wires get hot it's holding you back. Have you discharged the batteries all the way to the bottom lately? And lastly it could be weather. When I ride home in 100f my motor gets a lot weaker after it gets all hot. I'm having a similar problem with mine, but i think it may be a broken connection inside the duct tape. Yesterday my battery went empty about 15 miles sooner than normal.

 

[Drunkskunk]

what apmerage are you running this at? if its 15 amps, then the batterys are running at more than 2c. That will kill SLA fast. and 15 amps might not be enough to hit 25. it might take 20 or more. at 20 amps, you're at 3C. the voltage sag at 3C might keep you from ever hitting 25.

Also, how heavy are you?
whats the pressure in your tires?
what tread pattern?
what riding posture do you use?
do you wear normal cloths, or riding suits?
how well do you heep your hubs and chain oiled?

And most importantly, have you ever had this bike up to 25?

 

[needWheels]

It may very well be the amp limit. I did not know how many are used @ 25mph.

These are only 7ah SLA's (RBC2) and might not have enough current available, they are not in great shape.

The fastest i have been is 27.5mph with 48v - and that was likely on a downhill.

I'll try rigging 36v x 2 (parallel) and see if that changes the top end at all.

The tires are 26x1.5 @ 60psi and are nashbar urban's:
(only the center ridge touches the ground when you are vertical, it's a recessed tread)

 

[D-Man]

A voltmeter on board while riding would help you diagnose if batterys are ok.

 

[Link]

I doubt it's the sag on the batteries, though if they are really old, I dunno. I was running 4.5A SLAs on a 30A controller and could hold 27mph with the 48V/26" setup until they were near dead.

~800W (48V x 20A) seems too high for only 25mph, even when factoring in the motor's inefficiencies. I can do that on a regular pedal bike, and I'm quite sure I'm not reaching that kind of power output. I'd check the 'Zotter for a better estimate, but it seems to be down again. :?

 

[dogman dan]

My bike is back to normal now. Just needed a better charge on the ping. dunno why it was weak for 2 charges, but its ok now. Looked inside finally and liked what I saw. Lots of beefy solder that looks good connecting the pack tabs and no weak cells. Bms wires could still break, which is what I thought was wrong. Is your bike consistently slow, or just one time? Maybe your charger just shut off early for some reason.

 

[needWheels]

For the last few rides, max is 21.8-21.9

I highly suspect the batteries.
25mph may just be when the batteries are fully topped to 13.8v = 41.4v

mine START at 39.3 or so lately, and that's fully charged to green

Eh I've been doing 24v for now anyway, it encourages me to pedal more.
I didn't think the controller would even let me run at 24v but it does.
Been thinking of just getting a 24v LiFePo4 instead to save.
Supposedly the YESA's BMS can be put in serial or parallel so 2 24v YESA would give me options.

 

[dogman dan]

Though my bike is back to normal, I find 20 mph more and more comfy than 25, just because I can peadle, and the bike feels right to me then. When i ride the bike with sla's I don't get 25 mph for very long, and then it settles in at about 20 mph for most of the ride. I think 40 volts about = 20 mph. If your ride is short, don't worry about it too much. If you do want to go to 24 v, two 12ah slas is pretty cheap and weighs 20 pounds. Pretty tolearable if it is in your range.

 

[needWheels]

Top speed is now 19.2, can't even do 20mph on level ground with no wind.
So the batteries must definitely be dying. Sigh, was hoping to get a bit more time out of them.