How much battery sag is too much for a 3 year old battery?

guerney

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Edit - oh and I was able to disable the throttle in the firmware, by setting it to current control and then setting current at zero. Doesn't work now. I'm fine with that. I don't need it.
I keep a quick release/attach throttle in my mobile toolkit, in case it's suddenly legalised, and for unforseen horrible happenings.


58121
 

Nealh

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Sag at high power /current demand will always be seen , if the battery doesnt't cut out under load then it is ok. Obviously the lower down the voltage one goes then cut outs are to be expected , if under 36v and the battery sags and doesn't cut out then one has to be happy with that as 36v is only approx. 38/40%.
 

Ghost1951

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Sag at high power /current demand will always be seen , if the battery doesnt't cut out under load then it is ok. Obviously the lower down the voltage one goes then cut outs are to be expected , if under 36v and the battery sags and doesn't cut out then one has to be happy with that as 36v is only approx. 38/40%.
Thanks for that Nealth. The question I asked has been thoroughly answered. Nothing to worry about. The range seems less than before, but I never used this amount of power before, and the route at the time in question had covered 25 miles and almost 1900 feet of climbing. Of course the range is less.
 
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Ghost1951

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I keep a quick release/attach throttle in my mobile toolkit, in case it's suddenly legalised, and for unforseen horrible happenings.


View attachment 58121
My throttle is still there, but it is locked out in the settings and not accessible from the screen. I would need to connect the ttl/usb lead and undo the adjustment I made. A throttle that is locked out by firmware, is not a throttle.
 

Ghost1951

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Observations on the battery sag issue:

I've been doing a bit of range testing to try to assess how good the battery is after three years, much of it spent with the bike in the garage.

Now I have adjusted the power parameters operated by the controller by using the serial cable to change values, I have a range of settings that allow:

PAS 1 - max 80 watts
PAS 2 - Max 130 watts
PAS 3 - Max 250 watts
PAS 4 - Max about 400 watts
PAS 5 Max about 500 watts.

So I rode it around , up hill and down dale for 35 miles and the resting voltage dropped from about 41.8 to around 35.6 volts. I tried to put a fair bit of effort into the pedalling myself.

I rode mostly at PAS 2, using more battery power when the hills were getting meaner and some short periods at PAS 5, but only on a long steep climb that I climbed about four times. The height gain was about 300 feet and the length of the climb about a mile.

In the early part of the ride, the motor could easily output 500 watts, but once the battery was down to 36 volts, the pack would only achieve 250 watts in PAS5 on the same hill which had drawn 500 watts at a higher voltage. Of course, fewer volts means fewer watts output, but the current is also falling off as the battery drains. Maybe this is to be expected.

The hill where this was evident is pretty long and steep. If I let the battery recover and rode it on the flat, I could still manage to get about 500 watts out of it. When I returned to sustained climbing, it dropped again to 250 watts max.

To be fair - the battery is perfectly adequate for the rides I am likely to want to do. The hardness of the saddle is still the most likely thing to limit my riding distance.

58395
 

saneagle

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Observations on the battery sag issue:

I've been doing a bit of range testing to try to assess how good the battery is after three years, much of it spent with the bike in the garage.

Now I have adjusted the power parameters operated by the controller by using the serial cable to change values, I have a range of settings that allow:

PAS 1 - max 80 watts
PAS 2 - Max 130 watts
PAS 3 - Max 250 watts
PAS 4 - Max about 400 watts
PAS 5 Max about 500 watts.

So I rode it around , up hill and down dale for 35 miles and the resting voltage dropped from about 41.8 to around 35.6 volts. I tried to put a fair bit of effort into the pedalling myself.

I rode mostly at PAS 2, using more battery power when the hills were getting meaner and some short periods at PAS 5, but only on a long steep climb that I climbed about four times. The height gain was about 300 feet and the length of the climb about a mile.

In the early part of the ride, the motor could easily output 500 watts, but once the battery was down to 36 volts, the pack would only achieve 250 watts in PAS5 on the same hill which had drawn 500 watts at a higher voltage. Of course, fewer volts means fewer watts output, but the current is also falling off as the battery drains. Maybe this is to be expected.

The hill where this was evident is pretty long and steep. If I let the battery recover and rode it on the flat, I could still manage to get about 500 watts out of it. When I returned to sustained climbing, it dropped again to 250 watts max.

To be fair - the battery is perfectly adequate for the rides I am likely to want to do. The hardness of the saddle is still the most likely thing to limit my riding distance.

View attachment 58395
How much current your crank-drive draws from the battery depends more on pedal speed than any controller setting. Any testing you do is pretty well meaningless unless you can match your exact pedal speed up any hill.

There's a chart in post #668 here that shows what you get:

The difference in power between 40v and 36v is 10%, so from 500w down to 450w. To get only 250w, the battery would have to be 20v. Your 250w difference is because you were pedalling faster.

The chart here in post #578 actually shows it better:

Look at the difference. 75 rpm gives 600w and 83 rpm gives only 300w. That's half the power for pedalling 8 rpm faster. This is where hub-motors get an advantage. You can pedal at any speed you want without affecting the current.
 
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Ghost1951

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How much current your crank-drive draws from the battery depends more on pedal speed than any controller setting. Any testing you do is pretty well meaningless unless you can match your exact pedal speed up any hill.

There's a chart in post #668 here that shows what you get:

The difference in power between 40v and 36v is 10%, so from 500w down to 450w. To get only 250w, the battery would have to be 20v. Your 250w difference is because you were pedalling faster.
Thanks for the input. I will go and read that reference you sent me and then i will go right out and try to replicate the issue with a fully charged battery right now. That hill is pretty near where I live. One thing though, and I haven't read #668 yet, is that I went up the same hill and got 500watts when my battery was full.... I'm not sure why I would have been pedalling faster later... but you could well be or probably are right. I am going to test and see.
 

saneagle

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Thanks for the input. I will go and read that reference you sent me and then i will go right out and try to replicate the issue with a fully charged battery right now. That hill is pretty near where I live. One thing though, and I haven't read #668 yet, is that I went up the same hill and got 500watts when my battery was full.... I'm not sure why I would have been pedalling faster later... but you could well be or probably are right. I am going to test and see.
I added more to that post, which might explain. Do some tests with different pedal speeds (gears) and see what you get. It should be interesting.
 
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Ghost1951

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That thread is 'meaty'. I read further than 668, but I am going out on the bike right now since the weather is so perfect. I will come back later and read it thoroughly.

By the way - I was sorry to read about your flu and leg problem. Hope it gets better soon.

I will report later what happens. Since the sensor is cadence based I can try different gears and cadences on the test hill to see what happens. Nothing so scientific as those rolling road traces in that thread will come out of it though - just subjective ramblings...
 

Ghost1951

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I added more to that post, which might explain. Do some tests with different pedal speeds (gears) and see what you get. It should be interesting.
I was ina low gear when the power drop was noticed, but I did alter my cadence and ghost pedal a bit. The more I think about what you and the thread are saying the more obvious it is that the controller was most likely limiting the power. I did think about cadence at the time I was riding though.... This however is not a proper test. Too many random variables at play....
 

guerney

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Look at the difference. 75 rpm gives 600w and 83 rpm gives only 300w. That's half the power for pedalling 8 rpm faster. This is where hub-motors get an advantage. You can pedal at any speed you want without affecting the current.
I can ghost pedal slowly and let the BBS01B do nearly all of the work, then current is limited by my 25A continuous current 19.2Ah battery's capability.


I was ina low gear when the power drop was noticed, but I did alter my cadence and ghost pedal a bit. The more I think about what you and the thread are saying the more obvious it is that the controller was most likely limiting the power. I did think about cadence at the time I was riding though.... This however is not a proper test. Too many random variables at play....
It's your small battery, not enough continuous current. The controller may be set to 100% "Keep current", but your battery can't discharge high enough current continuously.
 
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Ghost1951

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..
I can ghost pedal and let the BBS01B do nearly all of the work, then current is limited by my 25A continuous current 19.2Ah battery's capability.
Right @saneagle now.

Ok. Up at the top of the hill. Battery voltage 39v. I can certainly replicate the cadence cutting power. Pedal like guerney is after me in his orange gimp mask and the power out falls off. When i slow cadence, there is a delay of four seconds and then it surges in again. I would like to maybe lessen that delay, but not sure at this moment which setting to change.

I will need to try and replicate the 35 volt situation to see if the surge will return when i slack off. My memory of the past experiment was that it didn't
 
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Ghost1951

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I still wonder if guerney is onto something about when the battery is nearly done and simply doesnt put out the amps the controller is asking for. Need to drain it and try again.
 

guerney

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Pedal like guerney is after me in his orange gimp mask
How dare you! That's my real face you faceist. ;)

That particular and very practical very old motorcycle jacket style has picked up a whole bunch of undesirable connotations over the years, but it's bloody useful, so it stays.


When i slow cadence, there is a delay of four seconds and then it surges in again. I would like to maybe lessen that delay, but not sure at this moment which setting to change.
I haven't noticed that. You could try that again with Start Degree set to 2?

https://edrivenet.com/bafang-programming/
 
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saneagle

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I still wonder if guerney is onto something about when the battery is nearly done and simply doesnt put out the amps the controller is asking for. Need to drain it and try again.
I can't see that. A battery tries to give all the current allowed and demanded. If it can't supply the current, the voltage sags to cut-off. Only the voltage determines how much power it gives, which is around 10% difference.
 
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guerney

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I can't see that. A battery tries to give all the current allowed and demanded. If it can't supply the current, the voltage sags to cut-off. Only the voltage determines how much power it gives, which is around 10% difference.
Voltage cutoff happens on my bike at 31V, and it's very rare because my battery is large enough to cope with many long zero effort hill climbs.


58396



I still wonder if guerney is onto something about when the battery is nearly done and simply doesnt put out the amps the controller is asking for. Need to drain it and try again.
Whatever state your battery is in after three years, if you're surrounded by many hills, your battery was too small to start with.
 

Ghost1951

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Whatever state your battery is in after three years, if you're surrounded by many hills, your battery was too small to start with.
This might give you an idea of the terrain. That drop off into the valley is about 500 feet of vertical or more.

This is my old retired 125 that I bought when I came here and struggled to pedal up these monster trails. There is nowt wrong with that bike mind you. I just have two better ones now so it is resting in the garage.

58400
 
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Ghost1951

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I can't see that. A battery tries to give all the current allowed and demanded. If it can't supply the current, the voltage sags to cut-off. Only the voltage determines how much power it gives, which is around 10% difference.
That makes sense. The voltage did not collapse during the episodes in question. It just sagged a bit to about 34 /33. I was in the lowest gear to enable me to assist substantially, so I may have been spinning a bit. The delay in the motor kicking in (about 4 seconds) after a pedalling change may have covered up my slower cadence tests so I thought no change was happening.

Anyway - I could certainly see how rapid pedalling this morning cut power from 500 to about 250. It was quite a high cadence mind, but it definitely happened.
 

guerney

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This might give you an idea of the terrain. That drop off into the valley is about 500 feet of vertical or more.

This is my old retired 125 that I bought when I came here and struggled to pedal up these monster trails. There is nowt wrong with that bike mind you. I just have two better ones now so it is resting in the garage.

View attachment 58400
It can be a 709ft climb (or more, depending on the route) back up in total to get home, after I pretend to cycle 15 miles out, with lots of hills and dales in between, sometimes while dragging a heavy bicycle trailer. I don't think a 13Ah battery would cut it, even for my smaller wheeled bike. Certainly not for my longer journeys, and not with my easy to pedal high power usage setup.
 
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Ghost1951

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I added more to that post, which might explain. Do some tests with different pedal speeds (gears) and see what you get. It should be interesting.
I can't see that. A battery tries to give all the current allowed and demanded. If it can't supply the current, the voltage sags to cut-off. Only the voltage determines how much power it gives, which is around 10% difference.
You were right saneagle.

I took it up there again this afternoon after 28 miles since charging and this being the fifth hard climb up the hill. The battery resting voltage is now about 35 volts and when I go up the steepest part of the hill at the highest assistance level, the voltage sags to 32v, but it still puts out about 500 watts as long as my cadence doesn't go up too high.

My previous query arose because I was in a very low gear and pedalling like the devil to help it up and retain at least some self respect as a one time proper cyclist.