Overamping and/or overvolting 9c clone hub

[Haien]

I recently built an ebike from one of those cheap kits on amazon, and it is really fun, though quickly felt lacking in both speed and acceleration.

Apart from the controller already connected I have got another one rated for 48 to 72V and 50A, though the capacitors inside it were 100V ones. My battery is a downtube 52v 14s5p 40A BMS by Unit Pack Power. Would it work (and give me better torque) if I simply swapped controller to this higher amperage one, or would I risk blowing the BMS or batteries? Is trimming the shunts the only way of slightly lowering the amperage draw on these cheap controllers?

As this controller is rated up to 72V, and the known cheap and dirty way of getting to 40 mph is feeding these 9c clones with 72V 40A, could I connect a booster battery of about 20-24V in series with the 14s5p whenever I want to try that? Would two SLA 12V 12Ah in series work if I carefully monitor the voltage and don't let them drop below 11.80V each (empty voltage). If I use Andreson conncetors I would be able to connect the booster when I want it and disconnect it when I don't or it goes out of power. Or would it be better to use a few 20V cordless drill batteries in parallel? I would prefer this, but I already have those two 12Ah SLA:s, and I would still need to check voltage as it would be hard to get 17.5Ah.

Thanks in advance!

 

[Nealh]

Your 40a battery wil be shagged by the 50a max current of the controller. To use that controller you will need a battery capable of 60a current draw or more using top 20a cells from LG or Sony.
I should think your battery will have 10a cells but we would need to know the exact cell used as cell specs all vary.
The 50a controller will try and draw more then the 40a rated battery can supply, you will get no more then 3 months use out of it if max current is drawn. If anything the cells will over heat and be damaged well before 3 months , the BMS although 40a rated will allow over current for short periods. Ultimately the risk is the pack could smoulder or go up in flames.

Forget SLA for high current draw under continuous use they are not designed for this type of use, Li batteries are your only option. SLA don't have the voltage discharge characteristics of Li, their main use is for instant high current for turning motors over not for drawing continuous high current.

 

[vfr400]

Show us a picture of your bike.

 

[Haien]

Your 40a battery wil be shagged by the 50a max current of the controller. To use that controller you will need a battery capable of 60a current draw or more using top 20a cells from LG or Sony.
I should think your battery will have 10a cells but we would need to know the exact cell used as cell specs all vary.
The 50a controller will try and draw more then the 40a rated battery can supply, you will get no more then 3 months use out of it if max current is drawn. If anything the cells will over heat and be damaged well before 3 months , the BMS although 40a rated will allow over current for short periods. Ultimately the risk is the pack could smoulder or go up in flames.

Forget SLA for high current draw under continuous use they are not designed for this type of use, Li batteries are your only option. SLA don't have the voltage discharge characteristics of Li, their main use is for instant high current for turning motors over not for drawing continuous high current.

That is what I though may be the case. If I make sure to not constantly draw that much and only do on occasion then? I think I'm going to buy an ammeter and voltmeter to constantly monitor these things. While cruising at 20 to maybe 30 mph (30-50kmh) it surely won't draw more than 25-30A on the flat, as I can get 30mph now on the stock 1000w controller. If that is also too risky, wouldn't trimming the shunt(s) in the controller lower the amps (doing the reverse of a normal shunt mod)? Lowering max amps to 40 should surely be safe if I still mostly cruise low speed and just go full throttle on occasion.

The sale page of my battery just states Samsung 3500, which seems likely to be true looking at the 17.5Ah and 5P spec. If they used these batteries drawing 50A would be a problem.

I wouldn't use the SLA boosted configuration for anything more than a few minutes at a time. This would be more of an experiment than anything else, if I like it I may get some lithium 5P to get the voltage where I want it. I know for sure SLA can be used continuously, but compromised compared to lithium, as some use it for ebikes and I have had a chinese scooter that used those before. As said, this would only be a experiment, I am just worried it will damage my lithium battery or its BMS if connected in series.

 

[Haien]

Show us a picture of your bike.

I think I'm going to get a rack on which I will mount my bigger controller and get rid of the hanging bag. Will make the wiring a bit neater too then, maybe add a switch for the speed limiting wire.

 

[Haien]

Your 40a battery wil be shagged by the 50a max current of the controller. To use that controller you will need a battery capable of 60a current draw or more using top 20a cells from LG or Sony.
I should think your battery will have 10a cells but we would need to know the exact cell used as cell specs all vary.
The 50a controller will try and draw more then the 40a rated battery can supply, you will get no more then 3 months use out of it if max current is drawn. If anything the cells will over heat and be damaged well before 3 months , the BMS although 40a rated will allow over current for short periods. Ultimately the risk is the pack could smoulder or go up in flames.

Forget SLA for high current draw under continuous use they are not designed for this type of use, Li batteries are your only option. SLA don't have the voltage discharge characteristics of Li, their main use is for instant high current for turning motors over not for drawing continuous high current.

I checked my SLA batteries again and they were apparently 14Ah. I found a chart listing max current draw for SLA under 7 and 30 minutes. 42A is not too bad keeping in mind that's what my lithium cells will safely output.

I may look in to that shunt mod, or just opt with the ammeter and maybe add a fuse at 45 or 50A.

 

[vfr400]

A 33A or maybe 35A controller is about as high as you can go with that battery because of the BMS.

Your cells are rated at 8A max. You should aim not to go over 50% of that for continuous current when designing your system. For 5P, that would be 20 amps, so you're already stressing your battery. I bet it already gets warm when you do a high power run.

Another thing that people don't realise is that you have 4 times the energy when you double your speed. Your brakes are just about OK for 20 mph riding. For 40 mph, you'd need 4 of those brakes on each wheel to dissipate your energy in the same way your present brakes can. That's if your tyres can gain the traction needed. The knobbly tyre you have on the front has no chance, and the one on the back doesn't look up to much either.

 

[Haien]

A 33A or maybe 35A controller is about as high as you can go with that battery because of the BMS.

Your cells are rated at 8A max. You should aim not to go over 50% of that for continuous current when designing your system. For 5P, that would be 20 amps, so you're already stressing your battery. I bet it already gets warm when you do a high power run.

Another thing that people don't realise is that you have 4 times the energy when you double your speed. Your brakes are just about OK for 20 mph riding. For 40 mph, you'd need 4 of those brakes on each wheel to dissipate your energy in the same way your present brakes can. That's if your tyres can gain the traction needed. The knobbly tyre you have on the front has no chance, and the one on the back doesn't look up to much either.

Thanks for your input.

I won't be using more than 20 or maybe 25A when cruising (slow) or accelerating slowly, it will just be when doing a hard acceleration I will be exceeding 35A, but I get that it wouldn't be a good idea to try drawing more than 40A. Though, would allowing bursts of 40A be that bad? It is after all what Samsung has rated them at.

A few days ago I rode for at least an hour pretty hard testing my new ebike, and the battery got almost lukewarm to the touch (mind you my hands were cold as I didn't wear gloves), I'd say it got to room temperature or slightly above.

I totally get that energy isn't linearly correlated to speed (Ek=(mv^2)/2), but I also try to ride responsibly. Going 40mph with the SLA:s would only be an occasional thing. 30mph is almost too fast to be comfortable for commuting. My hydrualic disc brakes are also probably as good at 30mph as caliper brakes are at 20mph.

 

[Nealh]

The Samsung 3500 cell is the 35E which has a max 8a draw, it isn't a high current cell.
You need a better celled battery for 35a current draw.

 

[Haien]

The Samsung 3500 cell is the 35E which has a max 8a draw, it isn't a high current cell.
You need a better celled battery for 35a current draw.

Wouldn't 35-40A peak work? Again, continually I won't use more than 25A.

 

[mike killay]

Thanks for your input.
My hydrualic disc brakes are also probably as good at 30mph as caliper brakes are at 20mph.

I think the main problem with your disc brakes is the thin, flimsy nature of discs intended only for cycle use. They will soon overheat and warp.

 

[Nealh]

Wouldn't 35-40A peak work? Again, continually I won't use more than 25A.

35/40a peak is for 5 or 10 seconds only then damage will occur, one will only know if 25a is drawn by having a ammeter wired in and visible.
Nearly everyone would use a battery capable and in excess of what the controller can demand to play safe, going about it ass about face is asking for trouble.
Be safe limit your battery to a 25/30a controller.

Look on utube for bikes going up in flames where riders operate bikes outside of the window,

 

[vfr400]

I get that it wouldn't be a good idea to try drawing more than 40A. Though, would allowing bursts of 40A be that bad? It is after all what Samsung has rated them at.

What you're not getting is that your BMS will cut off at 40A.

My hydrualic disc brakes are also probably as good at 30mph as caliper brakes are at 20mph.

Caliper brakes are good for 12 mph. Hydraulic disc brakes are good for 20 mph. For 30 mph, you need top spec hydraulic brakes, like Hope double piston and decent rotors. See the problems that Soundwave had with standard brakes when he derestricted his bike, and his bike weighs a lot less than yours. If he reads this, I'm sure he'll show you.

 

[Haien]

What you're not getting is that your BMS will cut off at 40A.


Caliper brakes are good for 12 mph. Hydraulic disc brakes are good for 20 mph. For 30 mph, you need top spec hydraulic brakes, like Hope double piston and decent rotors. See the problems that Soundwave had with standard brakes when he derestricted his bike, and his bike weighs a lot less than yours. If he reads this, I'm sure he'll show you.

From what I have read, the BMS rating is max for constant discharge, peaks of a couple of seconds higher will not get it to shut of. It says "Maximum constant discharge current: 40A" on the product page. I won't draw more than 40A, but I may want to draw just 40 or slightly below it.

I didn't say my brakes were a good idea at 30mph, I just said they are probably as good at 30 as caliper ones are at 20.

 

[Haien]

one will only know if 25a is drawn by having a ammeter wired in and visible

That is what I plan on having

 

[vfr400]

From what I have read, the BMS rating is max for constant discharge, peaks of a couple of seconds higher will not get it to shut of. It says "Maximum constant discharge current: 40A" on the product page. I won't draw more than 40A, but I may want to draw just 40 or slightly below it.

I didn't say my brakes were a good idea at 30mph, I just said they are probably as good at 30 as caliper ones are at 20.

Well, if you know better, go ahead.

 

[Haien]

Well, if you know better, go ahead.

I don't, that is just what others have said and what I have read on other sites. So the BMS will shut the power supply of if current goes over 40A? I will not draw that much then. But if the cells are rated at 8A each, wouldn't it be safe to draw that much? I feel like the limit would be lower if it was dangerous to draw 8A from that cell, or don't I get the ratings?

 

[Haien]

I will not draw more than 40 amps from the battery as that is dumb, but I still want my 50A during acceleration. I have an idea. What if I connect a super capacitor bank in parallel with the lithium battery? The Amperage will be shared between the two allowing well beyond 50A total being drawn. I will install an ammeter for total draw and one for just the lithium pack along with a 35A fuse for it. Depending on the size of the supercaps I should get a few seconds of full amperage, just enough to get up to some speed and not needing the same amperage.

What do you think, has anyone done this before?

 

[mike killay]

I will not draw more than 40 amps from the battery as that is dumb, but I still want my 50A during acceleration. I have an idea. What if I connect a super capacitor bank in parallel with the lithium battery? The Amperage will be shared between the two allowing well beyond 50A total being drawn. I will install an ammeter for total draw and one for just the lithium pack along with a 35A fuse for it. Depending on the size of the supercaps I should get a few seconds of full amperage, just enough to get up to some speed and not needing the same amperage.

What do you think, has anyone done this before?

Probably not.
Tell you what, go ahead and let us know what happens.

 

[Haien]

Probably not.
Tell you what, go ahead and let us know what happens.

I figured it would require so complex electronics it would be worth just buying a bigger battery.