Revisiting the Battery Load Draw conundrum for bicycle charging as based on Ohm Resistance: The Back-EMF limit for the minimal load draw

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Ben Central 9 months ago

This is true voltage is not the actual thing flowing but rather a "pushing force" Amperage is the a measurment of the current flowing through the wire

Voidisyinyang Voidisyinyang 2 months ago

@Ben Central yes they are incorrectly claiming high amps when in fact the battery resistance is very high since they are just topping off their battery.

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Nikola Yordanov 6 hours ago

You can't monitor output amps. There has to be a load, and you can see how much amps the load draws, and how much it drops the voltage

Voidisyinyang Voidisyinyang 2 hours ago

@Nikola Yordanov yes unfortunately the resistance of batteries are typically too low so the draw is not strong enough. But they have their batteries with loads on them and then they are just topping off their batteries under load. Normally a battery charger for any kind of inverter has a built in voltage management at around 80%. So the draw as resistance is increased dramatically to then drop the voltage level to make sure the battery is not over charged. So then if you are trying to charge when the battery is being topped off - then it will take an extra long time to do the last 20%. 

For lithium batteries there is even a final 1 hour for just evening out the individual cell voltages without any amps going in at all. So yeah unless we know what kind of loads they have then we can't know the amps - you are correct. I have uploaded on my channel different draw load examples - so I pedal at 6 amps for light bulbs - 12 volts - oh that must have been 5 amps so 60 watt light bulb at 12 volts. But since the load was so strong then the resistance was - what's Ohms again? volts/amps I think - so over 2 ohms - resistance on PEDALING was also very strong. So it's better to do low watts for a longer time and then power a device directly without charging a battery. I power a 10 watt DVD player so then I can watch a whole movie without being worn out.  

Right now I have a battery of 31 amp-hours - I have used it down to about 20 percent. So it's only at 6 amp-hours. I also have a DIGITAL DC-DC buck converter so I can read digital amp output of my DC motor generator-bicycle charger. So I'll try charging up the battery on bicycle and see how many amps the generator draws. But I think the internal battery management system will limit the amp draw to just 6 amps at most. Normally I just get a 3 amp draw on the generator-battery-inverter and so that does not create too much pedaling resistance. So that way I can pedal for an hour and increase the generator charge by 10%.  

Oh I remember now - I had a 10 watt draw hooked up to the DC output - but it kept shutting down because the cord had the polarity switched. So... yeah I was gonna check how much draw I could increase by having the battery load increased while charging. It depends on how the cells of the batteries are hooked up. I have 9 cells for 4 packs each for 36 total cells for 346 watt-hours. So they are wired in parallel so the draw is actually just for one of the four packs of 9 cells. 31/4=about 9 amps per cell. So at 12 volts the Ohms resistance is 1.3. The built in battery management has I think an 8 amp fuse or something - so I think it will only draw at that limit. Yeah so a normal 12 volt battery I suppose has no limit - just the total amp hours will give the ohm resistance based on how close you are to topping it off. Oh my car charging was not working - I'll test that first. That normally draws only 6 amps.

Voidisyinyang Voidisyinyang 2 hours ago (edited)

@Nikola Yordanov OK so I just drove 2 miles. 1 mile I had the generator charging with the battery management system turned ON - and the charge went up only 1.5% in a mile. Then turning around I turned OFF the battery management system and after a mile when I switched it back on I was up to 28%. So that was double since it was a 3% increase in a mile. So that means I was drawing maybe the full 12 amp output on the cigarette lighter into the 31 amphour battery!! 

So now I'll try the same with the bicycle generator - with the battery management system on and off - to see the amp draw difference. Yeah I guess the fuses are higher than I thought since I didn't blow any fuses on the generator. I have the data on my blog... "so I'm getting an 80 watt inverter - to convert my car's 15 amp output back into 5 amps." Oh - I forgot that is what limits my amp output - the plug inverter! OK - so that means the draw was around 5 amps without the battery management system on - but that was the limit of the inverter. 

So WITH the battery management system on - the draw was lower... back down to 3 amps again (even though the car puts out 15 amps!). "built-in 36 pieces, 3.7 V, 26000 mAh 18650 lithium battery, so the theoretically capacity is 36 * 3.7*2.6 =346.32" So that's my battery stats as I blogged: https://elixirfield.blogspot.com/2019/01/reverse-engineering-chafon-500-watt.html O.K. so now we know why typically you want a 5 amp limitation on charging, to spread the 12 volt down to 2.7 amps. So a cell of 4 = 10.8 amp limit on charging. Yep it has a 10 amp protection circuit module.  

"CHARGER CURRENT REQUIRED = 26.4 AMPS + 2 AMPS = 28.4 AMPS. 8. Choose the next biggest charger in the range e.g. 12 VOLT, 30 AMP, 3 BATTERY BANKS = BCM 12/30-3" I had no idea you could charge 12 volt batteries at such high amps!! So I guess it's not based on each cell amp level of the battery. But that's different than the draw load of the battery since a bicycle generator is pushing the energy only based on the draw - as you emphasize. So the resistance of the battery should be based on each cell. That link states the typical 12 volt is wired in series of 2 volt cells. OK so that's why the amps are not limited. Whereas my battery is wired in 4 cells in parallel.

Voidisyinyang Voidisyinyang 1 hour ago

@Nikola Yordanov I reset the Dc-Dc buck converter to over 8 amps to see if the battery would draw that much but I forgot to SAVE the settings. I have to review the instructions. I had it set to limit to 1.5 amps for powering the portable DVD player (10 watts)....

Voidisyinyang Voidisyinyang 28 minutes ago

@Nikola Yordanov OK NOW I remember the issue - they're getting BACK-reaction or reverse torque from the EM-field reversing. I just got over 4 amps charging into the battery. But the bicycle I'm using now is a smaller frame - so I couldn't pedal at fast enough volts (rpms) to overcome the back field of the reverse torque. I did a blog post on this. https://elixirfield.blogspot.com/2019/02/eb-aka-back-emf-aka-counter.html Yeah so that's the real cause of their high resistance. They can't get over 4 amps I'm sure - since they have a similar treadmill motor as I do. 

 https://elixirfield.blogspot.com/2019/02/eb-aka-back-emf-aka-counter.html So a battery doesn't have a DRAW since it's not a motor. That's why the back reaction is so strong - it's similar to pedaling into a multimeter. "Applying a load (torque) to the output shaft slows the rotation speed and reduces the back emf. This in turn will increase the motor current." So if I increase my voltage on my DC-DC buck converter then I should be able to decrease the Back EMF but since the total amps is only 10 amps - that means the load of the battery is probably too low, therefore the Back EMF is too strong to go higher than 4 amps pedaling. At any rate 5 amps can not be sustained for very long. So my guess is these guys are doing 3 amps at most.

Nikola Yordanov 28 minutes ago

@Voidisyinyang Voidisyinyang ye.

Voidisyinyang Voidisyinyang 2 seconds ago

@Nikola Yordanov Sure enough it worked (using the new digital DC-DC buck converter). I increased to 13.8 volts charging output and I got up to 5 amps charge output from the bicycle! But I couldn't hold it since this bicycle frame is smaller so my legs are too long (the bicycle seat is not the proper one so I can't adjust it). haha. Even still it was way too much work. Anyway proved my point in concept.

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So the resistance of the Lithium battery is much higher since it's split into 9 packs of 4 cells. So then 14.8 volts / 10.4 amps per pack of 4 cells = OHMs of 1.42

Whereas a standard 12 volt battery has no parallel wiring so it's just total volts of 12 total amps. So then the resistance is very low since it's - oh wait that's for 3 batteries? So it's only a 10 amphour battery. So it's 1.2 Ohm. Pretty similar!