Battery power dependent on level of charge?

[6zfshdb]

Wouldnt it be better to just put more P in to reduce sag.
Lot of factors mainly how much you are pulling.

It isn't so much the voltage sag, but rather the loss of motor current as the voltage drops (wattage) that affects performance. As long as the battery voltage is higher than the motor rating, in theory, the buck converter will maintain both voltage and current at a constant level.

For example, a 52V battery cuts out at around 42V, which is higher than a 36V motor rating. In theory, a buck converter should be able to maintain constant voltage and current until the battery LVC cuts out.

As you say, there are many factors involved and it's difficult to know how the controllers on e-bikes would react. Hopefully, I'll get around to doing some experiments in the near future.

With a little design modification, e-bike controllers could do this internally. I know the controllers on some bikes already do, but unfortunately, most don't.

 

[Gionnirocket]

Exactly... I'd rather have a larger battery (more cells in parallel) that will also extend range than adding hardware to combat sag.
Also keep in mind having a lower voltage motor introduces other inefficiencies.

Personally I don't find sag that big of an issue...
YVMV

 

[Mr. Coffee]

...
But.....Im asking for help here...volts is speed, current is sort of torque? but it needs volts for more power.

Extremely sort of.

This is all extremely approximate but I'll try to give a simplified explanation:

Imagine if you take an electric motor and feed a constant voltage. The motor will spin at a certain speed (RPM) for that voltage. Increase the voltage and you'll get more RPMS. You haven't connected the electric motor to anything yet so it draws very little current.

Now imagine you have a wheel attached to the motor and the wheel is spinning in the air at the same RPMS but the motor is now drawing a bit more current.

Put that motor and wheel on a bike and put 100kg of rider meat on the bike and on a level, smooth roadway the wheel still spins at that constant speed but the motor is now drawing even more current.

If that whole system now goes up a steep, rough hill the wheel still turns at the same speed (given constant voltage, again) but the motor is drawing even more current. You can keep increasing the amount of work the system is doing until the motor burns out. Then you can't do any work.

And "work" is the literal technical term here. Under Newton's laws work is force times distance. You need more force to move more stuff a given distance in a given amount of time. If you want to move stuff faster you need more power, because you are doing more work in a given unit of time.

 

[PCeBiker]

I use both. That way, I get the benefit of analog + digital:

I've got the same type of digital gage that I never installed,..

I don't like the how display only shows one thing at a time, and all the screens kinda look the same with the decimal point, V, A, and %, being hard to see.


And,.. I don't want to know how much battery I've got left, I wanna know how much I've used.
I have a 19ah, 21ah, and a 25ah battery, so I'd have to reprogram it whenever I swap batteries to at least get the bar graph working properly. I'm not sure how the total Watt Hours are displayed?

And then to top it off, I bought the wrong one with a 500 amp shunt.

That'd be like trying to use a bathroom scale to weigh dime bags.


So I ended up buying this,..

I ordered the gage that comes with 50 amp shunt, but they sent me the 100 amp shunt.
The version that only reads up to 20 amps, has a built-in shunt, but that would mean that I'd be running Full battery power from the battery to the handlebars somewhere, then back down to the battery wire splice, and I don't want all that power going to the handlebars.

I've got a 20 amp shunt that I might be able to use, but my ebike display says the controller draws up to 21 amps, and I don't know what the gage will do if it receives more than 75 mV?
It should only see (21÷20×75) 78.75 mV which shouldn't blow anything up, but it might piss off the programming or something? And my e-bikes' power/current displays are dummy gages too with all that logarithmic, AI BS tampering with the readings, so who knows how much current is actually being drawn from the battery?
(I don't care what the motor is using, I'm not going to burn it up. I want to know how much the battery has put out.)

So I bought a new 50amp shunt that cost twice as much as my 20amp shunt thinking that it might be better quality and more accurate.

It might be reading almost half of full scale, so it should be pretty accurate?
I can buy a 30amp shunt which would be perfect, but I can't set the gage to read 30 amps so the readings would be off.


My new gage is stupid simple to operate.
You just hit the Only Button on the display 8 times quickly to reset it to zero. Then it keeps a running total of the Watt Hours used until you reset it again.
It's got a big capacitor inside to power the memory settings when the battery is turned off.
It's Perfect for keeping track of the battery to see if I get more out of the battery if I use it gently than when I go full speed (32 kph) into a headwind, or if it's hot or cold out.

The gage isn't waterproof, so I opened it up and sprayed it down with synthetic undercoating that protects electronics but some of it leaked onto the bulb for back-lite, and the display looks a little wonky now.

I think it looks pretty !!
Maybe the bubbles and light waves will float around like a lava lamp when it warms up?
I can stare at it for hours after I smoke a Vado.

 

[PCeBiker]

This is all granny sucking eggs here,

I had to Google that,..

My mother and grandmother didn't teach me nuthin about sucking eggs

My mom is in her 90's and grew up during the depression.
We learned how to blow eggs in school to empty them out so we could paint Easter eggs that wouldn't spoil.

I didn't even think of sucking the egg?
So I gave er a go.

I used a thumb tack to make a hole in both ends of the egg and started blowing. It worked, but my face turned red, my ears popped, and I started to pass out.

Sucking on it was WAY Easier.
The texture and flavor changes when you start sucking the yolk out.

Forget painting the shell.
I'm going to fill it with chocolate milk, seal it up and swap it into a tray of eggs at the grocery store.


PS. DON'T SUCK A GREEN EGG !!
Them Ones Be Rottin !!

I haven't encountered a rotten egg in over 50 years. Shaking the egg first can help to tell if it's rotten. A rotten egg is watery inside and feels different. Then sniff the hole after you poke you pin in it. Don't Suck On It If It Stinks !!

 

[PCeBiker]

,.. in theory, the buck converter will maintain both voltage and current at a constant level.
,.. In theory, a buck converter should be able to maintain constant voltage and current until the battery LVC cuts out.
,.. it's difficult to know how the controllers on e-bikes would react.

It's not just a theory, it's a reality.
As long as you don't have a proprietary battery/controller with all that handshake, AI, data wire crap, it'll work fine as long as the buck converter can deliver enough amps to the controller at the correct voltage.

I can run my ebike off my bench power supply as long as I don't draw more than the 3 amp limit of my power supply.

With a little design modification, e-bike controllers could do this internally. I know the controllers on some bikes already do, but unfortunately, most don't.

You've got a proper waterproof, fully potted "Industrial Strength" 12 Volt Buck converter there, probably built for the automotive industry?

I spent HOURS Surfing around the internet looking for a 48 Volt version of such a device with no luck.

There might be something designed to pimp out a golf cart that can deal with the abuse that drunken golfers can throw at it, but I couldn't find one.

I did find a high quality MeanWell Buck Converter, but it wasn't potted and had a cooling fan. (That would blow water and dirt into it.)
And the constant vibration of an ebike would break it.


I've got a 1200 Watt 20 Amp 60 Volt Buck Converter.
It's the same one that @Gionnirocket used to make his battery charger,..

https://a.aliexpress.com/_mNJrHjv

It will take any input from 6-70 Volts and convert it into any voltage from 0-60 Volts, but there's no damn way I'm gunna plug that thing into my ebike.

Yeah sure, it's got all kinds of safety features, but it's probably even More Dangerous than those ten dollar battery blenders?

There's no way I'm gonna try pushing 1250 Watts through that thing, unless I pimped it out with thermally conductive paste and fully potted it, then put it inside a blast proof box mounted nowhere near the battery, controller, or me.


I still might try it though?
Blowing s*it up up is fun, but I'd only want to sacrifice the converter to the experiment, not the rest of my ebike, or myself, or my house.



The specs do look pretty good on paper, so in theory it should work safely, but it's designed for indoor use. (But even then I wouldn't use it unattended indoors.)

You can pick the output voltage using the DIP Switch to select either 36V or 48V depending on your battery/motor,..

Or better yet, set it to NC and dial up whatever voltage you want to send into the controller.

So I'm thinking 54.6 Volts like the controller is designed to deal with from a fully charged 48V battery,..

Then set overvoltage protection to 54.6 Volts as well so the voltage shouldn't go over that voltage (like if you bump the dial by accident.)


I wouldn't turn the voltage up any higher because Almost All 48 volt controllers use 60 volt capacitors, and feeding them 54.6 volts is even kinda too much.

A well designed circuit normally leaves 20% headroom for capacitors and 60 Volts minus 20% is 48 Volts.



I've got a cheap voltage supply powering my LED light strips that had a bad solder joint on a capacitor that could have started a fire,..

And I've got a battery charger that's always on and plugged into my e-bike in the shed that's not looking too happy ,..

I don't care though.
It's an automatic charger that maintains a SLA battery so if it crapps out on me, I'm just out a $120 set of batteries that have turned into toxic waste. They might crack and leak acid all over my ebike, but it's a piece of crap anyway and I don't care.

It's been plugged in for over 3 years straight except when I go to get groceries.

I used Polarized two prong extension cords to make my battery connectors and wired it so that I can't plug my battery into the 120 VAC outlet.
I did however connect a Polarized two prong plug to the output of my charger, so I could plug the charger into the 120 VAC outlet, then plug the output of the charger into the same 120 VAC outlet as well.

That aughta blow sumthin up Real Good ?

And I found out recently that a fully charged lead acid battery is still good to go at -40° Celsius or Fahrenheit (same temperature on both scales) so we can still possibly start are cars at -40°, but a discharged battery (around 10 Volts) can freeze at around -2 or -3 Celcius.
So it's good to keep it plugged in.

 

[Gionnirocket]

Well if you gonna get froggy.... Fuse it!

 

[PCeBiker]

Well if you gonna get froggy.... Fuse it!

Yeah, I bought the fancy DC fuses with the fuse holders.
They're for high current solar DC charge controllers, but they're Honkin Huge,..

I think our Buck Converters are described as "Solar Charge Controllers" too?

 

[Chargeride]

It's not just a theory, it's a reality.
As long as you don't have a proprietary battery/controller with all that handshake, AI, data wire crap, it'll work fine as long as the buck converter can deliver enough amps to the controller at the correct voltage.

I can run my ebike off my bench power supply as long as I don't draw more than the 3 amp limit of my power supply.




You've got a proper waterproof, fully potted "Industrial Strength" 12 Volt Buck converter there, probably built for the automotive industry?


View attachment 188338


I spent HOURS Surfing around the internet looking for a 48 Volt version of such a device with no luck.

There might be something designed to pimp out a golf cart that can deal with the abuse that drunken golfers can throw at it, but I couldn't find one.

I did find a high quality MeanWell Buck Converter, but it wasn't potted and had a cooling fan. (That would blow water and dirt into it.)
And the constant vibration of an ebike would break it.


I've got a 1200 Watt 20 Amp 60 Volt Buck Converter.
It's the same one that @Gionnirocket used to make his battery charger,..


View attachment 188339

View attachment 188340

https://a.aliexpress.com/_mNJrHjv

It will take any input from 6-70 Volts and convert it into any voltage from 0-60 Volts, but there's no damn way I'm gunna plug that thing into my ebike.

Yeah sure, it's got all kinds of safety features, but it's probably even More Dangerous than those ten dollar battery blenders?

There's no way I'm gonna try pushing 1250 Watts through that thing, unless I pimped it out with thermally conductive paste and fully potted it, then put it inside a blast proof box mounted nowhere near the battery, controller, or me.


I still might try it though?
Blowing s*it up up is fun, but I'd only want to sacrifice the converter to the experiment, not the rest of my ebike, or myself, or my house.



The specs do look pretty good on paper, so in theory it should work safely, but it's designed for indoor use. (But even then I wouldn't use it unattended indoors.)


View attachment 188344


You can pick the output voltage using the DIP Switch to select either 36V or 48V depending on your battery/motor,..


View attachment 188341

Or better yet, set it to NC and dial up whatever voltage you want to send into the controller.

So I'm thinking 54.6 Volts like the controller is designed to deal with from a fully charged 48V battery,..


View attachment 188342



Then set overvoltage protection to 54.6 Volts as well so the voltage shouldn't go over that voltage (like if you bump the dial by accident.)


I wouldn't turn the voltage up any higher because Almost All 48 volt controllers use 60 volt capacitors, and feeding them 54.6 volts is even kinda too much.

A well designed circuit normally leaves 20% headroom for capacitors and 60 Volts minus 20% is 48 Volts.



I've got a cheap voltage supply powering my LED light strips that had a bad solder joint on a capacitor that could have started a fire,..

View attachment 188345View attachment 188346View attachment 188347View attachment 188348View attachment 188349



And I've got a battery charger that's always on and plugged into my e-bike in the shed that's not looking too happy ,..


View attachment 188350View attachment 188351


I don't care though.
It's an automatic charger that maintains a SLA battery so if it crapps out on me, I'm just out a $120 set of batteries that have turned into toxic waste. They might crack and leak acid all over my ebike, but it's a piece of crap anyway and I don't care.

It's been plugged in for over 3 years straight except when I go to get groceries.


View attachment 188355View attachment 188353View attachment 188354

I used Polarized two prong extension cords to make my battery connectors and wired it so that I can't plug my battery into the 120 VAC outlet.
I did however connect a Polarized two prong plug to the output of my charger, so I could plug the charger into the 120 VAC outlet, then plug the output of the charger into the same 120 VAC outlet as well.

That aughta blow sumthin up Real Good ?

And I found out recently that a fully charged lead acid battery is still good to go at -40° Celsius or Fahrenheit (same temperature on both scales) so we can still possibly start are cars at -40°, but a discharged battery (around 10 Volts) can freeze at around -2 or -3 Celcius.
So it's good to keep it plugged in.

Can I turn that into a book

 

[PCeBiker]

Can I turn that into a book

Sure, as long as I don't have to type it out again.
I type with one finger on my smartphone.
Those posts took me half a day.

 

[Gionnirocket]

Yeah, I bought the fancy DC fuses with the fuse holders.
They're for high current solar DC charge controllers, but they're Honkin Huge,..


View attachment 188360



I think our Buck Converters are described as "Solar Charge Controllers" too?

This is what I'm using.

I just installed a 4a on my bike to run lights and a small air pump.

https://www.newark.com/c/circuit-protection/fuses-fuse-accessories/fuses/automotive-fuses/prl/results?product-range=fks-ato-series

I have a thread on these somewhere on here but the search function is flock'd

 

[PCeBiker]

This is what I'm using.

They look like regular automotive fuses? I've got a whole bunch of them in my dead car sitting in the driveway, but they are only 12 volt fuses.

I remember buying a bunch of automotive fuses at the dollar store a decade or so ago.
They were made with shitty plastic that melted from the heat without the fuse blowing.

The higher voltage fuses appear to be ceramic or something?
They're not regular see through plastic.
Can you even tell when they're blown by looking at them, or do you have to test them ?

I remember old-school ~100 amp main fuses for fuse panels that appeared to be made from the same material.

 

[Gionnirocket]

They look like regular automotive fuses? I've got a whole bunch of them in my dead car sitting in the driveway, but they are only 12 volt fuses.

I remember buying a bunch of automotive fuses at the dollar store a decade or so ago.
They were made with shitty plastic that melted from the heat without the fuse blowing.

The higher voltage fuses appear to be ceramic or something?
They're not regular see through plastic.
Can you even tell when they're blown by looking at them, or do you have to test them ?

I remember old-school ~100 amp main fuses for fuse panels that appeared to be made from the same material.

They're like a Nylon material.
I haven't blown one yet so I don't know if there will be any physical signs other than what it's feeding isn't working. They state having inner arch quenching material so it may not show any sign of being blown. Probably also depends on the cause.... Short or overload.
I have a 20a on my BBS motor and another 4a on its accessories.
And now a 4a on my Zen accessories.


They're physically much more robust than cheap auto fuses.

 

[Chargeride]

My Em3v battery has one of them inside the case, lots of arcing and poor contacts when pulling 30 amps.

 

[Gionnirocket]

My Em3v battery has one of them inside the case, lots of arcing and poor contacts when pulling 30 amps.

Sounds like cheap hardware.
30a and above have been used in autos for decades

 

[Chargeride]

Well theyve probably done me a favour.

 

[6zfshdb]

I spent HOURS Surfing around the internet looking for a 48 Volt version of such a device with no luck.

I've been eyeing this one:

https://www.aliexpress.us/item/3256804167965692.html?src=google&pdp_npi=4%40dis%21USD%21131.45%21131.45%21%21%21%21%21%40%2112000028875107270%21ppc%21%21%21&src=google&albch=shopping&acnt=708-803-3821&isdl=y&slnk=&plac=&mtctp=&albbt=Google_7_shopping&aff_platform=google&aff_short_key=UneMJZVf&gclsrc=aw.ds&albagn=888888&ds_e_adid=&ds_e_matchtype=&ds_e_device=c&ds_e_network=x&ds_e_product_group_id=&ds_e_product_id=en3256804167965692&ds_e_product_merchant_id=108148150&ds_e_product_country=US&ds_e_product_language=en&ds_e_product_channel=online&ds_e_product_store_id=&ds_url_v=2&albcp=19999502313&albag=&isSmbAutoCall=false&needSmbHouyi=false&gad_source=1&gclid=Cj0KCQiAkJO8BhCGARIsAMkswyitUTjzu1sGgB8qi0CH20xBCpeQqwfzkZ6KQDZx3bGk0X6DkAJcGNQaAoOEEALw_wcB&gatewayAdapt=glo2usa#nav-description

With this buck converter, you could use a 48V motor with a 72V battery. Depending on the tolerance of the converter, you might also be able to use a 52V battery. The idea would be to wire it between the battery and the 48V bike controller.

It's large, heavy & pricey and about the same size & weight as the cordless tool battery I carry as a range extender. Not sure I want to spend that kind of $$ on an experiment.

 

[Gionnirocket]

Just looking at that giant 900 gram heat sink would cause me to run.... so give me two more pounds of cells in parallel any day.
Then add that it's additional hardware that could fail and keeping it simple seems like a good enough reason to not.

 

[PCeBiker]

Just looking at that giant 900 gram heat sink would cause me to run.... so give me two more pounds of cells in parallel any day.
Then add that it's additional hardware that could fail and keeping it simple seems like a good enough reason to not.

I agree.

Maybe there's a 30 amp version that would suit my needs better?

I've got a 30 amp BMS and my controller has a maximum draw of about 21 amps.

I like the fully potted, cast aluminum case though.
I'd be nice to find a 30 amp version with adjustable inputs and outputs.

Setting the output to something like 52 volts would make sense to me with a fully charged 48 volt battery putting out 54.6 volts.

It seems counter productive to have the output locked at 48 volts when the controller is used to seeing 54.6 volts.


And, I kinda like the way I can feel my ebike getting tired.
I can tell when it's time to head home or change the battery.

There's no need for all the programming interference to reduce the power draw at some preprogrammed level. The bike will do it naturally as the battery gets tired.
And the battery is protected, so if you pull too many amps, the voltage sag will shut you down.

I don't have any hills to deal with though, and I think that would be the big advantage for using a Buck converter.

The motor would get full power (at say 52-54 volts) until the controller shuts you down.

My ebike just slows down for my trip home, but I'd have to push it up hills if my voltage dropped too low.

 

[6zfshdb]

Another issue with these buck converters is, they reduce the voltage to 48V. A 48V lithium battery at full charge is 54.6V, which provides a significant boost in motor performance. 48V is about equal to a battery that is discharged to just 60% of capacity. Sure, the buck converter would provide 48V for a longer period of time but at a significantly lower performance level than a fully charged 48V battery.

Of course all this is speculation and may indeed not be practical on a DIY basis. I guess my point really was, every bike maker should be able to incorporate this "voltage regulation" into their controllers for just a few extra pennies.

As mentioned above, this voltage sag is really just a minor annoyance and is easily compensated on many bikes by just bumping up the PAS level. In my case, using cruise control and pedaling to assist the bike, the problem is not noticeable at all. IMO, the problem isn't worth spending a lot of $$ to correct. I do enjoy the theoretical challenge though.