Calling all math majors

[PCeBiker]

It would generate less and dissipate more heat under low current conditions. Therefore, there would be less variation in resistance.

That's what I was thinking, but I thought that if it gives off 750 mv at 500 amps, then it probably gives off something like (20÷500) 4% of the needles full scale movement at 20 amps, so the accuracy would suck.
Even if that signal were sent into a digital ammeter, then the accuracy of the meter comes into play, and even the length and the resistance of the wire feeding the signal.

And I can't set my digital meter to 500 amp scale so I'd have to recalibrate the readings.

A 30 amp shunt would be Perfect because my ebike apparently draws just over 20 amps, but I don't have a 30 amp choice on my digital meter.

 

[PCeBiker]

Never did comparison to other Lithium chemistry; comparison was to lead acid in RV application.

So for reference sake,.. my 48v 25ah li-ion battery weighs ~14.4 pounds (measured on a bathroom scale with the same accuracy issues as the ammeter. )

How much would a 1200 Watt hour LPF battery weigh?

 

[Roamers]

So for reference sake,.. my 48v 25ah li-ion battery weighs ~14.4 pounds (measured on a bathroom scale with the same accuracy issues as the ammeter. )

How much would a 1200 Watt hour LPF battery weigh?

As I recall my 12V nominal 100 Ahr batteries weigh 31 # each.

 

[Roamers]

4% of the needles full scale movement at 20 amps, so the accuracy would suck

I'd compare it to tire pressure gauges: mid scale is good. Our Sprinter and ebikes use the same gauge. Car has a different (lower max) gauge. Pressure gauge for old touring bike (110 psi tires) would suck for current applications.

 

[PCeBiker]

I'd compare it to tire pressure gauges: mid scale is good.

That's what I did with my bathroom scale.

I didn't weigh the battery.
I weighed myself, then I weighed myself holding the battery.

 

[PCeBiker]

Pressure gauge for old touring bike (110 psi tires) would suck for current applications.

I remember thinking that my Tracker had no air pressure in the tires.

I had lowered the pressure for the dirt to about 25 PSI, and it wasn't enough pressure to push the metal plunger gauge even though the scale started at 20, on the ~160 PSI scale.


I do use this one though on my e-bike,..

It might not be very accurate for my tires, but it's just for emergencies and it doesn't need to be that accurate when fixing a roadside flat.

It's for my air shocks, but works great as a micro pump other than the long handle, but it needs a long handle to pump up to over 200 psi, and it's Way easier to inflate a flat tire with a long throw handle than my standard short throw bike pump,..

 

[6zfshdb]

That's what I was thinking, but I thought that if it gives off 750 mv at 500 amps, then it probably gives off something like (20÷500) 4% of the needles full scale movement at 20 amps, so the accuracy would suck.
Even if that signal were sent into a digital ammeter, then the accuracy of the meter comes into play, and even the length and the resistance of the wire feeding the signal.

And I can't set my digital meter to 500 amp scale so I'd have to recalibrate the readings.

A 30 amp shunt would be Perfect because my ebike apparently draws just over 20 amps, but I don't have a 30 amp choice on my digital meter.

FWIW, I originally bought the 100A version of that gauge before I discovered the 50A model. when I compared the accuracy of the two, I saw very little difference in the 0 to 40 amp range. Both were within 5% when measured using my bench power supply.

Not sure if it would be the same for the 500A version though.

 

[PCeBiker]

FWIW, I originally bought the 100A version of that gauge before I discovered the 50A model.

I did the same thing.

I remember that you told me about your 50 amp shunt after I bought mine.

I didn't buy the proper 50 amp shunt for it because it was Way Off Scale, reading 8700 ah, when it's supposed to read 87.00 ah.

Reading glasses would have fixed the problem but I decided to try and find something else.

 

[PCeBiker]

There is also a 48V LiFePO4 version, which may give better results.

https://www.amazon.com/gp/product/B0DJ9SKY2Q/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

I'll have to play around with that one. Probably wouldn't require any padding for a 48V bike.

That one doesn't ship to Canada??

I'm thinking that that it may not need a padding resistor, but it might have a compressed scale, because a LiFePO4 battery doesn't have as many usable volts?

 

[6zfshdb]

I did the same thing.

I remember that you told me about your 50 amp shunt after I bought mine.

I didn't buy the proper 50 amp shunt for it because it was Way Off Scale, reading 8700 ah, when it's supposed to read 87.00 ah.

Reading glasses would have fixed the problem but I decided to try and find something else.

Yeah, that decimal point is hard to read. I find it a bit easier in sunlight with the backlight off.

 

[6zfshdb]

That one doesn't ship to Canada??

I'm thinking that that it may not need a padding resistor, but it might have a compressed scale, because a LiFePO4 battery doesn't have as many usable volts?

I just ordered one just for the heck of it. I'll test it to see if there is a significant difference over the 48V version. If so, and if you're interested, I can always order another and ship it to you from here.

The 48V version with a padding resistor is so close to being perfect, I don't expect much of an improvement with the LiFePO model.

The only thing I'd like to see is more useful range on the scale. At 42V, the needle is about centered in the red zone. It would be nice if it went all the way to the pin. The same is true in the white zone on the fully charged end of the scale.

 

[PCeBiker]

I just ordered one just for the heck of it. I'll test it to see if there is a significant difference over the 48V version.

I'm kinda thinking that the scale is going to be off compared to my 48V version?
My numbers seem to line up OK, with 40V being just into the red, and 54V being right at the start of red at the top end.

The 48V LiFePO meter is the only LiFePO meter, so their should be a difference between the two 48V meters.

If so, and if you're interested, I can always order another and ship it to you from here.

I'm just curious.
If I had a LiFePO4 meter, then I'd have to buy the LiFePO4 batteries to go with it, and they cost more than the meter.

The 48V version with a padding resistor is so close to being perfect, I don't expect much of an improvement with the LiFePO model.

I'm thinking it might go into the red sooner? At least at the low end?

And considering how a1V variation makes a Huge Difference when it comes to Li-Ion batteries, I'm thinking that the meters operate differently,

The only thing I'd like to see is more useful range on the scale. At 42V, the needle is about centered in the red zone. It would be nice if it went all the way to the pin. The same is true in the white zone on the fully charged end of the scale.

Well,.. being as you skewed the scale with your padding resistor, maybe the same resistor might skew the LiFePO meter further towards the pin?

I remember choosing 42V as my personal Empty mark because my batteries are pretty much toast below that, so it would be better for me to see the start of the red at that voltage.

I consider the start of the green at 48V a bit late too.
I'd like something like 50V as more of a half way point.


If the 48V LiFePO meter ends up being scaled more to my personal preference then yeah, I'll take you up on your offer.
The meters are $50 up here but all I can find is the 48V 100 amp (regular) meters.

There's 3 of them that look exactly the same but with a different brand name.
(Yours has a different name than mine, and I found one other.)


Ohh,.. I'm thinking that the quality of the shunt has more to do with an accurate reading than the quality of the meter, but that's a guess.

I'm not too sure about the meter I want to install?
The built-in shunt might be more susceptible to heat and maybe humidity variations?

 

[spokewrench]

There may actually be an advantage to using that 500A shunt.


It would generate less and dissipate more heat under low current conditions. Therefore, there would be less variation in resistance. The question then becomes what is it's accuracy in the 0 to 40A range.

Looks like another experiment to fool around with.

With a simple Hall Effect meter, if you want 10 times more sensitivity, you just wrap the amp conductor 10 times through the donut.

 

[6zfshdb]

With a simple Hall Effect meter, if you want 10 times more sensitivity, you just wrap the amp conductor 10 times through the donut.

Tricky to do though, with 10 gauge wire. Then try and fit it into a housing on the bike.

 

[6zfshdb]

I'm kinda thinking that the scale is going to be off compared to my 48V version?
My numbers seem to line up OK, with 40V being just into the red, and 54V being right at the start of red at the top end.

The 48V LiFePO meter is the only LiFePO meter, so their should be a difference between the two 48V meters.



View attachment 189495



I'm just curious.
If I had a LiFePO4 meter, then I'd have to buy the LiFePO4 batteries to go with it, and they cost more than the meter.



I'm thinking it might go into the red sooner? At least at the low end?

And considering how a1V variation makes a Huge Difference when it comes to Li-Ion batteries, I'm thinking that the meters operate differently,




Well,.. being as you skewed the scale with your padding resistor, maybe the same resistor might skew the LiFePO meter further towards the pin?

I remember choosing 42V as my personal Empty mark because my batteries are pretty much toast below that, so it would be better for me to see the start of the red at that voltage.

I consider the start of the green at 48V a bit late too.
I'd like something like 50V as more of a half way point.


If the 48V LiFePO meter ends up being scaled more to my personal preference then yeah, I'll take you up on your offer.
The meters are $50 up here but all I can find is the 48V 100 amp (regular) meters.

There's 3 of them that look exactly the same but with a different brand name.
(Yours has a different name than mine, and I found one other.)


Ohh,.. I'm thinking that the quality of the shunt has more to do with an accurate reading than the quality of the meter, but that's a guess.

I'm not too sure about the meter I want to install?
The built-in shunt might be more susceptible to heat and maybe humidity variations?

Well, it turns out that LiFePO meter isn't suitable for a 52V e-bike, even less so for 48V systems. No padding resistance was used in the readings below.

It looked promising at 58.8V, max for a 52V battery:

But the lowest voltage the meter will read is 47V, which is still 30% SOC for a 52V battery and close to 50% for a 48V:

At 50% SOC, 50.4V for a 52V battery, the gauge reads on the red / green border:

I don't see how this meter can be used with any 48V LiFePO battery system unless additional circuitry is involved. It may be designed for a specific vehicle.

The meter pegs on the high end at just under 62V. Rater than return it, I'll see if it's of any use with a padding resistor on my 72V fork lift.

 

[PCeBiker]

Thanks for the report.
I guess that I don't want one then?

I do like how it's showing and empty tank before you're actually empty, but that's a bit more of a skewed scale than I want.
It's better than reading half a tank when your controller shuts down though.

 

[PCeBiker]

I don't see how this meter can be used with any 48V LiFePO battery system unless additional circuitry is involved. It may be designed for a specific vehicle.

I don't understand that at all?

Maybe golf carts are different somehow, but they would all have to be different in the same way to use that meter.

 

[spokewrench]

I don't understand that at all?

Maybe golf carts are different somehow, but they would all have to be different in the same way to use that meter.

$5 for a 1ma movement. A zener to set where it will read 0. A resistor to determine full scale. Maybe the only problem if it got wet would be the paper scale you draw. So treat the paper with airplane dope, or fix it with a connector and temporary handlebar clips so you can pocket it in the event of rain.

 

[6zfshdb]

Thanks for the report.
I guess that I don't want one then?

I do like how it's showing and empty tank before you're actually empty, but that's a bit more of a skewed scale than I want.
It's better than reading half a tank when your controller shuts down though.

Yeah, it's only useful for the first half of the battery capacity.

 

[6zfshdb]

I don't understand that at all?

Maybe golf carts are different somehow, but they would all have to be different in the same way to use that meter.

Me either unless the meter I received is defective.