Turnigy power meter accuracy

[Pedalo]

I've been watching the power pushed in during charging and taken out during riding of my E-brompton with A123 battery pack.

I've got a Turnigy power analyser placed in the circuit to measure it.

I was expecting to see total power fed in to be roughly the same, or a little higher than power out - to account for losses due to heat etc.

Instead I see quite consistently more power taken out than I put in! Typically I see 40 watt hours going in but 50 coming out.

I would like to think these A123 cells are magic but instead I guess I should conclude there must be some considerable inaccuracy in the measurement.

Possibilities:

The current going in is at about 1A continuous. This is quite low compared to the total range over which the meter can measure so it may be that measurements with low current are quite inaccurate.

Power out is quite bursty. The inaccuracy could be due to how the meter samples and averages power measurements over time.

Comments?, Anyone else seen similar anomalies?

 

[Pedalo]

Ooh I just found this which might help to accout for it...

YouTube - Watts Up vs Turnigy wattmeter

 

[jerrysimon]

If you check my battery build thread I played around with the Turnigy and had some inconsistant readings too.

I have not really used the meter since those early days when I wanted to see typical current draw etc.

Mostly now I use the Cellog to confirm that that cells remain in balance. As discussed since first balancing them with my more expensive balance/charger (this now too sits on the shelf unused) now instead they are being charged daily by my cheap Chinese 36v charger.

Regards

Jerry

 

[onmebike]

Ooh I just found this which might help to accout for it...

YouTube - Watts Up vs Turnigy wattmeter

I'm not sure how useful this test is?
The Watts up meter is monitoring power used by the Turnigy circuit so the readings of the two meter's will never match.
How much of the 300ma power supply is being used to power the two meter's?
Would there be enough left to charge the battery?
If the battery is fully charged, would the Turnigy register anything?
It may have been useful had the meters been switched round for a comparison.
Could the inconsistancy between power in/power out mentioned in the original thread be due to the differences between power source's? Constant in the case of Charger and variable in the case of the battery. Just a thought.

 

[onmebike]

I've been watching the power pushed in during charging and taken out during riding of my E-brompton with A123 battery pack.

I've got a Turnigy power analyser placed in the circuit to measure it.

I was expecting to see total power fed in to be roughly the same, or a little higher than power out - to account for losses due to heat etc.

Instead I see quite consistently more power taken out than I put in! Typically I see 40 watt hours going in but 50 coming out.

I would like to think these A123 cells are magic but instead I guess I should conclude there must be some considerable inaccuracy in the measurement.

Possibilities:

The current going in is at about 1A continuous. This is quite low compared to the total range over which the meter can measure so it may be that measurements with low current are quite inaccurate.

Power out is quite bursty. The inaccuracy could be due to how the meter samples and averages power measurements over time.

Comments?, Anyone else seen similar anomalies?

I'm no expert so I may be wrong. Wouldn't the discrepancy between power in and power out be explained by the higher discharge current on power out?
The power source's are different for both calculation's which may also help explain the discrepancy. The constant voltage from the charger may differ from the battery voltage which also drops as it discharges.

 

[NRG]

Unfortunatley no, if you discharge X amount of energy from the battery you will need to replace with X amount of energy...you can't make or generate more energy out of nothing. The charger however, as it is not 100% efficient, may well pull more energy from the mains than it puts into the battery.

The Turnigy is inaccurate hence the discrepancy, the watts up I use is just about bang on for energy out vs energy in.

This reminds me of those so called energy saving devices that lower the mains voltage from 230~240 volt down to 220v to 'save you energy' what they don't tell you is that it takes the same amount of energy to boil a pint of water in a kettle from room temperature at 220v vs 240v all that changes is the time it takes!

 

[onmebike]

Unfortunatley no, if you discharge X amount of energy from the battery you will need to replace with X amount of energy...you can't make or generate more energy out of nothing. The charger however, as it is not 100% efficient, may well pull more energy from the mains than it puts into the battery.

The Turnigy is inaccurate hence the discrepancy, the watts up I use is just about bang on for energy out vs energy in.

This reminds me of those so called energy saving devices that lower the mains voltage from 230~240 volt down to 220v to 'save you energy' what they don't tell you is that it takes the same amount of energy to boil a pint of water in a kettle from room temperature at 220v vs 240v all that changes is the time it takes!

I know you can't take out more than the charger put's in. Unless you have regenerative braking.
I thought the figure's referred to one hour of use for some strange reason. Probably the drugs.

 

[onmebike]

Unfortunatley no, if you discharge X amount of energy from the battery you will need to replace with X amount of energy...you can't make or generate more energy out of nothing. The charger however, as it is not 100% efficient, may well pull more energy from the mains than it puts into the battery.

The Turnigy is inaccurate hence the discrepancy, the watts up I use is just about bang on for energy out vs energy in.

This reminds me of those so called energy saving devices that lower the mains voltage from 230~240 volt down to 220v to 'save you energy' what they don't tell you is that it takes the same amount of energy to boil a pint of water in a kettle from room temperature at 220v vs 240v all that changes is the time it takes!

I'm still not getting my head round these figure's? 40wh going in versus 50wh coming out.
Watt hour's refer's to power in watts multiplied by time in hour's. A 60watt light bulb running for 3 hour's = 180wh.
40wh going in seem's far to low for the complete charging process as a 42volt 1amp charge as quoted is approx 40-42watts per hour, if charging take's
6hrs the figure in watt hours should be more like 240-252wh. I'd also expect to see more than 50wh from a fully charged battery. Thats approx 250w for 12 mins?
I can only conclude the figures are wrong.
Can someone explain where I'm mistaken please, if that is the case?

 

[Pedalo]

I'm still not getting my head round these figure's? 40wh going in versus 50wh coming out.
Watt hour's refer's to power in watts multiplied by time in hour's. A 60watt light bulb running for 3 hour's = 180wh.
40wh going in seem's far to low for the complete charging process as a 42volt 1amp charge as quoted is approx 40-42watts per hour, if charging take's
6hrs the figure in watt hours should be more like 240-252wh. I'd also expect to see more than 50wh from a fully charged battery. Thats approx 250w for 12 mins?
I can only conclude the figures are wrong.
Can someone explain where I'm mistaken please, if that is the case?

Sorry if it wasn't clear.

Starting from a fully charged battery I ride my bike to work. It takes approx half an hour and during that time power countinuously varies from zero to about 500W. The Wh figure that my Turnigy meter shows has been taken out of my battery at the end of my journey is approx 50Wh. If you were to draw a graph of power vs time, the Wh figure should represent the area under the line or the total energy taken out of the battery.

When I get to work I recharge my battery again. This time I reverse the Turnigy to now measure power going back into the battery. In this case it takes about an hour to fully charge it up again and is charging at a near constant 40W. And in fact the Wh figure shown on the Turnigy is indeed 40Wh.

(BTW the total capacity of my battery is approx 90Wh - very small for an ebike!)

So there is some kind of discrepancy. I was expecting energy taken out of the battery to be smaller than that going in - so I must conclude that the Turnigy meter isn't very accurate.

 

[NRG]

Yes, something is amiss with the Turnigy, compare that with the watts up...my ride on Tuesday drew 211wh from the battery and on charge 220wh was put in, the difference being due to the HobbyCity battery medics I use to balance out the pack at full charge.

 

[onmebike]

My first mistake was not realizing the a123 battery pack is only 2.3a.
Second was thinking you were running down the battery completely before charging.
I can now see why the figures confused me.
Being that the Turnigy measures on the load side and therefore doesn't measure it's own minimal consumption, it should show more going in than coming out.
I understand that WH are watts x hours which is reflected in the figure's for 1 hours charging at 40watts = 40wh, but how does the meter equate the wh for only half hours use? I know it update's the wh at 0.4 second intervals but thats about all.
I was thinking it was just using it quicker than storing it, being that time is part of the equation, but I now see my error.
Bugger, I just bought one.

 

[onmebike]

I've come up with a theory that may be absolute nonsense but I'll share it anyway.
The figures quoted in original thread of 40wh power in 50wh power out?
I assume the meter does the equations based on watts x hours = WH.
In the case of power in the figures, 1hrs charge at 40watts = 40wh as correctly displayed on the meter.
In the case of power out the figure was 50wh for less than an hours use?
My theory is, because the discharge process was less than 1 hour, the meter may be displaying what power would be consumed had the process run for an hour?
This may be nearer the true figure's, 50watts x 0.8 hours running time = 40WH? This would then appear to shown power in, equals power out.
Its only a theory based on not knowing how the meter equates watts x hours for measurements below 1 hour.
Putting 40watts in over an hour = 40WH
Taking 40watts out in 48 minutes = 50WH?
Is it the way the meter displays it that confuse's.

 

[NRG]

The calculation for battery wh is ah x volts, all these meters are doing is to accumulate the wh used by measuring the ah used x the voltage. The Turnigy seems to have an issue in this respect hence the discrepancy.

 

[onmebike]

The calculation for battery wh is ah x volts, all these meters are doing is to accumulate the wh used by measuring the ah used x the voltage. The Turnigy seems to have an issue in this respect hence the discrepancy.

I'm not sure about this. The way I understand it Volts x amps x time[In hours] = WH.
In the case of a battery it is only true because the battery has a fixed capacity. A 12volt 1a psu run for 2 hours = 24WH, watts x time?
The battery refered to in this thread I assume is 36v 2.3ah or 82.8watts, its not being run down completely so the WH can be worked out by watts consumed x time run. 40watts consumed in 48mins = 50watts in 1hour or 50WH. The meters not telling you the total watts consumed but the rate at which its being consumed. The same for the charging process 40w x 1 hour = 40WH, had the process taken 2hours it would have been 80WH.
Its probably wrong but that's my theory. When I get time I'll experiment.

 

[NRG]

I guess you'll have to wait for your Turnigy to arrive before you are convinced, however, 36v x 2.3Ah is 82.8wh The amps are already in Ah, 36v x 2.3A is 82.8 Watts... The meter does tell you the Wh used no way is it showing the rate. If I was consuming the rate shown in my pictures below I would have a serious problem!

I could search futher on Goolge but these will do:

calculate battery wh - Google Search

Measuring the Capacity of a Battery - Storage

From Ebikes.ca:

Watt Hours

The figure that matters most when comparing how far a given battery pack will take you is not the amp-hour capacity but the total energy stored watt-hours. To make things more familiar, one watt-hour is one-thousandth of a kWh, the unit of energy used to measure household electrical usage. The watt-hours stored in a battery pack is approximated by taking the actual amp-hours and multiplying it by the pack voltage.

A higher voltage setup therefor needs fewer amp-hours to deliver the same range. So a 24V 8Ah battery can deliver 192 watt-hours, while a 48V 4Ah pack also has 192 watt-hours. Assuming that both batteries are of the same chemistry, then you could expect they would weight the same, cost the same, and provide the same performance on appropriately designed ebikes (ie, one designed for 24V and the other for 48V).

192 watt-hours is about the smallest battery size you would want for an ebike. Many of the store-bought ebikes have about this much capacity since it keeps the battery cost down. For people who want to actually commute reasonable distances of 40-50km, then I would recommend on the order of 400 watt-hours. While it can vary a lot with usage habits, an energy consumption of 9-10 watt-hrs / km is typical on normal direct-drive setups.

Pictures showing the WU meter.

Edit, forgot to add the meter reading during charge. I charge to 4.1v / cell x 12 cells = 49.2volts so the pack here is just about fully charged, the current has tapered off, the 700mA is due to active cell balancing and the Wh (energy) put back in is the same as taken out....

 

[onmebike]

I guess you'll have to wait for your Turnigy to arrive before you are convinced, however, 36v x 2.3Ah is 82.8wh The amps are already in Ah, 36v x 2.3A is 82.8 Watts... The meter does tell you the Wh used no way is it showing the rate. If I was consuming the rate shown in my pictures below I would have a serious problem!

I could search futher on Goolge but these will do:

calculate battery wh - Google Search

Measuring the Capacity of a Battery - Storage

From Ebikes.ca:

Watt Hours

The figure that matters most when comparing how far a given battery pack will take you is not the amp-hour capacity but the total energy stored watt-hours. To make things more familiar, one watt-hour is one-thousandth of a kWh, the unit of energy used to measure household electrical usage. The watt-hours stored in a battery pack is approximated by taking the actual amp-hours and multiplying it by the pack voltage.

A higher voltage setup therefor needs fewer amp-hours to deliver the same range. So a 24V 8Ah battery can deliver 192 watt-hours, while a 48V 4Ah pack also has 192 watt-hours. Assuming that both batteries are of the same chemistry, then you could expect they would weight the same, cost the same, and provide the same performance on appropriately designed ebikes (ie, one designed for 24V and the other for 48V).

192 watt-hours is about the smallest battery size you would want for an ebike. Many of the store-bought ebikes have about this much capacity since it keeps the battery cost down. For people who want to actually commute reasonable distances of 40-50km, then I would recommend on the order of 400 watt-hours. While it can vary a lot with usage habits, an energy consumption of 9-10 watt-hrs / km is typical on normal direct-drive setups.

Pictures showing the WU meter.

I'm not disputing your being right. I just find the reference to time as in wh pointless when calculating total energy consumed. This is what I find confusing. A 12v 5a battery = 60w or wh as you say. connect a 60watt load for an hour and its 60wh, on that we agree. Connect a 30watt load for an hour and its 30wh although the battery isn't completely discharged. Same battery different load determines WH.
In the case of an ebike, 36v 10ah battery being discharged at a constant 5ah to make things simple, would run for two hours = 360WH[36v x 5a x 2hrs]. But if you only run it at 2ah for one hour the wh is 72[36v x 2a x 1hr]. Load x time determine WH. As in 100watt bulb x 3hrs = 300wh.
Am I confusing WH with W/H WH being watts x hours and W/H being Watts divided by hours. A battery could be rated as either because of its fixed capacity e.g. 12v x 2a x 1hr = 24wh or 12v x 2a/1 hour = 24w/h.
My heads hurting. Lets start on cubic feet of gas converted to kwh thats easier.

 

[onmebike]

I've now had a play with several watt meters and have come to the conclusion the terms WH and KWH basically means total watts/kilowatts consumed and the reference to time[H] is meaningless.
E.g. connect a 2200watt load and the watt section of meter displays current watts being used per hour[2200]. The WH/KWH section of the meter displays total watts consumed on an increasing scale. In the case of the 2200watt load, approx 550 after 15mins?
This is where I find it confusing. Why is the meter displaying 550WH when only 15 minutes has past? What relevance does H have?

 

[NRG]

I think you are confusing power with energy. Found this link that may help:

Watt / Watt-Hour

 

[onmebike]

I think you are confusing power with energy. Found this link that may help:

Watt / Watt-Hour

You may well be right, but even on your meter reading of 211.3WH, where's the relevance to time? I'm pretty sure that reading doesn't refer to a measurement in exact hour/s.

 

[Pedalo]

You may well be right, but even on your meter reading of 211.3WH, where's the relevance to time? I'm pretty sure that reading doesn't refer to a measurement in exact hour/s.

WH is just a measurement of energy.

When you buy a battery, it has a WH rating which shows how much energy it can store. For example my battery has a WH rating of about 90WH.

This means it can deliver 90W continuously for 1 hour or 45W for 2 hours or 180W for half an hour etc. When I attach my Wattmeter, use my bike for a while and see a reading of 45WH it means I've used half the energy in the battery. It might have been that I've used the battery at 45W for an hour, or 90W for half an hour. In actual fact when I ride my bike, the power usage continuously varies depending on how steep a hill is and how much I use the throttle. All that is important to me is if I see a reading of 45WH I know that my battery is now only half full.