Checking Multimeter Calibration at Home

[WheezyRider]

Your PSU does seem popular, featuring on many Youtube videos. Do you charge your ebike battery using that PSU? Can it be programmed or adapted to deliver a slow rising voltage to say 42V? I should have bought one of ebikebattteries.co.uk pulse chargers while they were trading.

Why do you need to buy a lab type PSU for charging? A decent battery charger is fine once you are happy that its output voltage is correct. There is a small risk of drift over time, but if it's well made it shouldn't really be an issue. I've got chargers I bought several years ago and they still output the same voltage I set them to. You would be better off if worried about drift, adding a cicuit to cut power to the pack if the voltage goes over a fixed level. If you want to charge to a lower end point voltage, you could add a dropping diode or open up the charger and modify it internally. It will charge at constant current until it gets close to the end point voltage and then gradually ramp the current down and that is all you need.

I'm not so keen on variable output, non dedicated PSUs for charging. Eventually a knob or button will get knocked etc and then your battery will be subject to too high a voltage. I might use one for testing, but not for a permanent set up.

 

[Woosh]

I spent some time yesterday reading up about calibration of domestic digital multitesters. It turns out that very few brands would publish data on the acuracy or precision of their DVMs. The best I found is the Uni-Trend UT181A. I looked also at the OWON OW18E which has bluetooth so handy for datalogging.
On cheap DVMs, the devices can be zeroed using an inbuilt 1% precision resistor.

 

[AntonyC]

In the DC 30V to 60V range the spec'd accuracy for the OWON OW18E or Farnell's similar Multicomp MP730624 is good at 0.1%+2 but there are reports the datalogging is hard to use.

 

[guerney]

Why do you need to buy a lab type PSU for charging?

To impress girls! I've read they prefer guys who can use tools. I can already erect a shelf, so I'm partyway there. In addition, a bit of redundancy would be nice - I should buy another charger in case mine fails, else I'd be waiting weeks for delivery probably, before I can use my bike again. If my existing charger turns out to be ok, I may simply buy another of the same from the Amazon seller I bought my kit from, if I can't find a good but not too pricey alternative.

On cheap DVMs, the devices can be zeroed using an inbuilt 1% precision resistor.

There's cheap, and then there's cheap! I don't think mine has that feature, but it sounds intriguing. Do you have further details?

OWON OW18E

OWON OW18E

Not expensive:

https://www.amazon.co.uk/Bluetooth-Multimeter-Multimeters-Voltmeter-Resistance/dp/B08NJT38SF

I was looking at this which has an extra digit on the digital and a temperature function, wondering if it'd be worth using after calibration:

https://www.amazon.co.uk/Multimeter-Autoranging-40000Counts-Capacitance-Temperature/dp/B08BC6JJ67/

 

[Woosh]

There's cheap, and then there's cheap! I don't think mine has that feature, but it sounds intriguing. Do you have further details?

something I read when looking at the designs of DVMs. All DVMs have high precision shunt resistors (1% for common garden variety, 0.1% and better for high count variety, Vishay makes 0.01%), but you can only use calibration function with an external board of reference resistors on some models. I think I picked that bit of info from one of the YT videos. I am interested in datalogging facilities to work out if my battery is heading in the wrong direction. The integration of current/time plot when current is under 100mA on a 15AH pack should be an indicator. If the integrated area under the plot grows then it's bad.

 

[lenny]

https://www.amazon.co.uk/Protable-Multimeter-3-7-Inch-Ultra-light-Factories/dp/B09H2BTZNH/?th=1

 

[Woosh]

that's a good review.

 

[AntonyC]

DIY multimeter calibration
https://avdweb.nl/tech-tips/electronics/multimeter-calibration-diy

 

[guerney]

This board arrived:






I'd have preferred it being delivered contained in anti-static packaging, instead of what looks to be a bog standard plastic bag. Being an exceedingly dirty person in all respects, I took care to not contaminate any of the components with grease from my filthy foul and stinky fingers, and connected this very cheap adjustable power supply to it:

3-36V Adjustable Voltage Regulation Power Supply Adatpor Power Switching Adapter | eBay

Find many great new & used options and get the best deals for 3-36V Adjustable Voltage Regulation Power Supply Adatpor Power Switching Adapter at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

After switching on the power supply at it's lowest voltage, and leaving the reference board to warm up for 10 minutes, I set the voltage to an apparent 8.65V, and with the toggle switch on the reference board set to 4.991V... the output of my cheap uncalibrated digital multimeter read mostly 4.99V and 5.00V, but also skipping more briefly between 4.98V and 5.01V.

After toggling the switch on the reference board to 9.982V and increasing the power supply to 11.9V, the readout mostly stabilises at 9.99V, with 9.97V, 9.98V and 10.00V flashing briefly.

Adjusting my DVM's potentiometer to get more accurate results could well be very fiddly (if it has an adjustable potentimeter, haven't looked yet). Not bad for a cheapo?

 

[saneagle]

This board arrived:


View attachment 53893



I'd have preferred it being delivered contained in anti-static packaging, instead of what looks to be a bog standard plastic bag. Being an exceedingly dirty person in all respects, I took care to not contaminate any of the components with grease from my filthy foul and stinky fingers, and connected this very cheap adjustable power supply to it:

3-36V Adjustable Voltage Regulation Power Supply Adatpor Power Switching Adapter | eBay

Find many great new & used options and get the best deals for 3-36V Adjustable Voltage Regulation Power Supply Adatpor Power Switching Adapter at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

After switching on the power supply at it's lowest voltage, and leaving the reference board to warm up for 10 minutes, I set the voltage to an apparent 8.65V, and with the toggle switch on the reference board set to 4.991V... the output of my cheap uncalibrated digital multimeter read mostly 4.99V and 5.00V, but also skipping more briefly between 4.98V and 5.01V.

After toggling the switch on the reference board to 9.982V and increasing the power supply to 11.9V, the readout mostly stabilises at 9.99V, with 9.97V, 9.98V and 10.00V flashing briefly.

Adjusting my DVM's potentiometer to get more accurate results could well be very fiddly (if it has an adjustable potentimeter, haven't looked yet). Not bad for a cheapo?

Now all you need is an oscilloscope to see how much ripple you get from your charger, then decide whether you're going to use the top, middle, bottom or RMS value, and don't forget to use a co-ax cable between your probes and oscilloscope, otherwise you'll be measuring a ripple induced into the leads by the mains in your house. You can have hours of fun with this. No need to actually ride your bike, so your battery will last even longer.

How do you reduce voltage ripple?

Ripple voltage means the amount of AC voltage that appears on a DC voltage. The main reason for the ripple voltage is that the converter converts the AC voltage into a DC voltage, but the AC voltage cannot completely eliminate.

www.powerctc.com

 

[WheezyRider]

This board arrived:


View attachment 53893



I'd have preferred it being delivered contained in anti-static packaging, instead of what looks to be a bog standard plastic bag. Being an exceedingly dirty person in all respects, I took care to not contaminate any of the components with grease from my filthy foul and stinky fingers, and connected this very cheap adjustable power supply to it:

3-36V Adjustable Voltage Regulation Power Supply Adatpor Power Switching Adapter | eBay

Find many great new & used options and get the best deals for 3-36V Adjustable Voltage Regulation Power Supply Adatpor Power Switching Adapter at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

After switching on the power supply at it's lowest voltage, and leaving the reference board to warm up for 10 minutes, I set the voltage to an apparent 8.65V, and with the toggle switch on the reference board set to 4.991V... the output of my cheap uncalibrated digital multimeter read mostly 4.99V and 5.00V, but also skipping more briefly between 4.98V and 5.01V.

After toggling the switch on the reference board to 9.982V and increasing the power supply to 11.9V, the readout mostly stabilises at 9.99V, with 9.97V, 9.98V and 10.00V flashing briefly.

Adjusting my DVM's potentiometer to get more accurate results could well be very fiddly (if it has an adjustable potentimeter, haven't looked yet). Not bad for a cheapo?

Is the meter on the 20 V or 200 V range?

 

[guerney]

Is the meter on the 20 V or 200 V range?

200V

 

[WheezyRider]

200V

That's reassuring to know your meter is reasonably accurate.

 

[AntonyC]

If this is the XL830L the 200V range only resolves to 0.1V. It's best to calibrate as near as you can get to the voltage you want to measure and using the same range, but I haven't found a reference above 10V off the shelf.

 

[guerney]

If this is the XL830L

It is.

If this is the XL830L the 200V range only resolves to 0.1V. It's best to calibrate as near as you can get to the voltage you want to measure and using the same range, but I haven't found a reference above 10V off the shelf.

I did idly wonder about that while using this reference board, and made a lazy mental note to search.

 

[guerney]

BTW The XL830L is also reasonably accurate measuring these reference resistors.

 

[WheezyRider]

It is.




I did idly wonder about that while using this reference board, and made a lazy mental note to search.

I'm confused, so if your DVM can only resolve to 0.1 V on the 200 V range, were the measurements you quoted above on the 20 V range after all?

 

[WheezyRider]

If this is the XL830L the 200V range only resolves to 0.1V. It's best to calibrate as near as you can get to the voltage you want to measure and using the same range, but I haven't found a reference above 10V off the shelf.

Could you put 4x 10 V references in series, powered by separate battery supplies? Would that just amplify the error, or could you measure each reference in the chain and also the overall voltage and compare?

 

[guerney]

I'm confused, so if your DVM can only resolve to 0.1 V on the 200 V range, were the measurements you quoted above on the 20 V range after all?

Nope, in the 200V range.

 

[guerney]

I'm confused, so if your DVM can only resolve to 0.1 V on the 200 V range, were the measurements you quoted above on the 20 V range after all?

Apologies, I swear my Central Serous Retinopathy addled eyes will be the death of me someday.

Without a warmup period, @9.982V reference, shows 10V mostly:







Steady 10V: