Checking Multimeter Calibration at Home

[Woosh]

in that article by BMZ on the Samsung ICR18650-26F, the benefit of 4.1V charging begins to be noticeable from over 1500 full cycle discharge. Most e-bikers would use much less than 100 full cycles a year, about 5,000 miles a year from a 36V 15AH battery (full cycle discharges are cumulative, one cycle count equals 100% capacity).

 

[Woosh]

my adjustable supply cost £35 much the same as a charger.

can you do CC and CV from your PSU?

 

[guerney]

in that article by BMZ on the Samsung ICR18650-26F, the benefit of 4.1V charging begins to be noticeable from over 1500 full cycle discharge.

Well that's good news, because I usually only have enough time to charge my 19.2Ah LG MH1 celled battery to about 40V.

 

[Woosh]

the bigger capacity you have, the less benefit you'll get from charging at 40V or 41V. One full charge 36V 19.2AH = 55 miles. 2,000 miles a year = 36 full cycle charges. At that rate, there is no benefit to you because you may not live long enough (41 more years) to see the difference.

 

[guerney]

the bigger capacity you have, the less benefit you'll get from charging at 40V or 41V. One full charge 36V 19.2AH = 55 miles. 2,000 miles a year = 36 full cycle charges. At that rate, there is no benefit to you because you may not live long enough (41 more years) to see the difference.

I won't, but I'll die trying:

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[AntonyC]

can you do CC and CV from your PSU?

Yes it's the older version of this and the one I received sets voltage accurately.

RD RD6018 60V 18A DC Adjustable Step Down Stabilized Voltage Lab Variable Bench Power Supply Buck Converter

Smarter Shopping, Better Living! Aliexpress.com

vi.aliexpress.com

Direct Calibration Solutions | UKAS Accredited | ISO9001 Certified

Experience the precision of our UKAS accredited calibration laboratory in the UK. With a focus on accuracy and compliance, our expert team offers comprehensive in-house and onsite calibrations. Trust us to deliver tailored solutions, backed by industry expertise, for all your calibration needs...

www.directcalibrationsolutions.co.uk

Calibration can be pricey but I got quick tests over a narrow range and Chris gave a very fair discount.

 

[Bikes4two]

• @AntonyC - that's an interesting PSU from Ali Express that you linked to - thanks
• @Woosh asked "can you do CC and CV from your PSU? " and you said it could but from the limited blurb on the Ali listing, all I could see was that the unit is a variable voltage source rather than something like a 'smart' battery charger that intially provides a Constant Current (CC) for the majority of the charging cycle and then switches to a Constant Voltage (CV) for the final part of battery charging.
• Have I missed something from the blurb (is there a downloadable handbook somewhere?)?

 

[saneagle]

80%: what would be proof, if not evidence? Here they report test results from BMZ, and my adjustable supply cost £35 much the same as a charger.

Battery charging: Full versus Partial

Batteries are part of our lives. They are present in everyday devices such as electric cars, smartphones, tablets or laptops. For this reason it’s important to know how to treat them right. We already know that TMS (Thermal Management Systems) are important to keep batteries at recommended...

pushevs.com

100% agree that it's great that people are trying to get the details on what's going on, that could be linked to why we haven't seen battery fires on here.

That test is for cells, not a battery with BMS.

 

[AntonyC]

> That test is for cells, not a battery with BMS.

You've a knack for finding fair points that are easily overlooked But assuming the cells don't go madly out of balance.... what might make the results differ / how?

The "PSU" is a CV & CC regulator, some have guards such as Ah limits. They say "don’t need to add a diode" in series on the output, lygte says you need one if the power input fails while charging. (That's different from the anti-reversal diode they show at the end.)

Can RD POWER SUPPLY charge batteries

Hello guys, how’s your days? Today I want to show the application of our power supply. We can use DPS3005 as an example, it can provide up to 32V DC voltage and 5A current, you can use it to power on loads like LED lights, fans or somethings else. Recently some customer ask me if our power...

budgetlightforum.com

"Through the picture we can see the whole charging process, the battery charging starts with a constant current icon CC, ends with a constant voltage icon CV,. It proves that our power supply can charge lithium batteries."

 

[saneagle]

> That test is for cells, not a battery with BMS.

You've a knack for finding fair points that are easily overlooked But assuming the cells don't go madly out of balance.... what might make the results differ / how?

The "PSU" is a CV & CC regulator, some have guards such as Ah limits. They say "don’t need to add a diode" in series on the output, lygte says you need one if the power input fails while charging. (That's different from the anti-reversal diode they show at the end.)

Can RD POWER SUPPLY charge batteries

Hello guys, how’s your days? Today I want to show the application of our power supply. We can use DPS3005 as an example, it can provide up to 32V DC voltage and 5A current, you can use it to power on loads like LED lights, fans or somethings else. Recently some customer ask me if our power...

budgetlightforum.com

"Through the picture we can see the whole charging process, the battery charging starts with a constant current icon CC, ends with a constant voltage icon CV,. It proves that our power supply can charge lithium batteries."

How can you assume that the cells won't go madly out of balance, when you've prevented the balancing system from working?

 

[WheezyRider]

How can you assume that the cells won't go madly out of balance, when you've prevented the balancing system from working?

Because if you start with quality matched cells it can take hundreds of cycles for them to go out of balance. Also, he has already said he checks for balance regularly with his set up.

 

[guerney]

One of these ?

View attachment 53666

Thanks, ordered.

There are four calibration outfits near me, and at least one calibration service on ebay. Sending them my cheapo would make them laugh.

Calibration Service Multifunction Tester Megger, Fluke, Metrel, Kewtech, Di-Log | eBay

Find many great new & used options and get the best deals for Calibration Service Multifunction Tester Megger, Fluke, Metrel, Kewtech, Di-Log at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

 

[Woosh]

The logic of an BMS is the charging current will always be higher than the balancing current. It follows from that if you charge your battery until the current is zero, the balancing job is done. Unless you have a BT enabled BMS, you can't reprogram its settings so charging at lower voltage is not practical. Replacing the BMS is the least expensive way to change the maximum voltage.

 

[saneagle]

Because if you start with quality matched cells it can take hundreds of cycles for them to go out of balance. Also, he has already said he checks for balance regularly with his set up.

If that were possible, BMZ and all the other battery makers would save money by removing the balancing function from their batteries. It's there for a reason.

 

[WheezyRider]

If that were possible, BMZ and all the other battery makers would save money by removing the balancing function from their batteries. It's there for a reason.

Early batteries were not made so consistently, so balancing was more of an issue. These days, cells can go hundreds of cycles without going out of balance and I have observed this myself. It doesn't mean the balance function is redundant, it is an insurance policy.

 

[WheezyRider]

in that article by BMZ on the Samsung ICR18650-26F, the benefit of 4.1V charging begins to be noticeable from over 1500 full cycle discharge. Most e-bikers would use much less than 100 full cycles a year, about 5,000 miles a year from a 36V 15AH battery (full cycle discharges are cumulative, one cycle count equals 100% capacity).

Not so sure on the relevance of that plot. This is what Samsung say:


So after just 300 cycles, capacity is down to ~70%. 4.1 V charging would be a lot better than this after only 300 cycles.

However, as I have said previously, unless you are sufficiently technically minded, have the time and patience and care about needing to replace your pack frequently (eg for heavy users), there is no point worrying about trying to charge to 41 V.

Furthermore, this thread is not about charging to 41 V, it's about how someone who wants to check things can gain an insight into how reliable their DVM is without spending lots of money on getting it professionally calibrated.

If you buy an e-bike from a reputable brand, there's a good chance they will have done a reasonable job of ensuring the charger is set to the right voltage. But, what if someone buys a replacement charger, or say a spare charger for work from another supplier or online? I've bought some that were supposed to be 42 V, but were actually over 43 V.

 

[Woosh]

But, what if someone buys a replacement charger, or say a spare charger for work from another supplier or online? I've bought some that were supposed to be 42 V, but were actually over 43 V.

that's a tricky situation.

 

[AntonyC]

Well known brands are a help but haven't always guaranteed quality, so we need to measure.

For a spare charger the OEM one could act as reference for a cheap meter and at the right voltage. My meters aren't linear enough to check with a low voltage reference.

Multimeter guide

Still on topic, if charging voltage were less critical a DVM wouldn't need to be so accurate.

'Full' voltage isn't critical. Weather ensures we can only make a rough estimate of the battery size to buy and round it up, so it's a non-issue to use a few % less of the capacity or compensate with a few % extra Ah and weight. Climbers haul their ropes up mountains and still choose 1.5 tons rating.

With a charger that could be off-spec we can reduce the 'full' voltage on most charges by using a timer, diodes, the battery lights or a cheap DVM. We only need an accurate DVM when the window between balancing and unsafe voltages seems small and we can't rely on the BMS to protect the battery. Lower balance voltage would avoid that, and make batteries safer as WheezyRider explained.

So should we only use trusted chargers? The only defence a cell pack can be sure of is its own BMS, and a trusted charger can drift, develop a fault or be used with the wrong battery. Good chargers can't cover for poor quality BMSs, whereas if the BMS works an over-voltage charger shouldn't be a problem:

battery charging

does ebike charger switch off at full charge or is it the bms that stops the charge , my 36v battery only charges to 35 v not 42

endless-sphere.com

 

[guerney]

All of the battery/fire/charger etc. discussions are very enjoyable and informative, if and however they meander. This @StuartsProjects linked is winging it's way to me now, arriving in a couple of weeks via SpeedPAK:

https://www.ebay.co.uk/itm/195007011445?var=494886040971

...also this for a few Denari more:

https://www.ebay.co.uk/itm/195007011445?var=494886040972

I may yet attempt assembling @WheezyRider's circuit because:

"Man with one watch always knows the time. Man with two watches is never sure."

and

"Man with hole in pocket feel cocky"

 

[guerney]

Yes it's the older version of this and the one I received sets voltage accurately.

RD RD6018 60V 18A DC Adjustable Step Down Stabilized Voltage Lab Variable Bench Power Supply Buck Converter

Smarter Shopping, Better Living! Aliexpress.com

vi.aliexpress.com

Direct Calibration Solutions | UKAS Accredited | ISO9001 Certified

Experience the precision of our UKAS accredited calibration laboratory in the UK. With a focus on accuracy and compliance, our expert team offers comprehensive in-house and onsite calibrations. Trust us to deliver tailored solutions, backed by industry expertise, for all your calibration needs...

www.directcalibrationsolutions.co.uk

Calibration can be pricey but I got quick tests over a narrow range and Chris gave a very fair discount.

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.