Put DMM current metering into charge/discharge circuit next to cylindrical cell (-s)

Oiyuk Ti

Newly Enlightened
Joined
Apr 27, 2020
Messages
19
Put DMM current meter in series to charge/discharge circuit next to cylindrical cell (-s).

I wonder if ready to buy piece of hardware is available in the market to put DMM current metering in series next to cylindrical cell (-s) while these are charged (in charger) or discharged (in device, in charger) - kind of DMM accessories, probes. Could be built from small piece of double-side copper board with one pin on each side for DMM probe connection, enough distance copper-free on board edges for free of short-circuit usage. Piece of copper board sufficiently thick according to level of current measured.
Adequately an accessory to connect DMM voltage meter to cylindrical cell while it is being charged or discharged (in device).
I working on multiple technical questions for household and hobby and won't be able to build every missing component by myself therefore my preference is to order.
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
11,212
Location
Tulsa,OK
You can easily put a DMM in series with a battery charging circuit you just need 2 very thin pieces of metal with an insulator between them (tape works or thin plastic) to slide between the charger contact and battery and hook up a DMM in ammeter mode. Depending on how much current you want to use I would opt for the high amp separate circuit on many DMM usually 10A or so as the shunt used to measure it through will give you less loss as it is lower resistance.
The problem with doing this however is it will affect the charging itself as it adds into the battery circuit more resistance which will throw off any readings the charger has on it (if it has a digital meter built in). One other thing that also can be done if you don't have a meter with an amps scale is to take a low value resistor like 0.1ohm and put it in series with the charger circuit and measure across it to find the voltage drop and using ohms law you can calculate the current flowing through it.
 

bmengineer

Newly Enlightened
Joined
Jan 26, 2018
Messages
142
Location
Ontario, Canada
I use a sticky note with copper tape on each side, and clip the DMM leads to that. Works great, but adds a fair bit of resistance to the circuit.
 

DIWdiver

Flashlight Enthusiast
Joined
Jan 27, 2010
Messages
2,725
Location
Connecticut, USA
How about using the nickel strips they use for building battery packs?

Or even better, I found these nickel plated copper strips on ebay. These are better because copper has about 4x the conductivity of nickel, and also these are thicker than most of the nickel strips, and nearly 10x thicker than the standard 1 oz. copper on a circuit board. Yes, I know you can get thicker copper on circuit boards, but even 2 oz costs more, and more than 3 oz gets really specialized.

https://www.ebay.com/itm/Pure-Nicke...hash=item1efdab9a07:m:mMtwhK3c5GCJ22oWz3WzgHA
 

DIWdiver

Flashlight Enthusiast
Joined
Jan 27, 2010
Messages
2,725
Location
Connecticut, USA
Hang on, two traces 1" (25mm) long and 0.3" (8mm) wide on a PCB with 1 oz. copper would have a combined resistance of 0.00001 ohms. They would be getting barely warm at 10A, and quite warm at 20A. I'm starting to think the OP's idea isn't that bad after all.

I could design and order a board like this in an evening. It could have spots to solder on the surface mount or through-hole resistor of your choice, as well as to solder in wires to go to a meter, or even meter probe jacks. From China you could probably get one for $0.99 and free shipping, assembled. From me you could probably get a bare board for a few times that plus shipping. Would CPFers be interested in this? For lowest cost, the board would have to be 0.062" (1.6mm) thick. Thinner would at least double the price (from me), probably even more.
 

Lynx_Arc

Flashaholic
Joined
Oct 1, 2004
Messages
11,212
Location
Tulsa,OK
I actually have a double sided circuit board with a push button switch on it I got out of an Energizer light that used it to "try it" that I slide inbetween a battery and contact and connect my meter across the button part.
 

Oiyuk Ti

Newly Enlightened
Joined
Apr 27, 2020
Messages
19
@DIWdiver
Please accept my apologize for coming this late, I didn't realize few further updates were made, including yours, hadn't this thread subscribed damn.
Thank you also for your offer which is interesting, however I will need some time to work on my order setup, also to get familiarized with all details your message.

For me following, at least, these questions are open:
The minimum thickness of copper board to support max charge currents of MC3000, SKYRC, any rechargeable types supported by this charger.
The minimum thickness of copper board to support max discharge currents against all my current rechargeables.
Same questions possibly concerning copper paths too.
Copper oxidation effect - boards will possibly need occasional cleaning.

My order setup will probably include:
amount: 2 pairs - just in order I lose one certain day
additional boards pair with board length appropriate for D size
bare boards should be no problem
however each copper path edge 0.08'' - or so - away from board edge

I didn't get the point with soldering points for resistor, sorry. Do you eventually mean indirect current measurement through voltage measurement ?
 
Last edited:

bmengineer

Newly Enlightened
Joined
Jan 26, 2018
Messages
142
Location
Ontario, Canada
Hang on, two traces 1" (25mm) long and 0.3" (8mm) wide on a PCB with 1 oz. copper would have a combined resistance of 0.00001 ohms. They would be getting barely warm at 10A, and quite warm at 20A. I'm starting to think the OP's idea isn't that bad after all.

I could design and order a board like this in an evening. It could have spots to solder on the surface mount or through-hole resistor of your choice, as well as to solder in wires to go to a meter, or even meter probe jacks. From China you could probably get one for $0.99 and free shipping, assembled. From me you could probably get a bare board for a few times that plus shipping. Would CPFers be interested in this? For lowest cost, the board would have to be 0.062" (1.6mm) thick. Thinner would at least double the price (from me), probably even more.
I'd buy this, especially if it included a resistor - low resistance ones can be difficult to source
 

DIWdiver

Flashlight Enthusiast
Joined
Jan 27, 2010
Messages
2,725
Location
Connecticut, USA
No problem coming in late. I know people come and go, and don't always read every thread every day.

Surface mount resistors down to 1 milliohm and below are in stock at DigiKey, for same-day shipment. They are a little more expensive than more common values, but not unreasonable.

Is there any reason to think that currents above 15A would be needed? That would be supported by the 1-oz copper that's available on the super-cheap board specials. That way parts cost (including resistor) could be under $2 per board. Shipping to me would be $45-50 for the lot, which would have to be amortized across however many boards would get sold. Shipping to you would be whatever a USPS padded envelope costs from the US to your location.
 

Latest posts

Top