Multimeter guidance

dewaltdisney · Post by **dewaltdisney** » Sun Sep 08, 2024 4:07 pm

I wanted to check the voltage in my 21v Lithium Ion batteries. Am I safe to set the MM to 20v and touch the probes on the and - contacts on the battery to see what voltage they hold. As you all know I am not great with electrics.

DWD

Someone-Else · Post by **Someone-Else** » Sun Sep 08, 2024 4:33 pm

NO! When checking for voltage, the meter should always be set HIGHER than the expected voltage, this will prevent the smoke from being released. As it is a battery you are testing, the meter should be set to D.C. (Sorry if you knew that)
Also, voltage is the difference between two points, it does not tell you if the battery (in this case) is good, but it will indicate if it's (Insert your own adjective here) or not.

dewaltdisney · Post by **dewaltdisney** » Sun Sep 08, 2024 5:24 pm

Thanks for that SE. You made me realise that it is high time I watched a basic tutorial on using a MM. I now have a better idea for the settings rather than blindly going about it by guesswork. I will let you know how I get on.

DWD

OnlyMe · Post by **OnlyMe** » Sun Sep 08, 2024 5:33 pm

Someone-Else wrote: ↑Sun Sep 08, 2024 4:33 pm NO! When checking for voltage, the meter should always be set HIGHER than the expected voltage, this will prevent the smoke from being released.

What a load of rubbish. Do you actually know how a voltmeter (digital or analogue) works?

dewaltdisney · Post by **dewaltdisney** » Mon Sep 09, 2024 11:05 am

After my YT tutorial I got a better idea on basic MM use and I tested my batteries using Stanley blades in the terminals. Both showed 20.8 volts so I am a bit perplexed.

DWD

wine~o · Post by **wine~o** » Wed Sep 11, 2024 11:40 am

Why perplexed ? what were you expecting ?

dewaltdisney · Post by **dewaltdisney** » Wed Sep 11, 2024 12:16 pm

One was duff in the saw, that was what was perplexing especially as it was showing 20.8 volts. The others from my previous saw also did not work but also showed 20.8v. I hot-wired a good battery from the new saw onto the old saw and it works.

DWD

wine~o · Post by **wine~o** » Wed Sep 11, 2024 4:56 pm

Volts arn't always a reliable indication of the state of the battery, sometimes the internal resistance of one or more cells can go high. Can't be measured by a multi-meter.

dewaltdisney · Post by **dewaltdisney** » Wed Sep 11, 2024 5:14 pm

So what you are saying is that the batteries are buggered. A skilled person could check each cell and replace the defective one but it is hardly worth it for a £20 tool. I am loathe to spend out again as I may well get more shite batteries. I have one saw that works for about an hour with the only good battery.

DWD

ericmark · Post by **ericmark** » Wed Sep 11, 2024 11:15 pm

Most batteries today have a tester built in, those which have not, normally it is also built into the charger. It can be a bit of hit and miss, I have three batteries for my camera, and one does seem to have a life of its own, some times it will charge and some times it will not, the problem is the battery has electronics inside it, and this varies battery to battery, so open circuit voltage can be misleading.

The Lidi battery instructions show the voltage

: Lidi battery.jpg (57.4 KiB) Viewed 292 times

and as you can see you can easy test if full or empty, but the voltage between to two extremes does not vary very much.

My saw needs two batteries, I have four, and my charger will charge two batteries at the same time, I note my 16 volt drill shows 15.58 volt the 20 volt batteries I do not have to hand, but the point is empty to fully charged not that much change in voltage, house battery shows 51.2 volt and 10% charged, seem to remember fully charged is around 54 volt so there is a built in computer which logs the charge and discharge, same applies with a laptop.

Now if using lead acid then it would be very different, but the lithium battery is not that easy to work out what power is left.

dewaltdisney · Post by **dewaltdisney** » Thu Sep 12, 2024 5:45 am

Thanks for that Eric, I think the issue is that these are cheap Chinese batteries and the quality control is probably poor. I noted when I took a battery case off that there is a PCB type board which I suspect might be the culprit. The chargers with these batteries have a red light when charging and a green light when it is charged. The duff batteries all show green, and have 20.8v, but they do not work. As I have said when you pay £20 for the whole kit you have to expect a problem and I have written this kit off on the work I did get out of them as they both did a fair bit of work albeit a short life. I will write it off to experience as I am at the end of my cutting season now.

DWD

ericmark · Post by **ericmark** » Thu Sep 12, 2024 10:50 am

I was looking today at voltages on my main battery, as said was 51.2 volt and 10% charged last night, today 80% charged at 54.1 volts, being charged at 683 watt. I went down stairs and removed a fully charged battery off the fast charger, it has been charged now for around a week, and it shows 20.77 volt.

While writing this, main battery up to 88% and showed 55 volt charging at around 2 kW, wife just gone to have a shower and voltage dropped to 53.7 yet not showing any discharge. Dropped to 81% discharge 3 kW and shows 51.6 volts, so it seems volts does not tell one much about battery state.

After shower completed the battery down to 52.8% but the battery voltage has lifted to 52.8 volt, charging at 852 watt. Clearly with an appliance battery you can't measure as the load or charge rate alters, this can only be done due to the solar power software.

ericmark · Post by **ericmark** » Thu Sep 12, 2024 12:29 pm

P.S. at 100% showed 54.4 volts on my main battery. Rated voltage 51.2 volt. range 43.2 to 57.6 volt, not seen it get near that.