question regarding digital multimeter

[Solarfun4jim]

Just started my first ever top balance of a battery bank...nerves jangling a bit....lol (8x280ah in parallel)
Is there any harm in leaving a digital multimeter connected across the pack for hours at a time?
Also, i noticed that after having set my bench top power supply to 3.63v it has crept up to 3.67v over the period of half a hour....i take it this is normal as temperatures change etc? I had thought that it would hold at 3.63v exact? I presume this is my total inexperience showing

 

[gnubie]

No harm at all. The average digital multimeter places essentially no load in voltage mode but even an old non-FET based analogue meter draws piddly power to keep the needle pointed.

A quality bench meter will have close to 0 temperature drift. A cheapie will drift, it's the nature of these things. Is your meter a quality item or a cheap thing from ebay etc? Make and model would let people advise you if the voltage drift is normal for it.

 

[HRTKD]

Where are you seeing the 3.67 reading? On the power supply or on the digital meter?

Make sure your power supply didn't switch to Constant Current. I bumped mine and did just that. I set the volts again and it was fine after that.

 

[Solarfun4jim]

No harm at all. The average digital multimeter places essentially no load in voltage mode but even an old non-FET based analogue meter draws piddly power to keep the needle pointed.

A quality bench meter will have close to 0 temperature drift. A cheapie will drift, it's the nature of these things. Is your meter a quality item or a cheap thing from ebay etc? Make and model would let people advise you if the voltage drift is normal for it.

Thanks gnubie...both the bench top suppy and meter are cheapies im afraid. Bench top supply is a longwei 3010DF, meter is a DT-830B.....before you groan, yes both chinese units....blew a hole in my budget by buying a liteon cobbled together unit that turned out to be useless for the job at hand.
The bench top drifts up to 3.67v then back down again to 3.65v. I'm presuming this is still perfectly usable.

 

[Solarfun4jim]

Where are you seeing the 3.67 reading? On the power supply or on the digital meter?

Make sure your power supply didn't switch to Constant Current. I bumped mine and did just that. I set the volts again and it was fine after that.

Thanks, on the power supply. Digital meter is reading 3.35 across the terminals. C.V .led is still lit.

 

[HRTKD]

Should be OK then. Test each battery at the terminals, not the bus bars. I made the mistake of testing at the bus bars, just to find that I had two bad connections.

 

[Solarfun4jim]

Should be OK then. Test each battery at the terminals, not the bus bars. I made the mistake of testing at the bus bars, just to find that I had two bad connections.

Thanks. Just checked across every battery cell...they are all 3.36v
I tweaked the psu back just a fraction and now it is displaying between 3.63-3.64v, so appears to be more stable now???

 

[HRTKD]

As I recall, mine varied a bit and that got me concerned. Eventually, it got to the right point. I did do it in two segments because I was paranoid. Up to 3.60 and then to 3.65.

 

[Solarfun4jim]

As I recall, mine varied a bit and that got me concerned. Eventually, it got to the right point. I did do it in two segments because I was paranoid. Up to 3.60 and then to 3.65.

Yes, i had thought of doing a three step charge to 3.4, then 3.5 then 3.65, but at the amps being put in, i was told by another poster that the pack would be overcharged long before getting to 3.65v
On a 280ah cell, you need to be putting in over 14A so that you can see the current tail off (0.05C for eve cells is called quits on the C.C. phase.) Unfortunately, with only putting in approx 5.5A , i'm not going to see the tail off current(as far as i know) before an overcharge condition presents itself. Thus i opted to go straight for 3.65 with a view to immediate termination when it gets there.

 

[Solarfun4jim]

I'm assuming there is no negative effect, disconnecting the power supply at night and resuming in the morning again, so i can keep an eye on things....guess i'm more paranoid than most when it comes to electricity and safety.

 

[HRTKD]

Many members have stopped the charge at night. No problem.