On 7/3/2011 8:21 PM, who where wrote:
On Sun, 03 Jul 2011 17:01:06 -0500, brian whatcott
wrote:

On 7/2/2011 11:15 PM, Peter wrote:
On Sat, 02 Jul 2011 14:27:52 -0500, brian whatcott
wrote:

I've got a problem. A good problem.

Always wanted a clamp meter - but never wanted to pay the price.
So when the cheapie Chinese models came along, I bought one.
A model DT3266E to be precise.
2A~ 20A~ 200A~ coupla ohms scales and voltage scales
with attached leads.


Anyway, I knew in my head that cheapie clamp ons are only
good for AC - and that's what the range selecter said too.

But still, I bought a way expensive little lead acid battery for a Honda
Recon 4 wheel RV, and filled it with the acid provided then hooked it to
a charger.

I tried the clip on. It read 2.5 A initially.
That seemed about right.
It tapered to 0.9 A in the next few hours. THAT seemed right.

Here's the problem: if it works on DC ( or maybe rough DC)
why is it marked for AC only?

Brian W

Could be a problem with the iron circuit getting sturated at higher
levels of DC current, even though it seems to work at the lower
levels, and also there may be the problem of magnetising the core, and
causing subsequent measurements to be inaccurate.

peter

Thanks for the sensible suggestions, folks. The clamp is made from
laminations, no doubt.
Just surprised it tracked so well on low DC amps.

Try it on straight DC, such as the main battery leads in your vehicle
with headlights or sidelights only. You may just discover that
Ralph's explanation is correct.

(I have a cheapie battery charger which is nothing more than a
transformer and full-wave bridge, so the waveform of charge current is
a series of pulses at 100 Hz. I have two clampmeters, an AC-only unit
which registers on my cheapie battery charger's output, and a
Hall-effect cheapie which shows DC correctly. Must admit I haven't
tried the HE one on the battery charger yet. Expect a "compromised"
reading or just average current. Note to self ...).


Wandering way off topic - the talk of charging batteries with 'rough' DC
reminds me that some years ago now, it was found that a "two steps
forward, one step back" charging approach is supposed to have a very
healthy effect on batteries. That is to say, a leaky recifier that
discharges at a fraction of the rate that it charges on each half cycle
is supposed to eliminate the formation of spurs and peaks on electrodes
which improves battery life....
(Come to think of it, this 6 amp charger of mine never charges much over
2 amps any more, even when working into a battery with a dead cell)

Brian W