dave hillstrom wrote in
:
On Mon, 25 Jun 2012 19:32:04 -0700, mike wrote:
On 6/25/2012 3:57 PM, wrote:
Hi
In my little world, the plan is to use a 500W modified sine wave
inverter to power a couple chargers that I can't seem to find the
12V equivalent for.
One would be a regular 110V Ryobi charger and the other a 110V
charger for 9 Volt Ni-MH batteries.
After getting this stuff together I read that using an transformer
with a inverter is bad. What would happen? Would I fry something?
Any insight would be appreciated
TIA
Bob
The problem is the dV/dT. The rectifiers and caps are rated for the
current you get when driven with a sine wave. Stresses on those
components can be significantly higher. But maybe they can take it.
So, my experience is that it's perfectly safe to run most anything
from an inverter...EXCEPT when it isn't.
Here's an example.
Tektronix 211 miniscope. Good company. You'd think they designed
good stuff.
They -used- to. the TEK of today is not the TEK of the earlier years.
the 200 series was a good product,very popular with field service
people,especially the 213 with it's DMM.
Plugged on into an inverter and it quit.
Gazing at the schematic showed why. They use a series cap
and rectifier as a charge pump to charge
the batteries. The cap has a different value depending on the
market, 50 or 60 Hz.
The fast rise input waveform from the inverter blew the fuse
instantly. Could have been much worse.
Compaq laptop.
They hooked the battery thru a FET to the input socket. Relied
on the current limit in the adapter to set the charge current.
If you put voltage into the port, it smokes the FET.
But the manual did say, "Use only the recommended charger."
Bottom line is that it's a crap shoot. For most consumer devices,
vendors are more concerned about saving half a cent than whether it
works in an environment not in their spec. Clever implementations
that save cost don't necessarily enhance reliability.
to follow up on this, if the battery charger is using a cheap
cap-based power circuit to produce consant current for fast (15 min to
1 hour) nicd and nimh charging, you may very well get flames and smoke
coming out of your charger and/or batteries if used with a poor
modified sine wave output from a generator.
the TEK 211(and 212,214,and 221) is not a fast charger circuit.
in fact,TEK had to add a protection circuit and fuse the individual battery
packs to keep the scope from catching fire,literally.
One other item to watch out for on the TEK 200 series is that the PCBs are
held in place by 4 plastic pins,two on each case half. they shear off under
impacts,then the PCBs shift in relation to each other,the female pin
connectors spread open and their spring leaves fall out,shorting things
out.
--
Jim Yanik
jyanik
at
localnet
dot com