On the subject Lewis brings up...
There are a variety of battery charging schemes:
Single Stage, Two Stage, and Three Stage.
The very short version of this:
Single Stage - usually a float charger, low amperage, fixed voltage.
Not intended to supply current to a load. Very slow to recharge
batteries. When used to power a load as well as charge batteries will
usually leave batteries undercharged. May also cause poor equipment
operation when AC is restored after an extended outage as the DC voltage
will rise slowly - this can cause unpredictable operation of attached
network equipment.
Two Stage - High(er) voltage and current to charge battery, float
voltage after fully charging battery. Usually dangerous to your
batteries when also powering a load - the charger can't tell the
difference between the current going into the batteries versus into the
load. The charger always thinks the batteries are still bulk charging
and leaves the voltage too high and will cook the batteries.
Three Stage - Similar to two stage but also includes a boost voltage
above the bulk charge to equalize the voltage in all of the batteries.
Can also cook batteries when trying to supply load current.
Best version - a 3 stage charger with separate current sensing for the
load and battery current, along with temperature monitoring of the
batteries. This allows the charger to know how much current the
batteries are consuming so that it can determine charge state
accurately. Temperature compensation is to adjust the float voltage for
temperature.
Mark
On 4/24/15 9:06 AM, Lewis Bergman wrote:
And as a side note, you should be worried about the opposite issue.
Every supply is built to handle a load all the time. You need a supply
that is designed to both handle a load and float batteries. A standard
PS has a good chance of cooking your batteries if you constant load is
much lower than your PS rating.
On Fri, Apr 24, 2015 at 7:46 AM, Mark Radabaugh <m...@amplex.net
<mailto:m...@amplex.net>> wrote:
DC power supplies rarely care if there is another source of
voltage that the power supply sees on it's input. It is not
unusual for a AC/DC supply to have to power up into an existing
potential. Many DC loads, on a brief power interruption, still
have significant voltage that the power supply is going to see
when AC returns.
* This comment is general and may not apply to every power supply *
From experience the only supply I know that won't deal with power
on the output is one of the larger MeanWell AC/DC 48V supplies.
The internal voltage regulator is too slow to respond and ramps
the voltage up over the high voltage limit and shuts the power
supply down if it's powered up when there is already a battery
voltage on the output. If you power up the supply and then add
the battery it's fine - but not very practical.
Every other AC/DC supply I have tried has worked fine doing what
you are asking to do.
Mark
On 4/24/15 1:34 AM, TJ Trout wrote:
I have a dc load that I need to power using a switching ac to
dc power supply but I also occasionally need to power the load
from batteries, I was planning to put the load, power supply
and battery clamps in parallel, is that a acceptable solution
? Can I power the load from battery and back feed DC into the
supply without damaging it? Would there be a significant drain
back into the supply?
If this isn't ok, what's better solution? Diode ? SPDT switch ?
The load is 50V 100A so that makes diodes and switches a
challenge to find. ..
