I saw an ad recently from someone offering a redundant input DC power device using MOSFETs rather than diodes for almost zero voltage drop. I think it was ICT.
http://www.ict-power.com/products/display_isolationmodule.php?id=1408 From: Chuck McCown Sent: Friday, April 24, 2015 10:48 AM To: af@afmug.com Subject: Re: [AFMUG] Power supply back feed loss? Generally. Some power supplies will slowly drain your battery when off. Most don’t. You would want to verify with an ammeter. From: TJ Trout Sent: Friday, April 24, 2015 9:46 AM To: af@afmug.com Subject: Re: [AFMUG] Power supply back feed loss? Sorry this was completely wisp unrelated, I only plan on connecting the batteries once and awhile and don't need them to be floated, etc. So I'm guessing it's safe to parallel a power supply and a battery when the power supply is turned off? On Fri, Apr 24, 2015 at 6:20 AM, Mark Radabaugh <m...@amplex.net> wrote: 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> 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. ..
