Hi.

I managed to salvage a small -48vdc power system which I'm planning to install at some point. At this point, I would need to test this system and I was wondering could I use incandescent lamps of some wattage as dummy load to test the system? I live in 230v area so incandescent lamps I have are of that voltage.

-48VDC would be POE or phone network equipment

If you just connect it with the GLS in series, guess how much voltage the equipment will get ? Depends on its momentary activity, so basically any momentary value between the rectified line voltage peak to 0V

If you want to add some Zener, think the power dissipation......

There really is a reason why we power things with proper PSUs and not voltage dividers

I was trying to find something I can use as dummy load to test what shape that power system is. So I would need something that would act as load in 48v dc preferable as atleast 150w load

Oh, so it is not about dropping 230V to 48V. I understand now

How about a 230V space heater ? (something that does not have a fan in it, cause the fan won't work with 48VDC and can be fried by the DC)

I was trying to find something I can use as dummy load to test what shape that power system is. So I would need something that would act as load in 48v dc preferable as atleast 150w load

You're going to need a 180000 Watt lamp to do that, unless you have multiple lamps in parallel.

How you got to this figure ?

Assuming constant resistance, 150 * (230 / 48)^2 = approximately = 150 * 25 = approximately = 4000W 230V load

Incandescent is no constant resistance, so it takes lower rated wattage 230V GLS to impose 150W load at 48V

1. 48/150 = .32 Ohms
2. 240/.32 = 750 Amps
3. 240 X 750 = 180000 Watts

Volt / Curr = Res

Multiply it and divide it by Volt :
Volt / Volt * Volt / Curr = Res

Reorder...
( Volt * Volt ) / ( Volt * Curr ) = Res

Volt^2 / Pwr = Res

So its Volt^2 / Pwr = Res, not Volt / Pwr = Res

I don't have any space heaters I could use for that. Since it would only be just a kind of burn in test I was planning to not to have buy anything and since I have lot's of not-in-collection incandescent lamp I just though maybe I could use those as load. But all those equations made me confused so is there are wattage/combination I coul use? Load could be bigger than 150w so that would not be a problem (all the way up to 900w is available)


If this power system is well enought condition I wad planning to buy a small Ah batteries to it and use it not only to my it equiptments but also build some sort of backup lights for blackouts

Other option is 4 identical 12V lamps in series, but they need to really be identical so that one does not start faster than the others and burn up. You can use more lamps and underdrive them

4x 12V 50W Halogens would be a 200W load at 48V

There are many things that can act as resistor while not as well defined one, like bucket of salt Water, Soil between 2 buried electrodes, or various Steel or Iron elements of big size. Things to keep in mind are the power dissipation, which can be uneven but concentrated near connections to the "resistor" medium, and the heat resulting from the high power density near there

If it was mine then I would just get some car headlamp bulbs in series/parralel combination will be a perfect test it doesn't matter if its not exactly 150 watts as long as its nearish! just load it to its rated output leave it for say an hour and if nothings over hot or smoky then your good to go!

Yes, why didn't I think of that. car headlight lamps are probably the easiest solution for this test. I should have some of those laying somewhere. Better dig them out.

There you are then sorted just don't put all bulbs on at once the inrush current will be a bit high and mite make the PSU shut down

4 identical headlight lamps in series are the ~200W 48V load. Its in series. How can he not power them all at once ?

I thought that he would have 2 separate strings of lamps not just one so OK if its only one then fine the inrush won't be an issue