Question about combining power supplies....

[Jacktal]

I work in heavy machineries where we often have two or more batteries linked either in parallel or in series depending on the machine's needs.Parallel wiring gives battery amperage X number of batteries while series wiring gives battery voltage X number of batteries.

What I'm curious to know is if one could do the same with DC power supplies.Could we take two PS of equal voltage and link them in parallel to obtain their total wattage capabilities like if they were batteries or would one have two PS that would fight eachother to destruction and even become a fire hazard.And would result be the same if the PS were of different wattage,given the voltage is the same.

[Johnnny_reb]

NO. It would be unsafe to do.

[jeffrey-wimberly]

Absolutely not! My nephew tried that once and almost burned the house down. What works well with batteries does not work with a model train power pack.

[jrbernier]

  I assume you are talking about DC power packs?  I would not hook them up in series - there is a potential for a lot more voltage to the engine than it can handle!  In parallel, you have the problem of two throttles and a reversing switch to manipulate at the same time. 

  What are you trying to make happen here?  Most good power packs can handle 2-3 engines in a consist at the same time.  I can see using the fixed outputs of 2 identical power packs as a 'power source' that feed a seperate throttle - if you want to increase the available current for heavy loads.

  With DCC, you can just add another 'booster' ...

 

Jim Bernier

[Mark R.]

Actually it CAN be done, but there are some very critical measurements required and some very extensive mathematical equasions to be calculated - not to mention some very exacting knowledge of the specs of each supply in order to do this.

A transformer works on the principal of inductance between the input and output of the transformer. In order to parallel two inductance transformers, you need to know specifics like the exact number of primary / secondary windings, guage of the wire, etc. There is also a "floating current" created when one or the other transformer is conducting - if the balance point exceeds a calculated thesh-hold, it is certain disaster (melt-down / fire). Parallelling inductance transformers is an exacting science.

So - In a shorter answer .... no, don't "try this at home" !!!

Mark. 

 

[gandydancer19]

I agree.  It can be done if you are working in the electronics industry and know how.  Otherwise - "don't try this at home".

[Jacktal]

Thanks.This is what I had suspicion about and wasn't going to risk ruining good power supplies to test this,not mentionin the fire hazard.But I was curious if it was possible,at least in theory.By the way,I meant fixed voltage DC power supplies with constant polarity.

[MisterBeasley]

I heartily agree that it's not a good idea.

Instead, think about dividing the load.  Use one supply for turnouts, and another for structure lights, streetlights and signals.

[larak]

Could we take two PS of equal voltage and link them in parallel to obtain their total wattage capabilities...

If they are EXACTLY the same voltage you can do it. Real world supplies will not have identical output voltages. However if you feed the output of each through separate isolating diodes you can run them in parallel thus increasing the total wattage (current) available. The voltages still have to be pretty close. If you're really paranoid add a small ohm-age resistor in series with each, perhaps 0.1 ohms at one watt. 

Note: the ouput currents will not be identical, just close.   Do not expect two 1 amp supplies to give you 2 amps. Larger series resistors = better load sharing but more wasted voltage across the resistors.

Also, I would not do this with unregulated wall warts, but it works just fine with commercial grade power supplies.

 

 

[jbinkley60]

I work in heavy machineries where we often have two or more batteries linked either in parallel or in series depending on the machine's needs.Parallel wiring gives battery amperage X number of batteries while series wiring gives battery voltage X number of batteries.

What I'm curious to know is if one could do the same with DC power supplies.Could we take two PS of equal voltage and link them in parallel to obtain their total wattage capabilities like if they were batteries or would one have two PS that would fight eachother to destruction and even become a fire hazard.And would result be the same if the PS were of different wattage,given the voltage is the same.

Placing them in series is not dangerous and as long as you get the polarity right you'll end up with an output that is the sum of the two voltages.  Get the polarity wrong and you'll get the difference of the two output voltages. 

Now placing them in parallel is another matter and the "don't do this at home" recommendation is probably best.  However, why not just split the load and fed part of the load from one power supply and the rest of the load from the other.  As long as they are connected together this will work fine.  I do this for building lighting.  I run multiple lighting buses, each with its own properly sized power supply.  Now if you are trying to drive a single loadm this obviously won't work.