# Combine 2 power of units to equal 1?

#### Zaam

Apr 19, 2016
1
Can I combine two 300ma power sources to charge my 600ma portable battery jumper?​

#### Harald Kapp

##### Moderator
Moderator
Nov 17, 2011
13,176
Welcome to EP.

It depends on the power sources. In theory two voltage sources of the same rated output voltage can be operated in parallel and deliver an output current that is equal to the sum of the individual output currents. In practice no two voltage sources have identical output voltages. They will differ, even if only by a few millivolts. This has the effect that the voltage source with the higher voltage will deliver power into (!) the voltage source with the lower output voltage instead of the load.
Typically this is resolved by adding balancing resistors in series with each power source. The voltage drop across the balancing resistors will avoid reverse power into the power source with the slightly lower voltage - at the cost of power dissipated in the form of thermal energy (heat).
Depending on the type or construction of your power source the load balancing resistors may not be required if the power source has a hiogh enough internal output resistance. Every power source has such an internal resistance (not in the form of a discrete resistor) which limits the max. output current of the source. An electronically regulated powr source's output resistance is very low (that's what the regulation is for), therefore electronically stabilized power supplies are not suitable for operating in parallel without additional measures.
Batteries on the other hand have a comparatively high internal resistance (due to the limited rate of currrent generation by the electrochemical processes within the battery), therefore paralleling batteries is often no problem.

#### Colin Mitchell

Aug 31, 2014
1,416
Connect them together and put a red LED between the two positive leads. Reverse the LED. If it glows, you definitely CANNOT

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