Two power supplies in parallel - what would the resultant power, voltage & current be

hannahnatasha

I am working with RTGs right now. I want to hook two of them up in parallel to charge a battery. Basically, the setup I had planned is like this:

I am trying to determine the power, current and voltage that would be given to the battery.
I have been trying to research and know about Kirkhoff's laws. However, do they work in this situation when the RTGs have their own voltage and current?

For reference, the RTGs both have a current of 0.248A and a voltage of 13.89V.

How do I calculate what is given to the battery?

Thanks!

Simon Bridge

Yeah - kirkoffs laws work for this situation ... one loop has two PSUs in it and the battery is a load ... you'd normally model the real components as an ideal source with a series load. A totally dead battery starts out as a load and gradually becomes a source as it charges.

I_am_learning

Learned about RTGs for the first time. Wow,they are amazing. In your case, they produce roughly 13.89*0.248 = 3.44 watts each, supposedly for decades.
Just curious, would you mind telling how much does those thing cost?
As for your question, If everything is straight forward, the current given to the battery would be twice.
What is the AH rating of your battery?

skeptic2

I assume the current is short circuit current which implies an internal resistance of 56 ohms. This means that as the battery becomes charged, it will continue to charge slower and slower. If the internal resistance is a constant the formula would look like this.

charging current = (Vrtg - Vbatt) / 56

For 2 RTGs the current would be approximately double.

*Studiot*

Considering the nature of the sources you should not use your simple parallel connection, without proper control and sharing circuitry.

Kholdstare

Check the charge capacity of your battery. Like how much Ampere-hour it can hold. The battery will probably behave like a capacitor being charged, with some internal resistance.

berkeman

And for those of us who had no idea what an RTG is before reading this thread:

http://en.wikipedia.org/wiki/Radiois...tric_generator

.

altos67

You may want to consider putting a diode in series with each RTG. If you connect two sources in parallel, it is likely that one will drive the other and a lot of heat would dissipate in
the wires.

skeptic2

hannahnatasha, If you wouldn't be breaking any confidentiality agreements, it would be interesting to hear more about your project. For what will the RTG be used e.g. space mission, remote sensing, etc.? What isotope are you using for fuel? How hot will the fuel get?

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Simon Bridge Recognitions: Homework Help	Yeah - kirkoffs laws work for this situation ... one loop has two PSUs in it and the battery is a load ... you'd normally model the real components as an ideal source with a series load. A totally dead battery starts out as a load and gradually becomes a source as it charges.

I_am_learning Recognitions: Gold Member	Learned about RTGs for the first time. Wow,they are amazing. In your case, they produce roughly 13.89*0.248 = 3.44 watts each, supposedly for decades. Just curious, would you mind telling how much does those thing cost? As for your question, If everything is straight forward, the current given to the battery would be twice. What is the AH rating of your battery?

Studiot	Considering the nature of the sources you should not use your simple parallel connection, without proper control and sharing circuitry.

Kholdstare	Check the charge capacity of your battery. Like how much Ampere-hour it can hold. The battery will probably behave like a capacitor being charged, with some internal resistance.

berkeman Mentor	And for those of us who had no idea what an RTG is before reading this thread: http://en.wikipedia.org/wiki/Radiois...tric_generator .

altos67	You may want to consider putting a diode in series with each RTG. If you connect two sources in parallel, it is likely that one will drive the other and a lot of heat would dissipate in the wires.

skeptic2	hannahnatasha, If you wouldn't be breaking any confidentiality agreements, it would be interesting to hear more about your project. For what will the RTG be used e.g. space mission, remote sensing, etc.? What isotope are you using for fuel? How hot will the fuel get?