# diode question



## Ziggythewiz (May 16, 2010)

What do you mean by "ac dc shorepower" ? Is it a DC power supply that's plugged into the AC mains?

And where does the "dc dc" (unless it's a DC-DC converter you only need to say DC once) power come from?


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## frodus (Apr 12, 2008)

As always, Draw it out. MS paint, and the post it on here.


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## evmetro (Apr 9, 2012)

Yes, the ac dc is my 12 volt power supply that is wired into my ac mains. The dc dc 12 volt power is my aux battery and dc dc converter system that supplys power through my ignition switch. My 5 pin relay switches the dc source for my cooling pump.


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## frodus (Apr 12, 2008)

frodus said:


> Draw it out.


Get used to this, as you do more conversions, and ask more, you're going to have to post some schematics. 

It's very difficult to try to understand what you're saying verbally. Draw it out.


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## Ziggythewiz (May 16, 2010)

So you're really trying to connect a 12V DC power supply to a 12V DC battery?


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## TEV (Nov 25, 2011)

What ever that " cooling pump " is, he want to switch it from the auxiliary battery power, to a 12v power supply when parked.
Indeed he has to specify if the auxiliary battery will be connected to the 12v power supply for charging or not.


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## evmetro (Apr 9, 2012)

Ok, looks like I gave too much info. What diodes would one use to isolate a 12v aux battery from an ac powered dc 12v power supply if their positive leads were to touch each other? Is it necessary to isolate these two? The grounds are not isolated.


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## Ziggythewiz (May 16, 2010)

First of all, there's no such thing as too much info, especially since everyone responding has asked for additional info.

To answer your question: Typically None. That's how a battery charger works. If you isolated them they wouldn't be touching. 

The only issue is that if this is a power supply and not a charger, is it properly matched to the battery? If the battery is a higher voltage than the power supply it could try to charge the power supply (which may or may not be a problem), which you could prevent with a diode, but if that were the case why would you be plugging them together anyway?


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## frodus (Apr 12, 2008)

Why wouldn't you just have the DC-DC on while it's plugged into mains? The AC supply you've got seems redundant if you have a DC-DC converter.

Is this in any way wired to the Orion?


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## skooler (Mar 26, 2011)

frodus said:


> Why wouldn't you just have the DC-DC on while it's plugged into mains? The AC supply you've got seems redundant if you have a DC-DC converter.
> 
> Is this in any way wired to the Orion?


+1 for the above


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## tomofreno (Mar 3, 2009)

evmetro said:


> ...but I immediately thought of this forum.


 Bet you will think again next time!
I'm not sure what you want to do, but if you want to ensure only one 12V source is connected at a time a DPDT (double pole double throw) relay activated by the ignition would do it.


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## evmetro (Apr 9, 2012)

I have an ac dc power supply to provide a charge power signal to the orion, and it is convenient to use this since the ac dc power supply is located with the ac main contactors, and all the charging related relays. My cooling pump for my controller and liquid cooled pfc 40 should be able to run when the orion is providing the charge enable signal, and when I am driving down the road so I have set up a relay to switch the source of the dc positives, based on if I am plugged in and charging, or if I am driving it. When the key is off and there is no shore power plugged in, the pump relay receives no signal. Turn the key on and it sends 12 volts to the nc circuit of the relay and the relay does not have to do anything. Plug in shorepower and the ac dc power supply activates the pump relay coil, switching power source to the ac dc power supply. Since starting this thread, I have re examined the relay circuit and determined that since the pin that supplies power to the pump is the pivit pin in the relay, that there will be no way for the two power sources to connect. I am sure that I will have to get educated in diodes at some point very soon with all the conversions that I have going and have planned, but for my this pump circuit I think I will get by without having to take that class. (yes, that class is a day of wiki, google and dumb questions here) I hope at some point I can translate electrical engineer language to the layman. There seems to be a pretty big language gap between the two, and my perception of this site, based on the name is that there are a lot more layman types in a "diy" environment. The extremely educated are the few, and probably somewhat burdened by the number of "simple questions" that come up. The engineers are a critical source of information here, and I hope to be able to carry some of the burden soon.


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## frodus (Apr 12, 2008)

Why is it so hard to sketch a schematic?

That would help with 90% or more of your questions (from what I've seen you post on this forum).


IMHO, a decent build will go much smoother with a laid out sketch of the entire system.


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## evmetro (Apr 9, 2012)

I actually sketch a lot of them as I plot circuits, but I have trouble posting them. I use my droid almost exclusively, and for me to post pics, I need to use the sit down in front of it style computer. Other family members are usually sitting in front of it or I am at my conversion shop where I am building all these EVs.


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## frodus (Apr 12, 2008)

Connect the android to the comp, go to DCIM and find the pic, and post them... if you need help, I don't mind, but it's difficult to understand how things are phsyically wired when there's only a text explanation.... which as you can see, has been misunderstood.

Another option is to get email connected on the droid, attach the pic to an email, and mail it to yourself. Then log into email on the computer, get the picture, save it and then post it.


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## evmetro (Apr 9, 2012)

I am just coming up to the point where I can plot an entire ev on a schematic, but in the beginning I was having to spend a lot of time drawing up individual circuits and the learning curve was steep but most of those I have mastered now. The schematic that you had me draw up on "the metro"in build thread is now obsolete, but was an extremely valuable drill. It felt like the teachings in the movie "karate kid". I was a little disgusted to have to go through all that, but I learned quite a bit. I have a couple more builds in the works, and I do plan to draw the schematics from the get go. One is basically a replica of "the metro" with a few small variations and the other is upgrading my lead sled metro to lithium.


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