power supply for Hess trucks

[scorp]

Searching the internet for days but have not came up with a solution:

Been looking for a way to power a couple Hess trucks as part of my Xmas display. I have a Radio Shack 12 volt dc regulated 2 amp power supply. I tried using a 7805 regulated 5 volt but it trips the breaker on the 12 volt supply! I don't understand why. I've built circuits from scmatics and kits (just finished the bulbdial clock), but I don't know enough to design one myself. Trucks uses 2 C btw. Any help is greatly appreciated.

Thanks

 

[CDRIVE]

I tried using a 7805 regulated 5 volt but it trips the breaker on the 12 volt supply! I don't understand why. Trucks uses 2 C btw.
Thanks

If your truck uses 2 C batteries then the lighting system is 3V not 5V. You should be using an adjustable regulator like the LM317.

Also, are you saying that your 12V supply trips the breaker by merely powering the 7805? Restated: Is your 7805 output connected to the truck?

Chris

 

[scorp]

If your truck uses 2 C batteries then the lighting system is 3V not 5V. You should be using an adjustable regulator like the LM317.

Also, are you saying that your 12V supply trips the breaker by merely powering the 7805? Restated: Is your 7805 output connected to the truck?

Chris

Yes when powering the truck it trips the 2 amp breaker on the 12 volt supply. In less than a minute.
Thanks

 

[scorp]

just to clarify:
12 volt s supply to 7805 to Hess truck = triped breaker on 12 volt supply.

I used the 5 volt because I didn't think the extra 2 volts would matter since we're dealing with incandescent mini bulbs.

 

[CDRIVE]

Yes when powering the truck it trips the 2 amp breaker on the 12 volt supply. In less than a minute.
Thanks

just to clarify:
12 volt s supply to 7805 to Hess truck = triped breaker on 12 volt supply.

I used the 5 volt because I didn't think the extra 2 volts would matter since we're dealing with incandescent mini bulbs.

That equates to 1.66 * over voltage. Another 340mV would be 2 times overvoltage! The fact that the truck uses C cells indicates that those lamps draw a healthy current @ 3V.
It's likely that those lamps are drawing ~2A @ 5V.

Chris

 

[OLIVE2222]

Hi,

If you can borrow a PC ATX power supply somewhere you will get a very healthy 3V3 power bus .

Olivier

 

[scorp]

That equates to 1.66 * over voltage. Another 340mV would be 2 times overvoltage! The fact that the truck uses C cells indicates that those lamps draw a healthy current @ 3V.
It's likely that those lamps are drawing ~2A @ 5V.

Chris

Thanks for the info Chris. At least I'm learning. So even if I used an adjustable set at 3 volts it would still draw more than the 2 amps that the power supply can deliver?

Thanks again

 

[CDRIVE]

Thanks for the info Chris. At least I'm learning. So even if I used an adjustable set at 3 volts it would still draw more than the 2 amps that the power supply can deliver?

Thanks again

No, we don't know that. I said that those lamps are drawing healthy current because they use C cells. What that current is @ 3V is unknown. We do know that it's ~ 2A @ 5V though. The best way to determine what the current draw is @ 3V is to place an Ammeter in series with the 3V battery pack. Then you'll know what they're supposed to draw.

Make sure you put your DMM on the 10A scale and use the 10A jacks!!! Otherwise you will blow the meter fuse or damage the meter.

BTW, did you read Oliver's reply? You can find them free as scrap or at least at scrap prices.

Chris

 

[scorp]

Hi,

If you can borrow a PC ATX power supply somewhere you will get a very healthy 3V3 power bus .

Olivier

Thanks sounds like the solution.

 

[scorp]

No, we don't know that. I said that those lamps are drawing healthy current because they use C cells. What that current is @ 3V is unknown. We do know that it's ~ 2A @ 5V though. The best way to determine what the current draw is @ 3V is to place an Ammeter in series with the 3V battery pack. Then you'll know what they're supposed to draw.

Make sure you put your DMM on the 10A scale and use the 10A jacks!!! Otherwise you will blow the meter fuse or damage the meter.

BTW, did you read Oliver's reply? You can find them free as scrap or at least at scrap prices.

Chris

I will test it just to see. But I'm going to use Oliver's idea sounds like the perfect solution.

Thanks

 

[CDRIVE]

I will test it just to see. But I'm going to use Oliver's idea sounds like the perfect solution.

Thanks

Yes, all over the US, every single minute that ticks by another tower is discarded for the garbage man. It's a terrible waste of good power supplies! There's copious information on the net describing repurposing them.

You have my interest regarding what those lamps draw @ 3V so please post your results. I'm guessing in the 600mA to 1A region. I base this on the fact that @ 5V it takes ~ 5 minutes to pop your supply's breaker.

Chris

 

[scorp]

Yes, all over the US, every single minute that ticks by another tower is discarded for the garbage man. It's a terrible waste of good power supplies! There's copious information on the net describing repurposing them.

You have my interest regarding what those lamps draw @ 3V so please post your results. I'm guessing in the 600mA to 1A region. I base this on the fact that @ 5V it takes ~ 5 minutes to pop your supply's breaker.

Chris

I just tested it and it it drawing about .67 amps. The batteries where weak though they totaled 2.4 volts. so all the lights didn't light or where dim.
Thanks for the help gentleman. Looking forward to hanging out here and leaning more.

 

[CDRIVE]

I just tested it and it it drawing about .67 amps. The batteries where weak though they totaled 2.4 volts. so all the lights didn't light or where dim.
Thanks for the help be ventral gentleman. Looking forward to hanging out here and leaning more.

Benvenuti a bordo!

Chris

 

[scorp]

Thank you CDDRIVE and Olive2222 for your help, I found a computer power supply and got it to work. After figuring out why it wouldn't turn on just by plugging into the wall. Lol Google helped me with that.