72v to 12v DC/DC converter needed

[1000w]

I want to power up a 12 Volt car stereo cd/tuner on my cargo bike with a 20S LiFePO4 pack (72volt).
Anyone know how many amps an average car stereo draws?
I have already blown up a Lyen 60volt converter on this pack, all it took was an absent mind and about 7 seconds connected to the pack with nothing connected to the output, resulting in an unpleasant loud pop and burnt cap smell.
I have seached the forum and can't find info on a possible 72V unit.
The perfect unit would also be able to supply around 8.4 Volts for my Magic shine head light or can a resistor be used on the 12 Volt supply to drop it down to 8.4? The light doesn't draw much power.
Any info will be much appreciated.

 

[amberwolf]

If you use a low-power amp like 50W or less, then that is less than 5A max on the speakers. If you never turn it way up or don't have a lot of bass (or EQ it out), then probably a lot less. You may well be able to use a simple 12VDC LCD monitor ac adapter, if you have one that will accept 110 or 220VAC (most of the ones I've seen will).

However, you might want to look for some of the older Toshiba or IBM laptop adapters that are 15VDC out, as that's closer to the ~14V that most automotive stuff actually runs on while the car engine is running the alternator. Some of them are at least 3A, and I recall one from a decade ago that was 5A, for the old gray Satellite and Tecra series. With 15V output, you could parallel two or more of them using diodes, and the diode will drop the voltage down as well as help protect the supplies from each other in case of failure (internal short, etc).

A 12V Meanwell might work too.

To determine the power usage of a stereo amp, use your watt meter on your (or a friend's) car battery with jjust the stereo running at about the volume levels you expect. If you don't turn antyhing else on, and have the doors shut so lights are off, it should give you mostly just the stereo usage.



The light's 8.4V would be better created using an LM317 with a heatsink, running off the 12-15V; while it wastes a fair bit of power as heat it will be better than a resistor doing the same thing, easier to calculate the values to give you the right votlage without worrying about frying the light. I'd still fuse the light with a fast-blow rated for just at or just above what the light actually draws, so that hopefully if somethign happens to the regulator and it pushes full voltage to the light, the excess current draw will blow the fuse and protect the light.

 

[SamRam]

EBay a 12-13v switching power supply and hope it runs on Your relatively low-high voltage.
Led string china 24 dollar 18 amp thing works golden on my bike.
Ask what the lvc is.

Cheers

Sam

 

[Alan B]

Magic Shine lights have been discussed before, search for it. They have a built in regulator and can handle a range of voltage. I have not tried it but I've read that 12 volts will work.

 

[docnjoj]

Magic Shine lights have been discussed before, search for it. They have a built in regulator and can handle a range of voltage. I have not tried it but I've read that 12 volts will work.

Yep. I use 13 volts for my MS and Dr Bass mentioned they can handle up to 18 volts but I can't see using that much voltage.
otherDoc

 

[miuan]

I am using this one with my 20S lipo pack
http://www.ebay.com/itm/110665942376?
It works but gets quite warm. I think if you don't use it over 5A, it should be okay.

 

[1000w]

Thanks everyone for the great replies.
I'm happy to hear that the MS lights are fine with 13V.

EBay a 12-13v switching power supply and hope it runs on Your relatively low-high voltage.
Led string china 24 dollar 18 amp thing works golden on my bike.

So these switching power supplies will run on DC??? What voltage do you run yours on SamRam?
I recently bought one of these, http://www.ebay.com.au/itm/12V-30A-360W-switching-power-supply-driver-LED-light-strip-AC-DC-transformer-/270980525125?pt=AU_B_I_Electrical_Test_Equipment&hash=item3f17b2ac45#ht_4981wt_1013 to run my RC charger.
If people are sure it won't blow on 70V DC I might try it out then get another one if it works.
Cheers,

 

[Reactor]

I had the same problem and found this product. Have bought it but not received it yet but it seems like the best fit.


http://www.aliexpress.com/store/pro...-12VDC-10A-72V-Electric/313864_522806594.html

 

[1000w]

I had the same problem and found this product. Have bought it but not received it yet but it seems like the best fit.


http://www.aliexpress.com/store/pro...-12VDC-10A-72V-Electric/313864_522806594.html

These look like great value at $11.00US. the only thing I don't like is using my credit card, I wish they had Paypal.
Can you let me know when you get yours?
Cheers.

 

[Reactor]

The vendor is legit as I have bought from him before but I will let you know anyway.

 

[miuan]

I had the same problem and found this product. Have bought it but not received it yet but it seems like the best fit.


http://www.aliexpress.com/store/pro...-12VDC-10A-72V-Electric/313864_522806594.html

I had one of these, it bit the dust too soon at 5A continuous. That's why I recommended another product in my earlier post.