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Nov 22, 2009, 10:42 PM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
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Question

Can a car battery charger be used as a 12V power supply?


I have an old Sears 6/12V 6A car battery charger, it outputs @14.4 V DC. When I hook up my Multiplex LN-5014 charger to it, the charger gives an input voltage error, though the manual lists the input voltage at 11-15V. Curiously, my GWS-MC2002 nimh/nicad charger works fine with it, what's up with that? I've even tried powering the Multiplex from the GWS and I get the same error, (the Multiplex works fine from a 12V battery or car accessory adapter). Obviously I'm missing something here. I'm getting tired having to charge everything in the car, and I want to avoid having to buy an all new AC/DC charger or a power supply, (probably the cheapest option), or a heavy deep cycle battery. I have a separate balancer/watt meter for balancing. Any ideas or sage "don't ever do that!!" wisdom? Thanks,

Sonny
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Nov 22, 2009, 10:55 PM
Registered User
Car battery chargers have a tendency to put out really dirty DC and there have been reports of damaged chargers as a result of this. Some are better than others in this regard and you may use a 12V battery as a buffer to smooth out the power form. Even an old battery removed from a car usually suffices.

In the long run you'll likely be far better served in obtaining a power supply or deep cycle battery.

Mark
Nov 22, 2009, 11:10 PM
Registered User
omnicomps's Avatar
I just picked up one of the harbor freight car battery chargers. Is it OK to run this charger on a car battery and charger at the same time? I have an old car battery that I can use.
Nov 22, 2009, 11:12 PM
Registered User
Typically yes. The car battery will smooth the output of the charger and it should work just fine.

Mark
Nov 22, 2009, 11:18 PM
I just want to fly
justwanttofly's Avatar
i use a computer power supply pushes 12 volts at 7 amps dose great with my b-6 that only needs 5 amps i can run my charger and a buddys of mine at the same time its awsome if you would like to see it i could post some pics of it tommorrow. it has an off and on switch. it works great. and very easy to make.
Nov 22, 2009, 11:24 PM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
Thread OP
Quote:
Originally Posted by mrforsyth
Car battery chargers have a tendency to put out really dirty DC and there have been reports of damaged chargers as a result of this. Some are better than others in this regard and you may use a 12V battery as a buffer to smooth out the power form. Even an old battery removed from a car usually suffices.

In the long run you'll likely be far better served in obtaining a power supply or deep cycle battery.

Mark
Thanks, I tried the charger into a 12V 7ah gel cell & then into the charger & the Multiplex still freaked, though it worked fine from the gel cell alone. Problem with the gel cell is it doesn't have the capacity to do more than 1 or 2 charges before it needs recharging, (pia), (charging 3S 2200mah lipo). I do have a Radio Shack 350W 12A PC power supply*; one of the 4 wire connectors coming out of it, (it has a bunch of different voltages & connectors coming out of it), has 2 hots & 2 negs @12VDC each on a 4 pin connector. Could I cut that connector off & get two 12VDC out of it? Geez.... the lengths I go to in order to save a buck!! Thanks,

Sonny

*Here's a link to the Radio Shack Power Supply I have: http://www.radioshack.com/product/in...ductId=2284639 . Should I try & use this?
Last edited by sonny1; Nov 22, 2009 at 11:45 PM. Reason: Link to Radio Shack Power Supply
Nov 22, 2009, 11:38 PM
Registered User
videocruzer's Avatar
i use a real old one with a ten amp charge. i just use a car battery as a balist.
i used my micro orbit,HC gt a8's and my new 208b with it. the 208b gets a little paulsy at higher charge rates.
the gt a8 has ferrit thing on the input wires the 208 does not,
Nov 23, 2009, 02:51 AM
Proud to eat Kraut ;-)
Julez's Avatar
rule #1:
Use the right tool for the job. Car battery chargers are not made to power RC chargers -> do not use them for this.

Chip Hyde burnt down his garage by using the integrated charger of a jump start unit as a charger power supply. go figure.
Nov 23, 2009, 03:11 AM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
Thread OP
Quote:
Originally Posted by Julez
rule #1:
Use the right tool for the job. Car battery chargers are not made to power RC chargers -> do not use them for this.

Chip Hyde burnt down his garage by using the integrated charger of a jump start unit as a charger power supply. go figure.
Juelz, thanks for the reminder! I've used that analogy myself many times, and I really shoulda known better. What do you think about my using the Radio Shack Power Supply I mentioned and linked to in post #6? I don't want to cut any connectors off of it if it won't be appropriate for the job. Darn, I knew that switching to lipo would probably be another "black hole" in my wallet; oh well, I'm committed now! Thanks,

Sonny
Nov 23, 2009, 03:19 AM
Registered User
Even though you measured (or it specifies) 14.4v output, the voltage will typically drop as soon as you apply any load. How far it drops depends on the charger and on how many amps the load is. Your Multiplex may be more sensitive than your GWS so far as input voltage is concerned, or it may simply be taking more amps so that the car charger voltage is dropping further.

I used to use a car charger connected to a smallish car battery as my 12v source for my plane charger. But when charging a large battery I would eventually get an "input voltage error" message as the car battery ran down and the car charger was unable to keep up with it. I also got an "input voltage error" message sometimes if I was taking too few amps and the car charger/battery voltage got too high.

My solution was to buy a ProPeak stabilised 20A supply unit http://www.modelsport.co.uk/?CallFun...n&ItemID=23410 . Its voltage will not vary significantly whatever amps you ask it to deliver (within its limit).
Nov 23, 2009, 04:06 AM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
Thread OP
Quote:
Originally Posted by abenn
Even though you measured (or it specifies) 14.4v output, the voltage will typically drop as soon as you apply any load. How far it drops depends on the charger and on how many amps the load is. Your Multiplex may be more sensitive than your GWS so far as input voltage is concerned, or it may simply be taking more amps so that the car charger voltage is dropping further.

I used to use a car charger connected to a smallish car battery as my 12v source for my plane charger. But when charging a large battery I would eventually get an "input voltage error" message as the car battery ran down and the car charger was unable to keep up with it. I also got an "input voltage error" message sometimes if I was taking too few amps and the car charger/battery voltage got too high.

My solution was to buy a ProPeak stabilised 20A supply unit http://www.modelsport.co.uk/?CallFun...n&ItemID=23410 . Its voltage will not vary significantly whatever amps you ask it to deliver (within its limit).
Why hello Great Britain! Thanks for you input abenn! What you described is exactly what's been happening, I will look for a ProPeak, but at a US dist to save a little on shipping, lol!! Before that though, I'm going to investigate this Radio Shack PC Power Supply I've got here on hand. I bought it for it's intended purpose, but never used it. I can still take it back for a refund at this point, but if I cut a connector off just to see if it will, (or will not), work for me then I'll be stuck with it. It's rated at 350w & 12A discharge, but has a whole gaggle of bundled wires w/ various connectors coming out of it for attachment to different PC hardware; all of them attached to the mother board w/ no lug or bare wire output attachments. One of those connectors is a 4 wire connector with two DC 12V+ & two DC 12V- leads. I've seen other similar units where they've removed the connectors and replaced them with Deans or others for RC use. The other option of course is that I sell the Multiplex, the balancer, take the power supply back for a refund, and go out and buy a decent all-in-one AC/DC balancing charger. Like I said last post.....black hole in my wallet stuff! It seems I have this pesky disease called RCAS, (Radio Control Aquisition Syndrome); do they have that disease on your side of the pond? Thanks for your response, and have a great day today!

Sonny

PS: BTW: How can a power supply rated at a regulated output of 12V DC, charge up a 3S Lipo pack to a full 12.6V? Seems like a PC supply would regulate 12V to maintain exactly 12V, so where is that extra .6V coming from? Again, am I missing something here?
Last edited by sonny1; Nov 23, 2009 at 04:28 AM. Reason: Another question BTW:
Nov 23, 2009, 04:23 AM
Kool Kats Fly RC!! AMA 30462
sonny1's Avatar
Thread OP
Quote:
Originally Posted by justwanttofly
i use a computer power supply pushes 12 volts at 7 amps dose great with my b-6 that only needs 5 amps i can run my charger and a buddys of mine at the same time its awsome if you would like to see it i could post some pics of it tommorrow. it has an off and on switch. it works great. and very easy to make.
Pics would be appreciated, maybe it will give me a clue of how to adapt the PC power supply I have to work the same way as yours. Thanks,

Sonny
Nov 23, 2009, 05:51 AM
Proud to eat Kraut ;-)
Julez's Avatar
Hi Sonny!

Quote:
What do you think about my using the Radio Shack Power Supply I mentioned and linked to in post #6?
Again rule #1 should be applied.

A PC power supply is not made to power chargers, as well.

You might want to read my little write-up concerning power supplies:

https://www.rcgroups.com/forums/show....php?t=1082910
Nov 23, 2009, 05:53 AM
Stuart
srnet's Avatar
Quote:
Originally Posted by sonny1
PS: BTW: How can a power supply rated at a regulated output of 12V DC, charge up a 3S Lipo pack to a full 12.6V? Seems like a PC supply would regulate 12V to maintain exactly 12V, so where is that extra .6V coming from? Again, am I missing something here?
The electronics in the charger boost the voltage.

For instance my NiCd/NiMh charger works from 12v and that can charge up to 24 cells, which needs around 34v ..............
Nov 23, 2009, 06:30 AM
Registered User
Quote:
Originally Posted by sonny1
Why hello Great Britain! Thanks for you input abenn! What you described is exactly what's been happening, I will look for a ProPeak, but at a US dist to save a little on shipping, lol!! ...
I believe ProPeak is available in the US, but there's lots of other reputable brands with similar specs too
Quote:
Originally Posted by sonny1
... Before that though, I'm going to investigate this Radio Shack PC Power Supply I've got here on hand. I bought it for it's intended purpose, but never used it. I can still take it back for a refund at this point, but if I cut a connector off just to see if it will, (or will not), work for me then I'll be stuck with it. It's rated at 350w & 12A discharge, but has a whole gaggle of bundled wires w/ various connectors coming out of it for attachment to different PC hardware; all of them attached to the mother board w/ no lug or bare wire output attachments. One of those connectors is a 4 wire connector with two DC 12V+ & two DC 12V- leads. I've seen other similar units where they've removed the connectors and replaced them with Deans or others for RC use. ...
There's lots of people using PC power supplies for their chargers. I haven't done it myself, but if you search in this forum for "PC power supply" you'll probably get a lot of good info.
Quote:
Originally Posted by sonny1
... RCAS, (Radio Control Aquisition Syndrome); do they have that disease on your side of the pond? ...
'fraid so
Quote:
Originally Posted by sonny1
... PS: BTW: How can a power supply rated at a regulated output of 12V DC, charge up a 3S Lipo pack to a full 12.6V? Seems like a PC supply would regulate 12V to maintain exactly 12V, so where is that extra .6V coming from? Again, am I missing something here?
I think someone's answered that already, but the electronics in your charger can multiply the input voltage to whatever it needs for the pack you're charging Some very simple chargers -- usually designed for NiCad or NiMh packs -- can't multiply the input voltage, and are thus limited to charging packs which are less than 12v.


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