SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Jun 08, 2008, 06:26 PM
Registered User
Torrance
Joined Feb 2005
1,409 Posts
Discussion
using car charger as a power supply

hey there, I was wondering if it's ok to use a sears 20A automotive battery charger as a power supply for my astroflight charger. it puts out a lot of amps but I'm not sure if it's a steady 12-14volts output. guess I'll have to measure it.

also wondering if these lead acid chargers pulse the output voltage?
JustinONE is offline Find More Posts by JustinONE
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 08, 2008, 06:53 PM
Permanently Banned
San Jose Ca / RSA flyer
Joined May 2003
8,030 Posts
NO GOOD, too much RIPPLE, will trigger intermittent operation, not gonna get a good stable charge, may even stop half way

use regulated SWITCHERs, cheap, compact and powerful

U can find them at any surplus ~ 20 bucks
hall woo is offline Find More Posts by hall woo
Reply With Quote
Old Jun 08, 2008, 06:56 PM
early retired & loving it
USA, AZ, Kingman
Joined Aug 2005
1,229 Posts
Do not use this as the astro charger source.
A battery charger is usually only 1/2 wave charger and is just not stable to use as a source. It will cause a lot of NOISE and can damage the astroflightr charger. On a scope you would see pulses going from some very low voltage to 13-15V.
bnrusso is offline Find More Posts by bnrusso
Reply With Quote
Old Jun 08, 2008, 07:12 PM
Registered User
Torrance
Joined Feb 2005
1,409 Posts
ok cool, good to know.

I will try the regulated switches.
JustinONE is offline Find More Posts by JustinONE
Reply With Quote
Old Jun 08, 2008, 08:16 PM
PGR
Low AltiDude
PGR's Avatar
United States, CA, Costa Mesa
Joined Jun 2004
7,949 Posts
You can use that car charger if it's connected to a decent car battery, though. The battery will stabilize the output and act as a pretty good filter and voltage regulator. The battery doesn't even need to be a real good car battery as long as it doesn't have any bad cells in it. Just keep it ventilated and full of electrolyte, and it's a good idea to blow a lungful of air at the top while you connect or disconnect any cables. Charging a lead-acid battery produces Hydrogen which is explosive in any kind of concentration and while extremely rare, a spark can blow the top off a battery which typically gets acid all over everything.

Just to put this in perspective, I was an auto and heavy equipment mechanic and electrician for well over 25 years and I only saw one battery pop. That one time was enough, though, so I blow before I connect or disconnect which virtually eliminates the chance that the Hydrogen can be in a a strong enough concentration to ignite.

Pete
PGR is offline Find More Posts by PGR
Reply With Quote
Old Jun 09, 2008, 02:01 AM
Registered User
Letchworth, Great Britain (UK)
Joined Jul 2004
11,710 Posts
Quote:
Originally Posted by PGR
You can use that car charger if it's connected to a decent car battery, though. The battery will stabilize the output and act as a pretty good filter and voltage regulator. ...
That may work, but my experience was that my charger used to cut out due to too-low or too-high input voltage as the car battery became fully charged if my charge rate was low, or started to run down if I was charging at too many amps for the car charger to keep up I replaced that setup with a Ripmax 20A stabilised psu.
abenn is online now Find More Posts by abenn
Reply With Quote
Old Jun 09, 2008, 09:03 AM
PGR
Low AltiDude
PGR's Avatar
United States, CA, Costa Mesa
Joined Jun 2004
7,949 Posts
There's no question that a proper regulated power supply is the correct way to go, but if the car battery and car battery charger are good ones and working properly, there's no reason why they won't work equally well. In fact, I can legitimately argue that a power supply which includes a storage battery is safer:

Power grids are subject to both momentary and long-duration brownouts and blackouts which can also affect an R/C charger's charging cycle. In some instances, one of the momentary interruptions can cause an R/C charger to re-start the charge cycle. If the battery pack which is connected to the R/C charger is already fully-charged, this could trigger a situation where a LiPo pack becomes overcharged because some LiPo chargers run in dumb-mode for the first few minutes of a charge cycle. This, for example, was the case with the original AstroFlight 109 chargers.

But a DC power supply which includes a storage battery would basically act like an unterruptable power supply and the R/C charger would never see a power interruption.

So there!

That said, I use a 50A 13.8V switching power supply and I retired my old AstroFlight charger long ago.

Pete
PGR is offline Find More Posts by PGR
Reply With Quote
Old Jun 09, 2008, 01:42 PM
Registered User
Letchworth, Great Britain (UK)
Joined Jul 2004
11,710 Posts
Quote:
Originally Posted by PGR
There's no question that a proper regulated power supply is the correct way to go, but if the car battery and car battery charger are good ones and working properly, there's no reason why they won't work equally well. In fact, I can legitimately argue that a power supply which includes a storage battery is safer:

Power grids are subject to both momentary and long-duration brownouts and blackouts which can also affect an R/C charger's charging cycle. In some instances, one of the momentary interruptions can cause an R/C charger to re-start the charge cycle. ...
Ah, but ... if the R/C charger and PSU are "good ones and working properly" they won't notice a momentary brownout/blackout, and they won't recommence the charge if the power comes back on after a long-duration one

Anyway, I think we're on the same wavelength
abenn is online now Find More Posts by abenn
Reply With Quote
Old Jun 09, 2008, 02:18 PM
Registered User
Torrance
Joined Feb 2005
1,409 Posts
I do have a couple old car batteries that won't charge up past 12vlts, maybe a bad cell, would this work as a good buffer.
JustinONE is offline Find More Posts by JustinONE
Reply With Quote
Old Jun 09, 2008, 07:28 PM
Registered User
Wallingford, Ct
Joined Sep 2001
1,913 Posts
Bad batteries should work. The batteries are a big capacitor. Look at the size and number of their plates.
Al M is offline Find More Posts by Al M
Reply With Quote
Old Jun 09, 2008, 08:44 PM
PGR
Low AltiDude
PGR's Avatar
United States, CA, Costa Mesa
Joined Jun 2004
7,949 Posts
A bad battery typically just loads down a charger output without actually storing any energy. Unless the battery charger has a greater output than the battery itself is consuming, there won't be any power left to run an R/C charger.

The last bad car battery I tried to charge drew 20A continuously from a 25A charger and it never quite reached 12V. That was with nothing but the car charger connected to the battery. I was charging it with a 25A charger so theoretically, there was only 5A of power left to run an R/C charger.

The bottom line is it's typically not a good idea to use a bad battery to buffer the output of a car charger. You won't need a perfect battery, but you will need one that will accept a full charge which is widely recognized as 13.8V at 2A or less input.

Pete
PGR is offline Find More Posts by PGR
Reply With Quote
Old Jun 10, 2008, 01:25 AM
Registered User
Torrance
Joined Feb 2005
1,409 Posts
good to know, thanks
JustinONE is offline Find More Posts by JustinONE
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Using my car charger as a power supply question cat5 Batteries and Chargers 24 Nov 17, 2005 08:14 PM
using a car battery charger as a power source? foss1997 Power Systems 14 Jan 10, 2002 09:56 AM
battery charger as 12v power supply sandman Power Systems 6 May 09, 2001 03:15 AM