An inductor in the circuit will smooth off the ripple nicely. It is the voltage across the load that is of any concern. Once connected across a battery, I have seen the voltage start as high as about 19v and drop towards 13v when fully charged. The voltage with no load could measure as high as 40v but end up at 17 across a 12v battery discharged 50%.
On 2013-12-10 7:35 PM, "oak" <oak_box@yahoo.com> wrote:
Hmmm...
I'm very concerned about 2 aspects:
1) I've heard rumors that at least Li batteries should NOT be connected to a charging source that has a lot of RIPPLE in it. If you have a blocking diode to prevent the battery from being drawn *down* during the low portions of the wave, is this ok??
2) I'd also be concerned about charging any battery with a much higher voltage source. People might think of this as being a "current source, and who cares what the voltage is", but still... How much higher in voltage from the source to the battery is it ok to go?
John
From: Dave Steere <dcsteere@dcsteere.com>
To: electricboats@yahoogroups.com
Sent: Tuesday, December 10, 2013 2:10 PM
Subject: Re: [Electric Boats] Inexpensive variable power supply?
One super cheap way to accomplish this works just fine for me. I found an old, beat up "smart charger" for automobile batteries. Most of these come with a current meter on front and switchable outputs for "trickle," "normal charge," and "start." Remove the "smart components. It's usually a small circuit board with various hard-wired charging routines for lead acid (AGM, gel cell, Flooded and maybe a few other choices).The built in rectifier is typically a single diode and the huge transformer is ceter-tapped to provide three or more voltage settings. Replace the single solid state diode in there with a bridge rectifier (A 50 AMP BRIDGE DIODE ARRAY - 4 DIODES can be bought for less than a dollar if you shop around).Now, simply install two switches. The center tapped output of the transformer can let you choose two different output voltages, one exactly twice what the other pair of terminals delivers. So one of your switches can switch from HI to LO. The other switch switches between the various leads that used to provide different voltages for trickle, charge and start. So you have 3 voltages at the "LO" setting and another 3 voltages at the "HI" setting of switch 1. So that gives you six distinct output voltages ranging from around 8VDC to around 54VDC. A filter capacitor is optional. I ended up putting in a 100 microfarad electrolytic that I happened to have in my junk pile. The transformer in mine provides a solid 15-20 amps at just about any voltage I select. While it's not continuously adjustable, and it doesn't come with current limitation settings, that can be fairly easily added later, but for my uses (36 cells of LiFEPO4 in my EV), it gives me the flexibility to charge anywhere from two to eight cells at a time at a fairly substantial current (15 A, or in some cases, at lower voltage, it comfortably provides 20A). Not a bad idea to mount your bridge rectivier on a big heat sink and put a computer fan in the enclosure. It does get pretty warm but never dangerously hot. Also make sure you put in a fuse to prevent damage. But hey, if the whole thing burns up, all you've lost is a garage sale purchase of a pretty crummy cheap-o battery charger, something that's easily replaced.On Tue, Dec 10, 2013 at 1:48 AM, Orest Iwaszko <orestyko@hotmail.com> wrote:
Love that , not only will it charge your 12-30 volts you asked for but also every other rechargeable battery you own , as well as be a power supply for any other small implement you own as well . These are worth their weight in gold. ( another thing that gets me as excited asa variable power supply is the desulphating charger ) But nothing gets me as excited as all of you yahoooo!is there a variable power supply in the 120 - 180 volts neighbourhood ?ps love your quote.On 2013-12-09, at 4:44 PM, Kirk McLoren wrote:there usually are various supplies on Ebay. If you are lucky you might find an HP"The further a society drifts from truth the more it will hate those who speak it."
George Orwell
On Monday, December 9, 2013 4:34 PM, Mark F <mark.internet@yahoo.ca> wrote:
Have you looked at a bench power supply.Here is a link to one http://www.leeselectronic.com/index.php?id_product=1422&controller=productI purchased the 60V one and have used it to charge some batteries.Unfortunately it is max 5A.There are DIY versions online of modifying old PC power supplies, but I don't think they will do 10A or 30 Volts though.If you find a good source, let us knowMark
From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, December 9, 2013 1:42:54 PM
Subject: [Electric Boats] Inexpensive variable power supply?
I've been experimenting with rolling my own power supply, using an Arduino to control on/off, voltage monitoring, etc.Is there a good, relatively cheap VARIABLE power supply that will output something in the range of 12-30V, up to at least 5A, preferrably 10A?It should run off 90-150V (dock shore power, which should be expected to be "dirty").Thanks!John
--
All the best,
Dave Steere
dcsteere@dcsteere.com
850-234-2540 office
850-319-6010 cell phone
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