You'd think, after having worked in broadcast maintenance and other related fields for well over a decade, I'd be better at any of this, but I'm not. I can (for the most part) read a schematic, do some troubleshooting, etc., but couldn't design a circuit to save my life. No idea why. Maybe I have an aversion to serious math. I am more on the creative side. It happens.

Here's the scenario.
• I work part-time at an electronics supply place. We just got a mistakenly-ordered box of 12v, 4.5Ah SLA batteries of the sort one finds in a UPS and such. I get them at cost. M is annoyed at having ordered the wrong ones, so he's more than happy to unload them off to me.
• I've been resurrecting my photography business that I put on hold to spend what seems like forever in the music business. I have studio strobes, but am way too light on the portable stuff.
• I love building my own stuff, fixing my stuff as much as possible.
• I'm building up my arsenal of off-camera flashes (OCF). These run at 6 volts, use AA's.

You can see where this is going?


I can't decide if I want to run two flashes off one battery for a long time, or one flash off the battery for an insane amount of time, i.e., longer than a photo session. If I go with the first option, I'll need a circuit that can provide two separate 6v ports; the second option, a 12v-6v DC/DC converter. The batteries being cheap enough (for me, anyway), I may try and do two of each...two 2-bangers, and two 1-bangers.
Again, I work in a supply house, so I have crazy access to crazy amount of stock. And if I'm presented with a schematic, I can build the beast, no problem.

For those 'in-the-know' the flash units I'm using (to start with) are the much-revered Vivitar 283's. I have four; I go on scavenger binges from time to time and pick them up as I find them. Eventually, I'll be picking up some new units, probably the Yong Nuo line from China (really? What a surprise. )
The 283's need some good heft to a supply so the recycle times can stay short. New AA's give me a recycle time around 2 seconds from full pop to full pop (naturally it's rapid-fire if I'm on a lower power setting), but that doesn't last very long, of course.

I just need to go mobile. ASAP.
So, any of you fine folks who can give me a starting point, or for whom an entire circuit is the sort of task to be scribbled out while sitting at a stoplight, your assistance is beyond greatly appreciated.

Thanks!
Dave

 

Once one of the six 2V cells in my 12V gel cell fails and I manage to get a 10V cell afterward.

I'm not saying anything more.

 

This is reasonably simple:

It's a 6v buck-type supply; about 92% efficient.

It does need a minimum load of about 25mA to keep the output voltage stable. Less than that, and the output voltage will climb. As shown, output is about 6.2v.

A linear regulator such as an LM317 would be terribly inefficient, and would overheat during rapid shoots.

[eta]
I've attached the LTSpice .asc file so that you can run the simulation if you'd like. Google "LTSpice Download"; choose the link to Linear Technology. It's freeware. You don't have to register it or anything.

There's an LTSpice Users' Group on Yahoo! Groups. LOTS of available models and help there.

 

Do you have / need a complete schematic for the older / original Viv. 283's ? I have detailed information on them.

 

I tend to go with Wookie's idea, SMPS regulators are highly efficient, and will work well for this.

 

Do you have / need a complete schematic for the older / original Viv. 283's ? I have detailed information on them.

I could use it, yes! That would be great. Mine are all original series, with the trigger voltages dangerous to DSLRs, so I use the Cybersyncs to trigger. What I'd like to do is bypass the battery compartment, and either install a DC jack in the side somewhere or reconfigure the AC adapter port for this application. Plus, it would just be nice to have the documentation.

 

Well, I'll stay away from the 317 regardless; I can't get too rapid on the shooting anyway, because the flash tube can overheat and introduce a whole new series of problems.
SgtWookie, just from my cursory glances through the forum since discovering it last night, I had a suspicion you'd be one of the first to step up to the plate. Thank you!
I see this is the 1-banger circuit. Is a 2-banger possible but kinda impractical, or...?
I don't mind, either way.

 

I could use it, yes! That would be great. Mine are all original series, with the trigger voltages dangerous to DSLRs, so I use the Cybersyncs to trigger. What I'd like to do is bypass the battery compartment, and either install a DC jack in the side somewhere or reconfigure the AC adapter port for this application. Plus, it would just be nice to have the documentation.

OK.......I think I could dredge up my folder........we are in the closing end of a major remodel of the house, so my camera shop / hidey-hole is packed away, tho' this stuff I keep in a file cabinet that is currently inaccessable.

Question is, how involved do you want to get

 

did you say "hidey-hole" ?

Sgt wookies design is a rather good one.

But I have to say that eblc1388 has a good idea.

It isn't safe for the n00b to go fiddleing around inside a battery, but you could easily get two 6v batteries out of each.

Snip the connector between the 3rd and 4th cell and route them through the top.

You now have two 6v batteries, and no circuit losses from linear or switch-mode regs.

 

Not so noob that I couldn't go modding a battery. If I could regularly repair CRT monitors at the station--I hate flybacks, just so you know--a battery isn't gonna scare me.

I forgot to mention that I've also got a supply of 6v SLAs that I found in the dumpster outside of a commercial lighting company; new-in-box, unused, but a little dated. I plan on messing with them, too. But first, the 12v's.... I suppose I need longevity a little more than flexibility, as a priority.

 

Re-wire the 12v into parallel 6v That will give you twice the 6v current rating.

 

You're not always going to be so lucky as to be able to modify most batteries.

 

Yeah, these batts don't lend themselves to tinkering.

 

I see this is the 1-banger circuit. Is a 2-banger possible but kinda impractical, or...?
I don't mind, either way.

Ahh, not quite sure what you mean?

The LT1171 is good for up to about 2.5A output current. I suppose you could wire several of your flashes up in parallel on the output; I don't know what their current draw is though. However, if you place heavy loads on those 4.5AH SLA batteries, you'll heat them up a good bit, which will shorten their life span.

Keep in mind that you don't want to discharge your SLA batteries more than about 30% if you want to get the maximum service life out of them. If you discharge them to 50%, you'll cut their service life by 2/3.

Check out this entry about lead-acid batteries I made over in the General Electronics Chat forum:
http://forum.allaboutcircuits.com/showpost.php?p=262143&postcount=38

Note that to use the spreadsheet effectively, you'll need to plug in the numbers from your batterys' particular datasheet, as data points can vary considerably even within a particular manufacturers' product lines.

Back to the circuit I posted; it's a switching buck-type regulator. It needs a couple of volts over the output voltage in order to work properly, or the output voltage will drop under load. As drawn, it should work fine for input voltages within the range of 8v-36v.

 

Ahh, not quite sure what you mean?

Sorry. I'm a bit vague because I'm somewhat simplistic/old school. I was thinking about divvying up the 12 into 2 distinct 6 volt circuits. Wasn't really thinking about parallel. Which is fine.
Bottom line, I don't want to run more than 2 flashes off any battery. This is mostly for efficiency where equipment hauling and setup/teardown is concerned. It's also about having enough juice for each flash, to last for at least the whole length of the shoot. I figure I can also keep better track of resource use during a shoot.

 

Keep in mind that you don't want to discharge your SLA batteries more than about 30% if you want to get the maximum service life out of them. If you discharge them to 50%, you'll cut their service life by 2/3.

Well, the beauty of where I am at present is that I do not expect to have to use these in this setup for more than a couple of years; during that time, I expect to have made enough money to afford commercially-made units and not worry about this stuff after that.
So, the cost is so low for me to be doing this that if they die a year and a half from now, I'm good.

 

Just remember that most flash units have a very high initial current draw if you've put them through a full power flash.

 

Well, sure. Here's what doesn't bother me, though... I can get a surprising amount of time out of a set of 4 AA's at full pop, so I'm wagering that a battery capable of 4.5 Ah is not gonna flinch much.

 

Creating a Virtual Power Supply Ground