Well now I’m kicking my self. I’ve been planning on building a robot at somepoint and am hoping to throw in a miniitx mobo to manage all the control/coms etc. For this task I purchased the picoPSU 80W 12v DC-DC ATX PSU a while back and it works great with the mobo, HDD, slim optical drive…

But today I was chatting with Bob about power regulation off three of his SLAs, wired in parallel of course, and how he would regulate the output to 12vdc. Even though I suggested a fairly funky way of achiving this…it hit us that he would have to go about DC > AC > DC (regulated to 12v)…and this is simply OTT and inefficient.

16:11:37 Bob: i have a question for you, i have three batteries, connected in parallel
16:11:42 Me: shoot
16:11:48 Bob: 12v batteries
16:11:51 Me: SLAs?
16:12:02 Bob: the output varies between 11.8v and about 14v
16:12:05 Bob: yeah
16:12:06 Me: right
16:12:24 Bob: i need a way of pulling 12v at 3 or 4 A out of there
16:12:43 Bob: i need to regulate it, but without the drop out a regulator gived
16:12:46 Bob: *gives
16:12:54 Bob: any idea how i’d go about it?
16:12:56 Me: why is the dropout a problem?
16:12:59 Me: heat or?
16:13:10 Me: cause 14 to 12v isn’t a huge amount of heat
16:13:23 Me: 2*4 ~= 8 to 10W
16:14:06 Me: the other alternative is to find some power diodes capable of say 5A
16:14:11 Bob: well, if the batteries are outputting 12v, and the regulator uses 0.7v for itself, i’ll only have 11.3v to play with
16:14:15 Me: string ‘em in series along the + line
16:14:34 Me: I get you
16:14:36 Me: but then again
16:14:47 Bob: and thats not enough to power the computer, it has to be within like 0.5v
16:14:48 Me: the regulators will only work @ 12+1.2v
16:14:55 Me: approximately
16:15:08 Me: if the voltage drops below that threshold, they won’t be able to regulate
16:15:52 Me: what you could do
16:15:56 Me: is have a regulator line
16:15:59 Me: and a comparator
16:16:26 Me: if the voltage is above min required for regulation, then regulate it
16:16:33 Me: else, swap to direct source off the bats
16:16:39 Me: via a relay tbh.
16:17:04 Me: does that make sense?
16:17:10 Bob: aye, seems to
16:17:25 Me: just ensure all your high current bits have proper wiring
16:17:34 Me: and the low dc stuff no worries
16:17:38 Me: tbh a tiny PIC would do the job
16:17:45 Me: or you could go analog if you want
16:17:57 Bob: if the voltage can be regulated to 12v, regulate it, otherwise, toggle the relay to direct power
16:18:26 Me: yup
16:19:06 Me: so say our Vreg_min = 13.2v
16:19:19 Me: you can have 3 branches
16:19:34 Me: (1) supply to vreg if voltage > 13.2v
16:19:58 Me: (2) Vs > 12v but < 13.2v
16:20:04 Me: you'll have to pass through a branch of diodes
16:20:08 Bob: if there isnt enough voltage to power the vreg, what output will it give? none, or a lower voltage?
16:20:08 Me: you can get high power ones!
16:20:14 Me: (3) direct flip to Vs
16:20:41 Me: none to 1.2v tops, but my money is on none

Actually it seems that both our monies are going to be on the picoPSU-60-WI 6-26V 60W DC-DC ATX PSU model capable of operating between 6 to 26V which is simply fantastic! Not only does this mean we don’t need to bother with regulating the power but we can just monitor the voltage and once it hits a threshold, an MCU can instruct the mainboard to shutdown.