hi peeps
ive decided to build the voltage regulator board but im clueless about the voltages
ill be using a TS 7805 CZ reg , a larger capacitor in front and a smaller one after ... but how do i decide on the capacitor size?
i want a steady 5v supply for my machine and i have a choice of 6 rechargeable AA batteries (7.2v) or 8 AA's (9.6v) ... i'd prefer to use the 7.2v as i could swap it later for some battery packs i have (when i find a way to charge em) but it just makes the 2.0v vdrop... whereas the 9.6v version makes the 2/3 vdrop some peeps say is better...
any idea's?
oh and could you explain how you came to the conclusion as i'm more used to biological fluid logic rather than maths based logic.
thanks peeps
dom
I can’t help with logical cap choice, but,
go with the rechargeables. They have more current capacity that alkalines all day long. Have you read the datasheet? It should list the suggested capacitors in a default configuration.
still erm
i did look at the sheet but it gave the same capacitors for all thier regs (from 5 to 24v) which struck me as odd - there must be some kind of specification …right? (sheet said 0.33uf then 0.1uf)
when you say rechargeables you mean the AA’s right (the packs are also rechargable when i finally build some way of connecting them to a mains adaptor) - i was wondering if 7.2v or 9.6v really made much of a difference.
maybe im misswording - this may take some time 
dom
Doh!
For some reason I thought you were considering using either rechargeables or alkalines. The extra voltage will be wasted. Go for the 7.2. Even lipos come in 7.2v flavors.
gotta luv the shoutbox
acording to the guys
the first capacator can be pretty fluid (from 0.3uf - 10uf sounds ok) - like a bucket with a hole in it, the size of the bucket aint that important
the 7.2v seems better than the 9.6v as there will be less energy wasted as heat
i do love the open source brain
thanks guys
dom
Tis done
My first ever soldering experience (its a damn site harder than i realised - mines seriously messy)
looking thru my collection of capacitors i realised that after all that fussing i didnt have the right ones anyway so i reverted to my fluid biology logic and picked ones that looked nice.
i then proceded to solder two other pcb’s which i had built (a wire to pin convertor and a alternative DIP attatcher) after which my eyes hurt and i was knackered (english term : too tired to care anymore)… so i’ll take a multimeter to them then test em out in the next few days and tell you if it melts a hole in my desk.
dom
You could try a Low Drop Out
You could try a Low Drop Out (LDO) voltage regulator, which will give you a little more headroom before the 7.2V battery drops below where the chip can operate.
Try this post for some more info.
turns out it all works
it would appear my steady hands have served me well again
one thing i did notice tho… the steady output takes a sec or two to be truely steady (i think cos i used a larger electrolytic capacitor than i initially aimed for) - im hoping this doesnt mess up the picaxe when i eventually link them in…we shall see (i hear the words “zener diode” floating around in the ether - i think i’m getting the hang of this electronics thingy)
hmmm - maybe not getting the hang
turns out i missunderstood how a zener worked - i thought it only let current thru after it reached a certain voltage… turns out that is true but i didnt realise it also kept hold of the dropout voltage too - ie a 6v one confronted with 7.2v would only let 1.2v thru
eeesh … and i made the discovery after i bought the damn things - there a LOT of really bad youtube videos and descriptions around.
any ideas what i CAN use to hold off the current from the volt reg till the capacator has fully charged?
dom
You can still make use of a
You can still make use of a Zener diode by using it as the trigger to a complementary latch, along the lines of this example.
Your circuit doesn’t need to use quite as many parts as that one, but the basic idea is that the latch will be turned on via the Zener (replacing the N/O switch), and stay on until the power supply is disconnected, or at least drops to a very low voltage.
If you decide to make your own version of this circuit there will need to be a few modifications but we can help you with that. One option is to replace the transistor that will be driving the voltage regulator with a MOSFET or even a relay, to allow it to handle the current required.
i think i get it
so i use the zener to trigger a transistor which will then allow current to the volt reg.
problem is that the current fluctuates while the cap charges…which then causes dips in the volt reg output - maybe some form of timed pause would make more sense (as a zenner based system would allow output every time it fluctuates above the zener’s trigger) as after about 5secs the whole thing seems to sort itself out.
basically i just dont want output till the caps fully charged
one question - how long does an electrolytic capacitor hold onto its charge (cos it might not happen again - this was just my first attempt) or is it drained by the rest of the circuit once the power source is removed
ahhh - its all one big learning (crying?) experience
dom
The cap will discharge
The cap will discharge itself very quickly if the load (voltage reg.) is still connected after the power is removed.
The cool thing about the latch is that when the Zener triggers transistor #1, transistor #2 gets switched on by transistor #1 as well. Then, because the two transistors are connected back to back, transistor #2 works in parallel with the Zener to keep transistor #1 turned on.
Since transistor #1 is now keeping transistor #2 active and vice versa, the latch created by the complementary transistor pair will stay on (latched) until power is removed, even if the supply voltage falls below the Zener threshold.
If you set the circuit up so the Zener switches transistor #1 on only when the cap is almost at full charge, you should get the delayed start effect as intended, without having to worry about the timing being incorrect.
erm…ok…?
i’ll have another look to try and decode what you just said (after all the whole point of project blue beta is to learn)
however
i woke up the other morning thinking “why not just put a ceramic capacitor between the electrolytic one and the volt reg to smooth out the fluctuations” (i do that a lot - i must dream in tech).
so i used my new soldering iron to stabilise the connections of all the various parts rather than doing it breadboard style then hooked it up to the multimeter - and suddenly there was no fluctuation - not sure if its because of the soldering or if its no longer an unused capacitor but the problem seems to have sorted itself out for now
do electrolytic caps hold onto a residue after thier first charge or get altered in some way that makes later use smoother?
(i doubt it was the soldering if i’m honest as i was pretty carefull first time about the connections - but the scientist in me never likes to leave out a possible affecting circumstance)
dom
Multiple capacitors
Multiple capacitors connected in parallel will tend to behave like a single capacitor, but with capacitance equal to the total sum of the capacitances. This isn’t always exactly how it works, especially with diferent types of capacitors connected together, but the real deal is usually pretty close.
I know electrolytic capacitors tend to lose their capacitance as they age, but I haven’t heard of them having to warm up or anything like that when you first use them. I think they’d probably charge and discharge them a few times when first manufactured, but maybe that’s only done for the high performance electrolytics use in PCs and such.
Either way I’m glad your problem has been sorted out =)
Maybe the new soldering iron was the trick? Cold solder joints can have very poor conductivity even if they look ok on the outside.
combination
the caps combine? bugger…there goes that understanding (i was hoping to smooth one using another) - it does make sense tho i suppose.
the caps im using were given to me at my first attempt (amber alpha?) at electronics about ten years ago by my little bro who worked at Tandy when it went bust so i dunno if age was a factor
thanks for your help tho - i can feel my brain getting bigger every day thanks to you lot and your advice (might explain the headaches and the goo oozing from my ears)
