Topic: External battery pack for MT2496?

[blindman]

Len says "With the 7805 you should use a tantalum cap on the input side for filtering and an electrolytic on the output for stability."

My question, and I will ask here first, is how to best figure out the Capacitance to use. One of teh datasheets for a 7805 I read said 22uF, I have seen others mention a higher cap mentioned.

How can you best figure out the capacitance required?

[blindman]

Just a note on the Altiods/Sucrets/DIY versions. If you use two 9 volt batteries, run them in parallel to keep voltage ~9. In series, you will be giving your regulator 18v and making it drop 13v to get your 5v out! Most of your battery juice would then end up as heat emanating from the regulator.

I learned that AFTER I made my version 1 in the Sucrets pack. I have read a lot in the last few weeks.

The goal of version 2 was to be smaller, use ONE 9V rechargeable, use an input capacitor and use a tin case with the 7805 using the case as a heatsink. I learned during the creation of USB Battery Extender Version 2 that I should have some polarity protection, but it was too late to incorporate it at that point, it was 2AM! That would have ot wait for Version 3.

So, it was later and I was moving along and being a humble man I will now admit, in public... I F'd it up and had made the space for the battery too small and here it was completed and the 9V batt would not fit. DOH! I had been so careful, but in the end I failed. I put it aside and figured, "eh, lesson learned" and went to get a new 7805 to begin Version 3. I had to grab some more 9V batt leads and noticed a holder for a "N" battery, it is like a 1/2 size AAA. I asked the guy what batter it held and they had several, from 3.5V to 12V. I thought what the hey, it would allow me to salvage the Version 2 that the 9V doesn't fit in.

This is Version 2... http://fecundswamp.peanutonastring.com/usb_batt_v2/




The battery has a little nook built in so it can be store in the bag for transport
when not in use.

You can see the screw that attaches to the standoff that attaches to the 7805...
this will act as a heatsink... I hope!

The lid does shut, it just isn't in this picture... I thought I was doinked when I realized
the lid did NOT shut after I installed the USB adapter... a quick zip with teh dremel
cutting tool an it shuts perfect.

I used the PS/2 to USB adapter again, I always knew that they would be useful someday. It has a 22uF Polyester Film Cap on the input, it uses a 10mm Standoff to connect the 7805 to the board & the tin, acting as support and as a heatsink. And this has no polarity protection, but it isn't so important now as it uses the Type 23A 12V battery. I will probably use this once and then never again, unless it lasts a really long time... the battery is like $3.80... but it really made me laugh that I could save my failure from utter uselessness. I wish I could get these in rechargeables.

I found this site useful for helping me understand the reverse-polarity issue... http://www.maxim-ic.com/appnotes.cfm/appnote_number/636

I wish I could find a site to explain how to figure out what capacitance to use though. The datasheet for the 7805 shows a 22uF cap on the input, so that is what I used... I have no idea if that is good or bad... I am dangerous, aren't I? Just enough information to F everything up.

thanx,
michael

[sanaka]

Hey Michael. That's certainly a compact battery box, but, especially with one little N battery, I wouldn't think it would give you enough extra runtime to be worth the trouble. A few other observations, which you should urgently ignore if you wish  :

Just as with two 9v's in series, using a 12v battery into your 7805 is very inefficient. You do need some 'overhead voltage' to make the regulator work, but only around 2v. With 12, that's about 5 of your 12 volts just wasted as heat.

A battery's physical size is a rough indicator of how long it will put out juice for. That tiny N battery won't run your MT for very long at all. A 9v, quite a lot longer. A few 9v in parallel could make a very worthy external juice box for a MT. For serious amp-hours, your big, boxy, heavy SLA's are the business.

I sounds like you mounted the 7805 on a standoff, away from the floor of the box. For best heatsinking, the flat back of the chip should be in full contact with the metal, with some heatsink compound smooshed in between. It might not matter in this case because the MT probably draws way less current than the 7805 can actually handle. Especially if you don't drop a bunch of extra volts across the regulator!

I'm not sure whether a momentary polarity reversal will fry the 7805. I kinda don't think so. The datasheet may say. As long as your juice box won't implode if you accidentally touch the battery leads wrong way around when you're putting in a new one or whatever, I wouldn't worry about hard wired polarity protection. Just dont have your MT plugged into the juice box whilst changing the batteries. Once they are in right you should be fine because the USB connector only plugs in one way.

I think the smoothing cap value is not critical. Pretty much bigger is better. 22uf sounds pretty big to me, like that datasheet is pretty conservative. Especially since you're running from battery so there won't be any AC ripple trying to get through.

Peace,
Sanaka

[blindman]

Hey Michael. That's certainly a compact battery box, but, especially with one little N battery, I wouldn't think it would give you enough extra runtime to be worth the trouble. A few other observations, which you should urgently ignore if you wish  :

Thanx for the feedback.

Like I said, this was me trying to recover after a terribly landing. It was late and I drilled just 5mm too much to the right when i should have drilled left. When I realized the 9V didn't fit, I was going to trash the whole thing. Then I found this battery, so for giggles I finished with it.

I had thought about putting the 7805 against the bottom of the case, and I agree, it would be more effecient... I may incorporate that into Version 3. Thanx!

I think the smoothing cap value is not critical. Pretty much bigger is better. 22uf sounds pretty big to me, like that datasheet is pretty conservative. Especially since you're running from battery so there won't be any AC ripple trying to get through.

I understand the AC ripple thing, I read that... as a matter of curiosity though I do want to understand a bit more about what values to use. I think what I am heading towards, is there a way (or need) to regulate the input voltage so when input power drops to a certain level it shuts off... or does the 7805 do that? I know the 7805 'wants' a min of 7V in, but what if the battery drops to 6V? and then even to 4v? does it simply shutdown when it can no longer output 5V?

For something I could buy for +/- $30, I am probably overthinking all this.. but I am just curious... I want to understand this stuff better.

I would also like to add to my design... a LED that is either on or off, if the power drops below 5V the LED does not light indicating battery change needed. maybe disco lights? mirror ball? ok, overthinking.

good night.

Again, I appreciate the feedback

bye,
mjr

[F.O.Bean]

chris-my only source for the 2v headroom thing was directly from leegeddy

[Nick Graham]

http://www.mrgadget.com.au/catalog/usb-device-charger-battery-box-with-flashlight-p-571.html

Would this work?

Is 5.6v correct?

[udovdh]

itsb best to have at least a 2v minimum inbetween the original power source and the ending voltage

why?

...I think it is because the 7805 needs at least 2v headroom for the regulation to kick in (read from another forum) but please correct me if i'm wrong.

Just get a more modern low drop regulator. Linear and Maxim have them.


BTW: got info about a nice external battery, info is at http://taperssection.com/index.php?topic=55120.msg735397#msg735397

I found that in the USA the battery stick I wrote about (see link) may be marketed under the I-Power brand as Multi-Purpose Charging Stick.
With this small battery we'll have no worries about long shows, festivals, etc.
Has anybody found the device on sale somewhere online?
Please post!

[Ed.]

I think i'm confused?  is the battery you speak of one that fits into the MT or an external battery pack?

I guess I'm somewhat lazy, at least too lazy to pull apart the MT to replace the battery.  I myself would rather just use something like the battery box posted on the first page: http://www.bixnet.com/usbbatterybox.html or a juice box (todd r) type device if I need power for all day at a festival.

An external device might be more cumbersome to some, but with me and my hands, pulling apart the MT and moving circuit boards to replace the battery seems like trouble waiting to happen.

Another thing to consider would be, if you put a larger battery inside the MT, would it still work properly?  I don't know much about powering, but could it be possible that the MT is only regulated for that size battery?  Also, would the battery get too warm and then end up melting something on the inside?

[udovdh]

Yes, that is why I also mention it here.
My initial quest is/was for an internal battery replacement.

For external I have the Bixnet USB box which uses AA's.
Also for external I found this battery stick, that's why I post it here as well.
Sorry for causing confusion.

[sickrick43]

I picked up a couple of the Digital Concepts PP-99's, described earlier in the thread.  While I haven't done a run-2-dead test with them, it appears they'll run this thing a LOOONG TIME for a small package.  I've run it 4.5 hours, backlight on all the time, and still had 2 lites left on the battery.

Rick

[udovdh]

Shenzhen Herocell has a Battery Stick of 2200 mAH at 5V which could work great with an MT. I am trying to obtain one.

Edit: Their site should be more functional after january 15th.

[joekar]

I have a USB 4AA battery pack for my M/T...........I also have an external ipod shuffle 2X  AAA battery pack that has a USB plug.....Haven't done any run time tests just yet but it should get me thru the first set without touching the internal battery....every little bit/amp helps...Peace

[Crumbo]

got about 15 hours (between the external and internal battery)....YMMV

akg480/ck63 > Opti-Mod V3 (24/48) > MT 24/96

this is the external battery:

[kskreider]

got about 15 hours (between the external and internal battery)....YMMV

akg480/ck63 > Opti-Mod V3 (24/48) > MT 24/96

this is the external battery:

I use that battery pack for my JB3 and love it.

[bconnolly]

got about 15 hours (between the external and internal battery)....YMMV

akg480/ck63 > Opti-Mod V3 (24/48) > MT 24/96

this is the external battery:

That runs off of USB or ....?  I just don't see anything that mentions USB on it.  I imagine it does since both you and the poster below you use it but I'm just trying to double-check here.