Battery back-up?
pcrobot
Posts: 103
I'm trying to find a way to power my stamp with batteries in case the power goes off (and the AC adapter stops supplying power) and resets my program.
Any suggestions would be appreciated!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.
Any suggestions would be appreciated!
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Robotics
ro-bot-ics (noun)
the science or technology of robots, their design, manufacture, application, use, etc.
Comments
http://webpages.charter.net/schwabelove/BasicStamp/5V-UPS-PowerSupply.gif
That reminds me.... we just moved and changed our service provider. That link will eventually die.
I will try to get something (a copy) at our new provider sometime this weekend or point to a corner
of Parallax's web-space.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
There is a question of which kind of battery.
If No recharge is wanted, Alkaline will likely give you the longest, most economical in a small package when used with the Schotky diodes.
With recharge, lead acid Gel Cells are still the best for tolerating abuse, holding a charge for a long time and the easiest to trickle charge, but they are not dense [noparse][[/noparse]not small and portable] and they may take a bit longer to recharge. They also come cheaply in huge sizes which means a very long backup.
Both NiMh and Lithium batteries should never be run down to zero as suffer a chemistry change. Lithium need to shut off at about 2 volts. I am not sure about NiMh, but never reverse the charge current, 2 volts is probably a good cut off for them too.
NiMh are getting more and more power all the time into their small packages and recharge quickly. Very good easily store bought solution. If there is ever a problem, just throw away a bad cell and put a new charged one in the holder. In a pinch, you can use Alkaline [noparse][[/noparse]recharger off]. A recharged set can be swapped easily whole or piece meal. A trickle charge can work. But if it is too low [noparse][[/noparse]below 1/50th of the rated output], it will possibly reduce the battery's recharge capacity.
Lithium is wonderful for portablity, but seems to need special chips to recharge or an expensive charger. Otherwise, explosions! The batteries are expensive too. I would consider using a pair of old cell phone batteries and a matching charger. If someone buys a new phone, these things are often available to recycle. One Lithium cell can power the Propeller.
Also, you can get an old emergency stair light and remove the charger. You will have a good trickle charger and maybe a good battery together. But be careful as many of these are not isolated and the hot wire can pack a dangerous jolt. Care should be taken to see that the regulation is adequate and the voltage is not excessive.
Beau's scheme has an isolation transformer and more regulation. Better or best if your a hobbyist. I would love to see an 8 volt version though as I use 8 volt lead acid Gel Cells [noparse][[/noparse]I suppose you could just add 4 diodes to the first regulator, but I am not sure if the 6v Lamp is intended to protect something].
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 6/24/2006 11:37:25 AM GMT
The Lamp in this circuit allows it to act as a float charger for a Lead Acid battery.
This has an effect of·reducing some of the stress to the battery during a charge.
An 8V version could be done with 7 diodes. What I did to determine the "charge"
voltage was to consider that it takes about 13.8V as a charge voltage for a standard
12V battery.
13.8V / 12V = 1.15
....for 6V ...
1.15 * 6V = 6.9V
6.9V minus the 5V from the regulator you get 1.9V
1.9V divided by .6V (diode voltage drop), you get 3.17
So....
Diodes = ((1.15 * Vbat) - 5V) / .6V
Diodes = ((1.15 * 8V) -5V) / .6V
= 4.2V / .6V
= 7
At some point though, you may just want to consider using an adjustable regulator for
the first stage instead of "tricking" a 5V regulator to produce a different voltage level.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
Post Edited (Beau Schwabe (Parallax)) : 6/24/2006 3:03:14 PM GMT
I thought the lamp was doing that, but since it is a 'non-linear' device I am still a bit uncertain if I should be using a 12Volt/1amp or some other value. Thinking in differentials and limits is not my strong point.
Incidentally, I cannot locate a·6v/1amp bulb.· I can locate 6v-5watt; 6v-15watt;6v-25watt etc.· These are all automotive [noparse][[/noparse]or motorcycle].
Here is what I have come up with.
My 'best guess' tells me that the 6Volt/1amp (or 5 watts) will usually work fine, but it is merely a guess based on the idea that the battery may never get to a low enough voltage [noparse][[/noparse]below 3.2volts (9.2v-3.2v=6.0v)] to require a higher voltage rating.
I still wonder what would happen if I forgot to include the battery [noparse][[/noparse]let's say I was servicing the unit and tried to 'hot swap' a battery]. Without a battery, it seems like the bulb would be at 9.2 volts and then might act like a fuse (depending on the actual load). So, I am thinking that a 12Volt/1amp·(10watt)·bulb is better as it will remain intact.
I also wonder if the 1amp should be adjusted to vary the charge rate.
I know these things have a fairly wide range, so I am thinking the 1 amp is still okay [noparse][[/noparse]since the 7805 is thermally limited to 1 amp output]. Still 6v x 1a = 6watts and 12v x 1a =12watts.
In terms of power dissipation, it seems the 12v at 1/2amp (5 watt) would be closer to an equivalent. I don't expect to find a 10 volt bulb selection and I am not even sure I will have much choice in 12v bulbs either.
Obviously, I don't expect the 12 volt bulb to glow brightly in this context.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 6/24/2006 4:46:03 PM GMT
in operation right now that is using a replacement bulb for 12V outdoor landscape lighting....
Which by the way happens to be the exact same bulb used in my Jeep's 3rd brake light.
And yes, the bulb "should" glow very dimly, especially when the battery is near charge.
The current rating of the bulb is not much of a problem, because under charge the bulb
is never going to be pushed to that extreme.
If the battery is missing or you have a "dry cell" the bulb becomes a fuse with your load.
If your battery is very weak and it is under charge, the bulb still acts like a fuse but it also
becomes an automatic current limiter protecting the battery as well as the charger. This is
because the filament will exhibit more resistance, the brighter it glows.... substituting a
fixed resistor in it's place will not have the same effect.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
There are some small automotive 5 watt bulbs that actually fit into a fuse holder as 'panel lighting'.
The 20 watts may make for a higher trickle charge as it consumes more power, but that seems okay.
I did some reading. Things are becoming clearer.
The Art of Electronics mentions that the Lead Acid Gel Cells are quite happy to trickle charge at 1/1000th of their capacity current (unlike the NiMh which take on a 'memory' from a low trickle charge of somewhere around 1/30th to 1/50th their capacity). The gel cells are fairly tolerant of a sustained 'quick charge' too. So the wide range of the light bulb isn't a problem with them.
After everything is built and the battery is stable, I can use an ampmeter to find the right bulb.
I plan on using this with an 8volt/9amphour battery. This allows me to add on several 7805s [noparse][[/noparse]which according to the PDFs really need 7volts to properly regulate].
I think the LM2940-5.0 might be a better regulator choice for the 6volt BU battery's final regulator as it is low dropout [noparse][[/noparse]And it has several nice features: including automatic shut-down if you install a reversed battery].
Everything I read about the 7805 indicated that regulation may cease below about 7volts, so I wonder what that second 7805 is actually doing between at 6.8volts which below the 7 input limit.
From all I have read, I keep returning to the idea that the Lead Acid Gel Cell is the optimal back up battery.
In unpredictable situations [noparse][[/noparse]like Solar Cell trickle charging] it can accept more persistently low level charges and put them to use without any problems. They can operate for 8-10 years in a trickle charge role and the extra capacity allows for icy cold days and longer periods of no available charge.
The NiMh and Lithium are much better for mobile appliances and small robots that can protect the battery by shutting down when the battery is near a low level. Then swap out or immediately recharge. They don't seem to have the right chemistry for most backup, but they really can move a small robot with less burden of weight.
Forgive me for being quite lengthy, but there are always newcomers thinking about all sorts of battery setups.
For me, this has settled about 2 years of thought on the subject.
I have had a lot of trouble locating charge circuits for the 8volt Gel Cells.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Post Edited (Kramer) : 6/25/2006 8:51:40 AM GMT
I have some 12 volt relays that actually turn off at 3.4 volts, and turn on at 7, so experiment with relays to find where they turn on and off. Since the 7805 doesn't work below 7, no point killing the battery. I use a smart floating charger with two states, fast charge and slow charge, with leds that indicate which state it is in. With large batteries it never ever goes to red(fast) on my project using nema 23 servo motos. There is no switching, just charger>battery>78xx>project.
A schematic of the relay design would be helpful. The only one I have seen doesn't provide a floating charge - just toggles on and off at a predetermined voltage threshold.
And, it seems that any and all batteries survive better when charged and even the lead acid batteries don't like being below 50% for long periods of time [noparse][[/noparse]they become sulphated]. So oversized BU batteries are better than undersized.
I wish I could find a good reference text on battery charging, but all the vendors want to sell more batteries and more expensive chargers -- so it is hard to find a 'generic' 1950s style discussion of the engineering pros and cons. Everything is getting very proprietary.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"If you want more fiber, eat the package.· Not enough?· Eat the manual."········