5v and 12 supply

[Denzel]

I am using a 1.2 Ah 12v sla bettery to power a submarine im working on to survey river / lake beds.

I need to get a 12v supply for pumps/motors/lights etc and a 3.5/5v logic supply.
I have never done this before... Ive always used two seperate power supplies,

Could someone guide me in the right direction as to what I need to make this happen?
I was thinking about using a LM340T5 (7805), But i don't know how to set it up.

Cheers

Denz

 

[papaof2]

A switching regulator would be more effcient than an LM series device, which dissipates thevoltage drop as heat.
Sure Electronics has a couple of them on Ebay:

MC34063 based, up to 500ma output:
http://cgi.ebay.com/MC34063-Based-Switching-Regulator-Adapter-Step-Down_W0QQitemZ370171238656QQihZ024QQcategoryZ66990QQtcZphotoQQcmdZViewItemQQ_trksidZp1713.m153.l1262

AX3022 based, up to 1.5A or 10 watts, whichever is smaller:
http://cgi.ebay.com/AX3022-Based-Switching-Regulator-Adapter-Step-Down_W0QQitemZ220376101998QQihZ012QQcategoryZ66990QQtcZphotoQQcmdZViewItemQQ_trksidZp1713.m153.l1262/URL] They are about $8US each, with free shipping. John

 

[BeanieBots]

Depends on what your load currents are for each voltage rail.
Any advice can only be guess work without such data.

A switcher might be needed but would be total overkill (and expense) if you're only pulling 3mA for a PICAXE.

How to connect and whatever other components (eg caps) are required will be be clearly laid out in the datasheet of whatever regulator you decide to go with.

 

[Denzel]

...

I am running 6 12v car window water pumps, (Not all at the same time!) the maximum will be two at once. Not too sure about their current ratings but I believe they need to be pulsed if in use for periods longer than 30 seconds. In terms of Picaxe s etc, I will be using a similiar approach that I used to my V.I.P.E.R. Where I have the remote control XBee pro and picaxe 18x which then talks to about 4 slave picaxe 08m's that control the pumps (on off) lights, camera movements, water sampling etc.

Hope this helps

 

[westaust55]

@Denzel,

I concur with Papaof2 and BB but . . . .
Please read the PICAXE Manuals wrt 7805 regulators.


Try PICAXE Manual 1 page 23 for a circuit digram using a +5V linear regulator.
Rev Ed have gone to the trouble of giving you a circuit.
Note that the input can be anything 8 volts DC or graeter ( >8V)

Then Google for the 7805 datasheet. If more than a few hundred milliamps you may need a heatsink on the 7805 (and any other linear type voltage regulator.

 

[Peter M]

could always go for simplicity and just use a 3xAA holder and join the 0v together.

save on all those problems with regs, stand-by power etc.

(earth, ground, -ve, negatives, black wires... just for those with varying terminologies... yes there's always someone that objects to this one! usually takes over the post)
.

 

[Colinpc]

Depending on how long you need to power the PICAXE, you could use another battery. A mobile phone battery would power the chip for a long time as only a few mA are drawn. They have a high energy density.

Refer however to other posts as to danger of inapropriate charging and short circuits. Using the old phone as a charger is safe to recharge. Your circuit would have to be constructed to remove any chance of a short circuit.

Fred

 

[Dippy]

A simple V.Regulator, plus a couple of caps and maybe a decouple cap for the PICAXE can't get much easier can it?
Three legs: IN, Ground, OUT. (= From 12V Batt, Ground, 5V Out to PICAXE).
Check the Data Sheets as said numerous times. Honest, it must one of the easiest circuits in the world

However, and based on an over-quick skim read, you will have to decide about voltage as you are using an XBee which requires 3-ish Volts. So, you may also need a second regulator for 3 or 3.3 Volts.
And if you have PICAXE @ 5V then you will need a simple level shift to the XBee serial-data-in pin (2 resistors).

I don't know if 18X is happy @3V0 or 3V3. I've heard mixed results.
And 1.2 Ah sounds a bit piddly for all this(?). So, maybe a second battery may be needed.
Good luck.

 

[Andrew Cowan]

The 18X isn't rated for 3.3V. However, I have had some 18Xs that work happily off 3.3V, while some work erratically. You will definitly need 4.5V ish to program the chips - 3.3V isn't enough.

A

 

[Andrew Cowan]

The motors will probably draw about 1 amp. Two = 2A, so the battery will last for 36 minutes. I'm guessing at the current draw. Running any other bits? I agree wil dippy that you might want a larger battery. Subs need to be heavy, so a heavier battery isn't completly a bad thing.

A

 

[papaof2]

Pulling 1A from a 1.2AH battery will probably give at most 40 minutes of power. http://dimensions.sensata.com/Application_Notes/AN202.pdf

The AH rating is typically for 20 hours (60ma for 20 hours = 1.2AH); taking more than the 20 hour rate decreases the capacity rather quickly.

Sealed Lead Acid (SLA) batteries, whether gel cell of glass fiber mat, are cheaper in the most common sizes - such as the 12 volt, 7 or 8AH batteries used in many small UPS units. If a common type battery with larger capacity will fit the space, you can get 6 times the power for about twice the price.

John

 

[manie]

To add to Dippy's post - the regulator circuit is easy, should you want more current, fit a "pass transistor" which supplies extra current at the regulated voltage. Here is a link to a circuit:
http://www.zen22142.zen.co.uk/Circuits/Power/boosti.htm
manie

 

[Dippy]

Gee, you love that circuit Manie
Spread the heat eh?

Personally, if you're dropping a long way or using a fair current then you should really consider a switching reg. If your circuit can 'stand' it then it is a FAR, FAR better way.

Or just get a fatter linear/heatsink. Sorry, but I just can't see the point for low power stuff.
This is all very straight forward and only needs 5 minutes reading up.
I can see we're going to spend more time discussing batteries soon...
You'll get it sorted some time, all the best.

 

[BeanieBots]

Oh, I think there's a lot more than just the batteries to come.

Let's see if I've got this right?
This project is a semi-autonomous submersible with on-board camera, water sampling equipment and Xbee data link back to home?

We are on post 14 of how to do the 5v regulator.
Have I missed something significant here?

By the way, while we all argue about current ratings, where is Denzel with the FACTS.

 

[Dippy]

Worrying isn't it.

 

[BeanieBots]

Only for Nesbit who stands to lose his title

Didn't DPG do one of these a while back.
Did it ever make it unaided up the Thames?

 

[moxhamj]

This is my favourite circuit. These switchers are so easy to use, but the bit I like is you don't need a heatsink. So you save money on the heatsink, plus you don't have to worry about getting rid of the heat, plus pretty much all the energy from the battery ends up in the circuit rather than being wasted as heat. The only tricky bit is finding the inductor - you need under 1 ohm and I eventually got a whole lot from a surplus store here in Australia for $2AU each, but it makes sense to get them locally. Futurlec sell the diode and the switching reg.

Then again, as bb says, if the picaxe is 3ma then just use a 100mA 5V reg. And for those windscreen washer pumps they can be driven directly from the battery with standard mosfet/relay/transistor circuits as per the picaxe manual as they are "nominally" 12V but are designed for automotive work which in reality is 12V to 14V. They also are designed for intermittent use, and will burn out after a minute or so of continuous running. I know because I tried it once *grin*.

 

[hippy]

To be fair to denzil, he did post originally at 10 o'clock in the evening on Friday so, with time zones and a weekend, a response later tonight would not be unreasonable at the earliest. It also appears that submarine ( or other multi-voltage ) projects have been completed already, but the question relates to how to use a single supply. That we are on post 18 now ( only the second page ) doesn't suggest to me that there is any intrinsic problem with Denzil's understanding or capabilities beyond having not done it before and quite reasonably seeking advice on how to do that.

 

[Peter M]

Ummmm... can I just throw in a dumb question or two????

If IT'S a submarine....... how does the rf get to and from the controller whilst it's under water? Xbee is RF not sonar isn't it? Or is that the autonomous bit, gets itself out of the mud, surfaces, waits for the next command.

If the battery (if we get that sorted) goes flat whilst under water does it sink or swim?

 

[fernando_g]

Ummmm... can I just throw in a dumb question or two????

If the battery (if we get that sorted) goes flat whilst under water does it sink or swim?

You have raised an interesting question, which is really significant.
There must be a redundant supply to operate the vessel if the main batteries go flat.

This suggests that perhaps a separate battery bank (AAA's ?) from the main power batteries are required, to maintain the Picaxe and associated control circuitry in its right operating state.

Whereas you can run a 12v pump at 6v (although sluggishly) if the Picaxe's supply goes below a certain level it will simply kaput.

 

[Andrew Cowan]

Most dynamic dive model submarines float slightly.

Static dive subs don't always float - but expensive ones often have a mechanically timed float that is released, so it can be pulled up.

A

 

[Denzel]

...

Sorry I havent been able to get on for a while.

I have read all your suggestions and im grateful for the knowledge it has provided me regarding power supplies. My original plan was to run the entire submarine of a 12v sla as mentioned, I have set up a voltage regulator MC34063 giving me 500ma however I have noticed that when the two main pumps are switched on together (thrust) the picaxe fails and the pumps then fail within half a second and the whole program resets. So in order to keep things simple ive got a seperate power supply (3 rechargeable aa's) and two recharge circuits that ive had to waterproof and connect to the outside of the sub.

In terms of communication, the Xbee is only making communication while the sub is at the surface. for example, the sub will be at the surface. The xbee (controller) will send the submarine to a new location, then tell it to sink to 1 meter above the surface (using a simple sonar kit.) and take some photos.... then rise again for its next instructions. So even if radio control is lost it will always surface, unless there are power problems.

Sorry to leave you all alone discussing my problem.

Denz

 

[Denzel]

...

and to clarify,
I am using my 12v sla with a recharge circuit
AND a 3 aa rechargable pack with recharge circuit

 

[Andrew Cowan]

...1 meter above the surface...

Above? Below, surley.

Anyway, the resetting PICAXE indicates that either the SLAs couldn't supply enough current, or that too much noise got to the PICAXE. What capacitors did you have around the PICAXE?

2.4GHz signals are not well known for working under water.

A

 

[Peter M]

Denzel@ another way to preserve power in low voltage supply is to feed it from the main battery via a diode into a largish cap (pionty end of the diode to the cap).
This cap then acts as a small battery when the main supply is temporarily unavailable.

(sorry if someones allready mentioned that here been a while since I read em all)

 

[InvaderZim]

If you only need to dive a meter, you might consider a long antenna that sticks out of the water; then you could receive without having to surface. Then again, the added drag might kill the whole thing

 

[boriz]

Could you use some form of floating antenna, a bit like real subs do?

say 2M of very thin wire > cork > antenna?

 

[Denzel]

....

I meant to say 1 meter above the river/lake bed i.e an undefined height distance the surface, communication is not an issue as it only takes place on the surface.

I am using a 220uf cap around the Picaxe,

It seems to be the current thats an issue as when I try the circuit with a 6.5 ah 12v sla I get good performance from the motors and the picaxe however the 6.5 ah sla is too big and too heavy to strap to my sub

But my current setup seems to be working with two power supplies, and theres nothing like a good dive into the hutt river if something does fail.

 

[Andrew Cowan]

Sounds like you are using cheap SLA betteries that can't provide enough current. Usually more expensive batteries can provide more current before the voltage drops.

A

 

[cvrwy]

Denzel....

I have not looked at all the posts here, but..........

Have you considered using Lipo batteries as used in RC aircraft. They are much smaller and lighter and provide a hellava greater punch than your SLA batteries.
A 3 cell Lipo is rated 11.1 v while a 4 cell is rated 14.8 v, that could be a problem for you.

For instance, this Lipo is rated 2000 Mah @ 11.1 v. It is only 4.2 x 0.9 x 1.5 inches and 6.2 oz. It's continuous amperage is rated 30c, 30 x it's Mah capacity.
The batteries could be put in parallel to get more power.

The bad part is that it costs $60 USD. They will not ship by air.

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXWPC9&P=SM

 

[Dippy]

Anyone else ever tried these? ... apologies if not available on Ebay.

http://www.abacus.co.uk/jkcm/Batteries/Sealed+Lead+Acid/EnerSys+CYCLON

I got some 9 years ago when they were still branded 'Hawker' and Gates.
They still start my Atco lawn-mower just fine

(Unlike my 2 x Cambden PRC made batteries in my UPSs which died after 11 months. Serves me right for being a cheapskate.)

 

[BeanieBots]

The bad part is that it costs $60 USD. They will not ship by air.

There's a reason for that!

@Dippy,
I never take advertisements too seriously but in this case, I can confirm that Cyclon batteries really are used in medical equipment for the obvious reasons.

Premature death is nearly always caused by the charger rather than the battery except GP (NiMh) batteries which simply are not up the claims made on the tin.

 

[hippy]

So that's what Cyclon batteries are ... My emergency lighting uses those.

 

[Dippy]

"Premature death is nearly always caused by the charger rather than the battery except GP (NiMh) batteries which simply are not up the claims made on the tin."

- very true, but sadly the claims made on the Cambden 'tin' were "designed for use in ... UPS ....".
They failed prematurely in two different makes of UPS - APC & Galatrek. Yuasa (made in I-won't-say) lasted 3 years in the respective UPSs. And in a 3rd UPS (Belkin) a Yuasa is still going after 4 years.

Conclusions?
Either:-
1. Cambden SLA are only suitable for 'magic' UPSs which may or may not exist.
2. Cambden batteries are as bad as BB's GP batteries

Lesson Learnt?
Spend the extra and buy quality. Like many customers I haven't got the time to faff about. I just want something that works reliably.

 

[BeanieBots]

Interestingly, over the last few days whilst "characterising" some UPS Pb batteries, I've made some interesting discoveries regarding the observed characteristics towards the end of charge condition.

I have noticed a very marked difference in behaviour between two (allegedly identical) batteries but of different make.

Both are 12v 7Ah "standby" type designed for UPS use.
Battery A is made by CS3 manufactured in Mexico Part# GP 1270 F2
Battery B is made by YUASA manufactured in UK Part# NP7-12

Both batteries were fully charged (float for 72 hours at 13.8v) and then given a 48Hr equalisation charge at 14.2V.
The equalisation terminal current was measured at 9mA for the CS3 but the YUASA was still pulling 56mA.

Both were then subjected to a 3Ahr discharge at 1.0A followed by a constant current charge (500mA) to 15v. The objective being to determine charge in vs charge out efficiency. Please note, do not try this at home. Charging to 15v WILL destroy your batteries.

The curious observation was the massive difference in the voltage curve during the charge process. The CS3 unit had a characteristic more on par with NiCd technology. A fairly flat voltage rising sharply close to the end with a very rapid current drop once the 15v was reached.

The YUASA unit however, showed a voltage characteristic which was almost linear with respect to charge. An important observation was that 13.8v was reached much earlier than the CS3 and after only 3/4 of the expected capacity.

I'm not saying one unit is better than the other, but they certainly have very different characteristics and as such, have different charging requirements. Hence, a UPS designed for one type, would not necessariliy be suitable for the other type. The CS3 for example, is far more tollerant of excess voltage and showed no signs of gassing even after several days at 15v.
The YUASA unit however, could be heard gassing even before 15v or full charge was even reached.

Similar tests charging to just 13.8v, showed that the YUASA unit had fully charged within 48Hrs but the CS3 required a higher float voltage to maintain the same charge level within a similar time frame. Hence, a charger optimised for YUASA units would not re-charge a CS3 in a respectable time-frame but a charger for a CS3 would damage a YUASA unit unless extra "intelligence" is employed.

The only other possiblity for this discrepancy in behaviour would be if the CS3 is actually a miss-labelled 'cyclic' unit rather than a 'float' unit but I have now performed the same tests on three seperate units with the same results of different batches.

Conclusion, only expect the manufactureres spec if also using the manufacturers specified batteries.

 

[Dippy]

Interesting and informative stuff there BB. And good points made as usual.

I take your point re "only expect the manufactureres spec if also using the manufacturers specified batteries"
- Taking the sage advice I have looked in the three Data Sheets - APC, Galatrek and Belkin. Only Galatrek (who don't exist anymore I don't think?) specified Yuasa as an example (not 'mandatory').
The others just said "12V/ 7Ah" and a physical size. I have also checked 3 othr Data Sheets from different manufs. Again, only voltage and capacity were mentioned. Sadly I haven't got all day to check every data sheet in the world - and shouldn't have to.

So, bottom line, when you are searching for batteries and you find a couple that physically fit and of the right headline specs and they say suitable-for-UPS there is the only the 'PICAXEr criterion' left i.e. the cheapest.

Conclusion: Spend the extra and stick with the Big Boys unless you have the time/skill to experiment.
But if you want confidence that the darned thing will be working in 6 months time then stick to the Big Boys.
With the BB caveat of following any manuf's recommendations of course - assuming its actually provided.
(And assuming you have carefully filed away the Manual for rapid retrieval )

Tightness often results in tears-at-bedtime and false economy.

Anyway, enough digression from me. If people wish to save 25% on cost but have to change batteries twice as often that's their choice.

And no doubt many people will be buying the cheapest batts for their solar systems too .... makes you wonder. Battery manufs must love tightfists.
Right, where's me sunblock..