Help with school project - Page 1
Forum section: electronics / beginners

author: vigemien
author_rank: Newbie
timestamp: May 04, 2022, 04:18:35 am
content: I need some help, I want to run a pump (6v) and a fan(12v), with two 9v batteries and both switches. I'm a beginner and don't know how to connect them efficiently, my pump keeps blowing and I don't know why. I tried parallel and series but the fan doesn't give much power. If someone can help me thank you if you respond.

author: ledtester
author_rank: Super Contributor
timestamp: May 04, 2022, 04:43:32 am
content: A bunch of questions...What kind of school project is this? An assignment? term project? science fair show-and-tell project?What other components are you allowed to use? Resistors? capacitors? transistors? voltage regulators? DC-DC converters?Can you post pics of the pump, fan and 9V batteries you are using?Do you have to use 9V batteries to power this project?

author: vigemien
author_rank: Newbie
timestamp: May 04, 2022, 04:59:59 am
content: My project is a term project about a fan cooling system using water, and recycled materials. for example I used a box to do the setup. The pump is connected to tubing which interacts outside the fan which causes a cooling effect on the air the fan releases.I'm allowed to use anything but my problem is affordability. The product is about helping people purchase this "product" but is only a prototype. it has to run about 15 dlls which is the price of my "competition" in the market. connecting the batteries directly to the fan and pump has been a challenge since I already used all my budget.I wanted to use 9v batteries because since is a portable option and affordable for the "customer" to just replace them since some of the people who will use my product are people who are not able to connect to a power source, for example USB method or plug it in.I figure that if I used two 9v batteries = 18v and fan(12v) + pump(6v)=18v would be a good idea. I guess it was not and don't know how to fix it, is there any recommendation as to what to use that is inexpensive to solve my issue?also thank you so much for your response, I will take pictures now to attach.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 04, 2022, 08:00:10 am
content: Having the pump and fan in series only works well if the current consumption is the same. Even than there can be problem on start up.9 V batteries are relatively expensive energy sources as they don't have much capacity. A first point would be to check the power consumption on the 2 parts and check how long the batteries could last.A 12 V fan may well run with 9 V, though at reduced speed.Cooling often calls for a longer run time and thus if possible more mains power (e.g. a wall wart) than battery power.

author: MarkF
author_rank: Super Contributor
timestamp: May 04, 2022, 10:49:50 am
content: As others have said, 9V batteries can not supply much power.But if they last long enough, you would be better off not running the pump and fan in series.A couple of caps and regulators would be better for low current usage:

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2022, 10:58:59 am
content: The 7806 is marginal run off a 9V battery, because it doesn't provide enough headroom for the voltage drop as the battery discharges.The problem with connecting the batteries in series and running the fan off one of them and the fan off both is, they will discharge at different rates.It's always better to avoid having more than one power supply voltage, whenever possible. 5V fans are widely available and cheap and your pump will probably run fine from 5V, so use a 5V plug mounted supply, or USB power bank, if you need a battery. This also helps if you want to add a micro controller to your project and there are plenty which will work off 5V.

author: MarkF
author_rank: Super Contributor
timestamp: May 04, 2022, 12:10:10 pm
content: Quote from: Zero999 on May 04, 2022, 10:58:59 amIf the differing discharge rate turns out to be a problem, the 7806 is capable of running off the 18V input.

author: themadhippy
author_rank: Super Contributor
timestamp: May 04, 2022, 12:18:11 pm
content: 2 6v batteries in seriesQuoteAs the manufacturer you dont need to include the battery's that's down to the customer who didn't see the smal print on the box "battery's not included"

author: Terry Bites
author_rank: Super Contributor
timestamp: May 04, 2022, 01:43:29 pm
content: Get some AA or AA batteries and pile them up.And an 8X or a couple of 4x holders. Wedge (or solder) a wire in at the 6V point on an 8X.No power losses and so much less hassle.~ $10

author: antenna
author_rank: Frequent Contributor
timestamp: May 04, 2022, 01:57:13 pm
content: Take a look at this...https://www.powerstream.com/9V-Alkaline-tests.htmYou will see that, for most 9v batteries, the voltage drops well below 9v almost immediately after a load is connected.Also, most of the cheap 12v fans available run between 80mA and 200mA. Add a little water pump to that and you are now discharging the batteries in the 500mA range which, at .3mAh for the most expensive 9v batteries, will not make it a whole hour.Is it economical to pay $10 for a set of batteries when they will only last for maybe one hour and achieve negligible cooling effect? You should shift your project toward proving to the world why such devices are a waste of money rather than compounding the economical and environmental problems by creating another scam product.Edit: you should also note comment #2 at the top of that web page I linked to. It states that these types of batteries are intended for low current draw, not what you are trying to do. That is probably why you assume they will last longer than they really will under the conditions you propose. It's a bad idea all aroundand I don't say that to be rude...

author: free_electron
author_rank: Super Contributor
timestamp: May 04, 2022, 03:46:56 pm
content: Quote from: MarkF on May 04, 2022, 10:49:50 amyeah, burn whatever little power those 9 volt blocks have in linear regulators...

author: MarkF
author_rank: Super Contributor
timestamp: May 04, 2022, 05:22:10 pm
content: Quote from: free_electron on May 04, 2022, 03:46:56 pmCan't you do anything but criticize? Where's your solution?An alternative could be two6V batteries.Just need to find a battery holder for them.

author: james_s
author_rank: Super Contributor
timestamp: May 04, 2022, 05:31:32 pm
content: 9V batteries are a terrible choice, they are very expensive for the power they produce and they are incapable of delivering very much current. Get some C or D battery holders and use those, or even just AA batteries, any of those choices can deliver much more power than a 9V and you will have a lot more options for voltage since they come in 1.5V increments. You cannot get 6V out of a 9V battery without a regulator and that's going to result in additional waste and loss of efficiency.

author: janoc
author_rank: Super Contributor
timestamp: May 04, 2022, 05:41:06 pm
content: Quote from: MarkF on May 04, 2022, 05:22:10 pmAn alternative would be finding a way how to not have to use a voltage regulator in the first place. Pump and a fan are hardly something that requires a regulated voltage source.And if you do have to use one, at least use a switching regulator. Any of those cheapo Chinese modules or RC model "BECs" will be a better solution than anything using those 78xx linear regulators you have proposed - that 6V regulator is going to be dropping whopping 12V if you put those batteries in series as you have mentioned. If at only 500mA (which is likely very conservative, given that the OP is driving a motor), that's 6W of power you are using to heat the surrounding air. Out of crappy 9V battery which doesn't have much capacity to begin with.

author: Zero999
author_rank: Super Contributor
timestamp: May 04, 2022, 05:42:52 pm
content: Quote from: MarkF on May 04, 2022, 05:22:10 pmHe's right. Burning a load of power in linear regulators is a bad idea. Don't take it personally. Numerous other possible suggestions have been made.An alternative is a 12V battery and a buck regulator to get 6V for the pump.https://www.romanblack.com/smps/smps.htmQuote from: janoc on May 04, 2022, 05:41:06 pmYes, use 5V or 6V and a 5V fan. They're fairly common and aren't any more expensive than the 12V variety.

author: vigemien
author_rank: Newbie
timestamp: May 04, 2022, 06:58:17 pm
content: Thank you for the visual connections, I looked up the capacitors and the regulators, and are very inexpensive, I will add these to my project. some people suggested changing my fan, pump, or power source but as I mentioned my budget is almost close to zero as I do not work to finish school. I learned my lesson for next time to not use 9v batteries which it seems was a bad idea.Thank you to everybody who took the time to answer my question, I learned a lot just by reading at the responses and the links included. Appreciate it!!

author: antenna
author_rank: Frequent Contributor
timestamp: May 04, 2022, 11:52:27 pm
content: I hesitate to make an alternative suggestion seeing the OP set on making this happen, but I would also like to add that evaporative cooling only works if the relative humidity is below 70% (and only efficiently if below 20%). What might be better is using a pot of water to absorb the heat from the hot side of a Peltier module and take the cool air off the cold side with an aluminum heat sync and fan. At least in that situation you are competing with ambient temperature, not the relative humidityThose will not run on 9v batteries though..If the relative humidity were low enough to make evaporative cooling effective, I'd just stick my t-shirt under the faucet for a second and put it back on slightly damp. That's something prison will teach you because they don't spring for air conditioning, lol. You wanna learn how to stay cool on a budget, go to the joint! You'll even learn to save your plastic bags from commissary so you can keep your stuff (Mountain Dew, Pepsi, etc) clean when you flush twice and set it in the John, hahahaha!!! Been there, done that!

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 05, 2022, 07:05:32 pm
content: You need 6 and 12V just use D batteries for that. You can use 8 D for the 12V and 4 D for the 6V. Simple enough. No need for voltage regulator.

author: mariush
author_rank: Super Contributor
timestamp: May 05, 2022, 08:10:38 pm
content: I would say just use a 12v lead-acid car/motorbike battery or a VRLA (UPS) battery.Doesn't look like size is an issue, and you won't need to constantly recharge C batteries, 9v batteries are too crap...A 12v fan will accept at least 10% above, so 13v won't damage it .. but if you're worried about it you can put 1 or 2 diodes between the battery and the fan so that if you charge the lead-acid battery with 13.8v, the fan will see around 12..13v.For the pump just use a buck (or otherwise called step-down) dc-dc converter, you get your 11..14v down to 6v easily.You could get some cheap solar panels that output around 15v or more when it's sunny, and use a basic adjustable linear regulator to limit the voltage going to battery to maximum 13.8v and you get bonus points for charging the battery in the field.

author: tepalia02
author_rank: Regular Contributor
timestamp: May 07, 2022, 12:28:09 pm
content: I think you'd better share a circuit diagram or a close photo of your circuit.