Hello,

I have a vacuum cleaner which works with batteries and I use it for cleaning inside my car. The problem is that the yield is too short only around 10 minutes with fully charged batteries.

Now I would want to connect a plug for the 12Vdc car´s connector and use this source as power supply. I have checked the power when my car is running at this plug and there are 14,4Vdc.

I aslo checked that the vacuum cleaner uses a motor which consumps 7A at 3,6Vdc (3 batteries in serial) so I have thought about the possibility of installing a power transistor which takes the 10,8Vdc at its Vce or Vds. I think is necessary to use a MOS transistor but I don´t work usually with them so I´m not sure if that is possible to do.

For example I found a IRFZ44R which I think has enough properties to do it but I would like to confirm the way of connecting it. Can you help me?

Thanks and best regards.

__________________
Regards from Mallorca.
You´ll never know enough...

 

I have seen numerous descriptions of 3 terminal voltage regulators such as the LM317 with a pass transistor to handle larger currents. As I recall, the datasheet for the LM317 has just such an arrangement shown. This might be one way of solving the problem.

__________________
stevez

 

The heat generated by burning up 10.8v at the amps used by a vac is very high. This is 70W of heat! It would need a big transistor (actually several transistors) and heatsink. Much simpler to just get a 12v vac. The cost of doing this is quite high.

__________________
I thought what I'd do was I'd pretend I was one of those deaf-mutes.

 

Looks like you need an switch mode powersuply.

__________________
Il give you shocking experience.

 

The cheap and dirty solution: apply serial an appropriate car-bulb seriel with cleaner. Also give nice light for work

 

Hello Stevez,

I have seen numerous descriptions of 3 terminal voltage regulators such as the LM317 with a pass transistor to handle larger currents. As I recall, the datasheet for the LM317 has just such an arrangement shown. This might be one way of solving the problem.

I checked the maximum Iout from this LM317 and it´s only 1,5A. I know there are some voltage regulators which could do this function but they use to have drop voltage at output and they are more expensive than a transistor.

Hello Oznog,

The heat generated by burning up 10.8v at the amps used by a vac is very high. This is 70W of heat! It would need a big transistor (actually several transistors) and heatsink. Much simpler to just get a 12v vac. The cost of doing this is quite high.

I already checked that we would have so much heat at the transistor but this IRFZ44R I already checked it supports at least 100W and I found some more which supports more than 100W. The cost of installing a MOSFET there should be cheap, it´s around 2 or 3 euros and the vacuum I have I got from fuel station BP card points, so it´s like free. I also do it to learn I little bit more.

Hello Someone Electro,

Looks like you need an switch mode powersuply

I think it´s not necessary, I only want to excitate the MOSFET with some resistor and the 14,4 Vin to have the 10,8V at Vds and then get the 3,6V / 7A at the motor... It seems easy.

Hello Sebi,

The cheap and dirty solution: apply serial an appropriate car-bulb seriel with cleaner. Also give nice light for work

In fact, it´s not a bad idea but the problem is that the motor needs exactly 3,6Vdc and 7A to have the maximum yield and I don´t think I can find a bulb so accurate to the final values I need.

You can see the vacuum cleaner, I don´t have a lot of place inside, just enough to fix there some MOS transistor and resistors to excitate it... I think that is the best option but I still need to know the way of calculate and connect the MOS transistor to the resistors and Vin to get this 10,8V at its Vds. Any idea???

Thanks for your answers.

Attached Images

vacuum_cleaner_philips_pelican.jpg (307.1 KB, 726 views)

__________________
Regards from Mallorca.
You´ll never know enough...

 

If you try to regulate it linear you will have to get rid of 75W of energy.

So if you use an transistor or sotming on an 1 C°/W heatink(Such an heatsink is already quite big and heavy)The transistor wod be runing at about 90 to 110 C° and this is very hot.

An swicthmode powersuply is from 80 to 90 % eficent wich means there is very litle heat made and so it can be smaller,lighter and cooler.

__________________
Il give you shocking experience.

 

The dissipation of analog supply exactly same as bulb disipation. Without really big heatsink cannot work. With heatsink impossible to build into this case. The SMPSU is a solution, but maybe also not enough place in case for it. Don't worry about 3,7V, it will happy with 3,5...4,2V. I know only this type for 10A:

Attached Files

l4970_118.pdf (399.6 KB, 12 views)

 

I would use a "Pulse width modulation" circuit to control the power from the larger battery.

__________________
I No Longer accept Private Messages on here.
All Emails to me Must Contain the Word \"Electronic\" in the \"Subject Line\"
or they go Directly to my Junk Mail Folder.
Email me at: chemelec@hotmail.com
Website: http://www3.telus.net/chemelec

 

Yep this cod also be a solution.

And you can use power MOSFETs.

__________________
Il give you shocking experience.

 

Yes, Just go to the Projects on my Website.

__________________
I No Longer accept Private Messages on here.
All Emails to me Must Contain the Word \"Electronic\" in the \"Subject Line\"
or they go Directly to my Junk Mail Folder.
Email me at: chemelec@hotmail.com
Website: http://www3.telus.net/chemelec

 

Hello,

now I have a doubt, I checked that the motor used nearly 7A when was running from its 3,6Vdc battery source but when I simulated the power with my power supply and I put 4,4Vdc it consumps nearly 8A and the propeller turns faster, more rpm!!!!

As Sebi said this motor has a range and I think the interesting thing would be to know the maximum voltage I can supply it. Then I would get maximum rpm, maximum cleaning vacuum (very important to remove the dirty at the car) and less problems to connect it to the car´s power supply. The motor is a Johnson with numbers 62855 and 3F1113. I already tried to find the data sheet for this one using those numbers but I couldn´t find anything.

I connected already a MOSFET (IRFP350A) with 2 resistors without heatsink to do the test but as you said the heat is too much and in some seconds the component gets so hot that the soldered point I had at the drain pin was removed. This MOSFET supports 17A Ids as maximum and it´s not so big but the problem is to cool it as you said, not possible to install anything inside the case. Maybe the cheapest option would be to make a box where I put this MOSFET circuit with a heatsink. The box with car´s plug male output cable and normal plug male output cable to connect at the vacuum cleaner, where I should also install a female normal plug and a switch, or even the switch could be at that external box.
What do you think about this solution?

I don´t know how big should be the heatsink to dissipate the heat properly...

__________________
Regards from Mallorca.
You´ll never know enough...

 

Hello,

I would say this would be enough to dissipate the heat (1,5ºC/W):

http://www.amidata.es/cgi-bin/bv/sea...chText=2342514

__________________
Regards from Mallorca.
You´ll never know enough...

 

get an MOSFET that can suply more curnet.If its high enugh it will be just warm whithout an heatsink.

the IRF3205 can suply 110A at 55V and its in an TO-220(This is like most power transistors and voltage regulator) Over here you can get it for $2.

__________________
Il give you shocking experience.

 

Beware Sebi,

The 110A spec is a marketing spec. The TO-220 pins CANNOT support 110A of continous current.