Author Topic: NEED HELP (Read 5370 times)

www.am27 · « **on:** July 07, 2012, 03:29:27 AM »

Hi everyone,
I am a new member of this forum. I don't know much and when surfing net i found this forum This is an excellent forum and very informative too. I am sure i can gain some knowledge with the guidance of the kind members of this forum.

Now come to my query- I have an old 12v D.C. High speed fan (The one which use in Bus, Big police van in INDIA) and i want to use it in Power Cut.. So my Ques. is that can i connect it directly to the Battery or i have to use some kind of protection like resistor or something.. Previously i connected it to a 12v sla ups battery (fully charged) and the fan ran very very fast with cool breeze.. But i am afraid that if i connect it directly with 12v battery will it fry the fan motor? bcoz when a 12v battery is fully charged than the volt is above 12v in the battery.

so, please Help me Regarding this Because i don't want to fry the fan, but i want to use it.. so Plz Help me in an Easy way and step by step so that i can Understand.

And Yes Thanx in Advance for your Help- If this is a wrong section to ask this type of Questions than I am Really Very Sorry I am a Newbie and Don't know much About This Forum. And Sorry for my BAd English too .. Sorry Again.

Watt · « **Reply #1 on:** July 07, 2012, 04:01:44 AM »

Hello and welcome.

I don't understand your intended use of this fan. Will it be used as a air blower or a generator?

If used as a blower, you can direct connect to the battery and by adding resistance in series, you will lower the rpm of the fan due to voltage drop. Voltage / ( divided by resistance of the motor plus any added resistance in series) will give you the amperage through the circuit and this will give you an idea of the resistor wattage you will need for those in series resistors.

That extra voltage will only make the fan turn faster and as the battery voltage decreases, your fan speed will decrease. Fully charged, a sla will be around ~12.6vdc if it has been off the charge a while. The 12v rating on the fan motor is a nominal voltage and vehicle voltage range between ( lower than 12vdc ) and up to around 14.5vdc.

www.am27 · « **Reply #2 on:** July 08, 2012, 07:07:26 PM »

Oh very very thanks 4 ur reply, i want to use it as a table fan in power cuts bcoz here in my area there is too hot and in power cut the a.c. Cieling fans are off

so i need this.

Now i tried ur method wid one 1k ohm resistor but the fan would not run. But with direct conection(i.e. Positive wire of the d.c. Fan to positive +ve terminal of battery and negative to -ve of the battery) it runs perfectly so what resistor will i need? I mean the rating, and also if i run it wid thease condition directly from battery widout giving resistor or something will it fry the motor? Please guide me.

Again Thank u.

Watt · « **Reply #3 on:** July 08, 2012, 09:21:38 PM »

Quote from: www.am27 on July 08, 2012, 07:07:26 PM

Oh very very thanks 4 ur reply, i want to use it as a table fan in power cuts bcoz here in my area there is too hot and in power cut the a.c. Cieling fans are off so i need this.

Now i tried ur method wid one 1k ohm resistor but the fan would not run. But with direct conection(i.e. Positive wire of the d.c. Fan to positive +ve terminal of battery and negative to -ve of the battery) it runs perfectly so what resistor will i need? I mean the rating, and also if i run it wid thease condition directly from battery widout giving resistor or something will it fry the motor? Please guide me.

Again Thank u.

no problem direct connected. do you have any numbers on the fan you can provide? Like a model number and brand as well as amperage? 1k is a lot of resistance. Try a .5 or 1 ohm maybe 10 watt or higher. If the resistor gets too hot, you will need a higher wattage or it will open the resistor.

www.am27 · « **Reply #4 on:** July 09, 2012, 12:44:49 AM »

Bro it is local made so no big brand name on sticker its just written kp brothers and 12v d.c. Not anything else written.
BTW i will try lower resistors and will reply here.

Watt · « **Reply #5 on:** July 09, 2012, 12:53:33 AM »

Do you have a way to measure current? If so, check the fan current and report back. Will give an idea of the motor resistance and may help you zero in on a resistor value.

Frank S · « **Reply #6 on:** July 09, 2012, 04:28:30 AM »

Quote from: Watt on July 09, 2012, 12:53:33 AM

Do you have a way to measure current? If so, check the fan current and report back. Will give an idea of the motor resistance and may help you zero in on a resistor value.

Watt; unless I;m missing something
I'm wondering if the wrong questions are being asked or if your answer was not understood
any 12vdc fan made for a vehicle will run just fine forever on a 12v battery even if fully charged connected direct as you stated. 12 to 14.5v just let it make air and feel comfortable
if he is needing to reduce the RPMs for lower speed then he could use a heavy duty variable resister like was used for the heater fans back in the 50s those things can get really hot but they hardly ever burned out

Watt · « **Reply #7 on:** July 09, 2012, 07:01:08 AM »

Frank

Yes, you may be right.

As far as my last post, if we knew the motors resistance, we could easily calculate a resistor to say lower the speed by half, one quarter or three quarters. Right now, it's a guessing game and all I can do is relate that fan to something I'm use to here in the states which is between a .4 ohm motor and a 1.4 ohm motor at 12v nominal.

If he has such a variable resistor available, that would make life easy. Thanks for the suggestion.

Quote from: Frank S on July 09, 2012, 04:28:30 AM

Quote from: Watt on July 09, 2012, 12:53:33 AM
Do you have a way to measure current? If so, check the fan current and report back. Will give an idea of the motor resistance and may help you zero in on a resistor value.
Watt; unless I;m missing something
I'm wondering if the wrong questions are being asked or if your answer was not understood
any 12vdc fan made for a vehicle will run just fine forever on a 12v battery even if fully charged connected direct as you stated. 12 to 14.5v just let it make air and feel comfortable
if he is needing to reduce the RPMs for lower speed then he could use a heavy duty variable resister like was used for the heater fans back in the 50s those things can get really hot but they hardly ever burned out

Frank S · « **Reply #8 on:** July 09, 2012, 12:05:56 PM »

Quote from: Watt on July 09, 2012, 07:01:08 AM

Frank

Yes, you may be right.

As far as my last post, if we knew the motors resistance, we could easily calculate a resistor to say lower the speed by half, one quarter or three quarters. Right now, it's a guessing game and all I can do is relate that fan to something I'm use to here in the states which is between a .4 ohm motor and a 1.4 ohm motor at 12v nominal.

If he has such a variable resistor available, that would make life easy. Thanks for the suggestion.

Quote from: Frank S on July 09, 2012, 04:28:30 AM
Quote from: Watt on July 09, 2012, 12:53:33 AM
Do you have a way to measure current? If so, check the fan current and report back. Will give an idea of the motor resistance and may help you zero in on a resistor value.
Watt; unless I;m missing something
I'm wondering if the wrong questions are being asked or if your answer was not understood
any 12vdc fan made for a vehicle will run just fine forever on a 12v battery even if fully charged connected direct as you stated. 12 to 14.5v just let it make air and feel comfortable
if he is needing to reduce the RPMs for lower speed then he could use a heavy duty variable resister like was used for the heater fans back in the 50s those things can get really hot but they hardly ever burned out

posted a reply in the hijacking thread.

www.am27 · « **Reply #9 on:** July 11, 2012, 02:26:23 PM »

Thank you guys for your Reply and I measured the current it's 3.29 (it varies from start-up to idle)

i think Now you can suggest me in a Better way, And can i use potentiometer to adjust the RPM of the Fan Please Reply what Potentiometer will be right for me.

Again Thanks in advance and Sorry For my Bad English.

THANK YOU

Frank S · « **Reply #10 on:** July 11, 2012, 03:56:54 PM »

Quote from: www.am27 on July 11, 2012, 02:26:23 PM

Thank you guys for your Reply and I measured the current it's 3.29 (it varies from start-up to idle)

i think Now you can suggest me in a Better way, And can i use potentiometer to adjust the RPM of the Fan Please Reply what Potentiometer will be right for me.

Again Thanks in advance and Sorry For my Bad English.

THANK YOU

you should never need to apologize for a language that is not your first language

niall2 · « **Reply #11 on:** July 11, 2012, 04:23:47 PM »

maybe a 12v tail light ( or other low wattage 12 v car bulb ) could be wired in series with the motor ...that should slow it down and if the power cut happens at night you,ll have some light as well ......

if you do get it to run at a slow speed you could maybe bend the fan blades to a smaller angle ( or cut them shorter ?)...this might let the motor run a little happier

Bruce S · « **Reply #12 on:** July 11, 2012, 05:26:06 PM »

Frank S; I agree

.
www.am27 : If you're going to be using the fan during power outages, and since it is a 12Vdc fan, it would be better to just connect it directly to the battery without adding a resistor or anything else.
The fan is okay to connect directly

. OKAY maybe nice clips instead of wires, but directly to battery is OK

.

If you want to slow the fan down from the high speed then a Potentiometer that can handle about 12Vdc at 4Amps can be used so any "POT" you try to use will need to handle 40watts to be safe. One that is wire wound will give you a better (smoother) slow down.
The company I work for has a small office in Pondicherry where are you located?
All the best!

Frank S · « **Reply #13 on:** July 11, 2012, 10:15:37 PM »

Quote from: Bruce S on July 11, 2012, 05:26:06 PM

Frank S; I agree .
www.am27 : If you're going to be using the fan during power outages, and since it is a 12Vdc fan, it would be better to just connect it directly to the battery without adding a resistor or anything else.
The fan is okay to connect directly . OKAY maybe nice clips instead of wires, but directly to battery is OK .

If you want to slow the fan down from the high speed then a Potentiometer that can handle about 12Vdc at 4Amps can be used so any "POT" you try to use will need to handle 40watts to be safe. One that is wire wound will give you a better (smoother) slow down.
The company I work for has a small office in Pondicherry where are you located?
All the best!

The frilight dimmer may work (FriLight d1201 Dimmers) I doesn't seem to be much more than an old rotary resister says 100 watt max, 80 wat incandescent /50 watt halogen or xenon
http://www.sailorsams.com/FriLight-d1201-Dimmers_c_695.html

www.am27 · « **Reply #14 on:** July 13, 2012, 05:25:17 AM »

Thank you guys for your replies, now i m running the fan with full speed by directly connecting it with the 12v battery. And if i want to control the rpm what should i do? I mean a dimmer will be the right choice or a potentiometer and what type?

bob g · « **Reply #15 on:** July 13, 2012, 06:39:06 AM »

if you are wanting to control the rpm to lower the drain on the battery and extend the battery life, don't use a resistor.

if you want to lower the rpm to reduce noise then go ahead and use the resistor.

when using the resistor the drain on the battery will be the same as it would be if you didn't use the resistor, so you might as well let it run without a resistor and get the most cooling you can from it for the amount of battery power you have available.

if order to lower rpm and reduce battery draw you would need some sort of electronic pulse width controller for the fan, likely hard to find there in your local city?

i am not sure, but there might be some speed controllers used on modern cars that are pulse width modulation controllers, most you will find are simple 3speed switch units that use a resistor network and mount it in the airduct to cool it and keep it from burning out.

fwiw, i would let the sucker run full speed if i couldn't locate or build a pulse width modulated controller to reduce the speed and reduce draw on the battery bank.

my opinion only

bob g

mab · « **Reply #16 on:** July 13, 2012, 05:06:46 PM »

if you can get another similar 12v fan and connect them in series, you will reduce power consumption & noise - and probably still get a good flow from your 2 fans.

www.am27 · « **Reply #17 on:** July 14, 2012, 05:12:39 AM »

Quote from: mab on July 13, 2012, 05:06:46 PM

if you can get another similar 12v fan and connect them in series, you will reduce power consumption & noise - and probably still get a good flow from your 2 fans.

I think it's not a good Idea Because this will drain my battery fast and the Backup time will decrease instead i can use some like PWM dimmer or potentiometer that can handle 12v 4A. But till now i have confusion that what should i do a potentiometer or Dimmer?

niall2 · « **Reply #18 on:** July 14, 2012, 07:07:33 PM »

erm...

i think a potentiometer will dissapate the controll current as heat ...a dimmer might be more like a pwm controll ...(more efficient ?)

if two fans are wired in series they should appear as the same load as just one ?......if the blades are tuned in to suit (running slower) .....

lots of dis- guarded battery drills have some type of pwm circuit in them ...and the internet has lots of pwm diy circuits....

whats nice about the one below is it,s based on a tl494 .....which are junked by the 1000,s every day in old pc power supplies ..........but very fiddely to re cycle

its much harder to get cheap "free ready to go" pwm modules than big resistors though ....erm ...i think ...ish

older car wind screen wiper motors seem to have a nice tough built in hard wired 2 speed geared motor

they might make a nice big slow celling 12 v air conditioning type fan .....with no speed controll needed .....as long as the battery can be quickly charged up after its needed

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Author Topic: NEED HELP (Read 5370 times)

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