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22A fan motor turn on question
2

22A fan motor turn on question

22A fan motor turn on question

(OP)
I have a 2-fan radiator cooler. At idle it draws 22A, or 11A each fan. Each fan is on its own relay. But the relays are turned on-off simultaneously. Should I turn the fans staggered to reduce transient? I have no idea how much is excessive motor current. Thank you.

RE: 22A fan motor turn on question

That depends entirely on whether the vehicle's electrical system can handle the current including the momentary starting current.

If it is an old-school hard-wired relay circuit with the main power coming through a fusebox and the wiring is adequately sized for the current and the battery is good and the various connections in the system are good (adequately sized and not corroded) and the battery is big enough and in good shape and it's not blowing the fuse ... good enough.

If you have undersized wiring and bad connectors (as evidenced by significant voltage drop between the battery and the fan motor) you're going to have a problem and possibly a fire.

Follow the traditional troubleshooting chart. "Does it work" - "Yes" - "Leave it alone" - "Done".

RE: 22A fan motor turn on question

Definitely stagger the start if you can and it is easy. I'd expect a surge current of anything up to 300% steady state, but probably less knowing most automotive wiring.

If it isn't easy then what problem are you trying to cure? 60A for a second or so won't hurt your battery .

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 22A fan motor turn on question

(OP)
Sorry I didn't tell you all. There is no issue. Healthy battery, 10 gauge wires. I already have a 3-relay setup to start with serial and switch to parallel. But for simplicity, I start fans only in parallel configuration (one less wire😀). I am about to solder and pour epoxy to my experimental arduino controller and wanted to ask the question to an expert before actually doing it. If you recommend serial start for healthy electrical system, I can easily implement it.

RE: 22A fan motor turn on question

If it's easy, and with an arduino it is dead easy, then do it. Less stress is always good. For extra points you might set the fan on temperature for the two to different levels, that way if you only need one fan you'll get just that, and they'll naturally sequence themselves. For extra points switch them on first alternately to even the lifetime of the motors out. My experience is that unless you are towing full fan power is rarely required.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 22A fan motor turn on question

First rule of maintenance: things that aren't broken, don't need mending!

RE: 22A fan motor turn on question

(OP)
Haha, I broke the system😀. I removed the oem clutch fan and put an electric fan.

Thank you G.L. Will do.

RE: 22A fan motor turn on question

Your two fans are gobbling up 270Watts of power. That's 0.35hp.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 22A fan motor turn on question

(OP)
Yes, I know that. My question was if I had better stagger the fan motors to reduce inrush current and the answer from the experts was yes if easily implementable.

RE: 22A fan motor turn on question

Starting in series will greatly reduce the inrush current stresses and you have the relays wired and a controller that could do it. So, why not?

Still, if you are using an Arduino then why not do PWM fan control? It eliminates all inrush surging. It eliminate the mechanical relay as a possible source of failure. It provides near constant temperature control vs having the temperature swing as the fan goes on and off. It makes the system quieter since full fan speed is rarely required. Lots of wins with PWM.

RE: 22A fan motor turn on question

(OP)
Why not PWM? Because I am not EEsad. I can drive a power mosfet with arduino but don't know how to build protection from power spikes. Commercial products sold to hobbyists don't have a good rating. I just don't trust their engineering. I also thought about adopting oem power mosfet module (fan controller) and driving it with a transistor switch as ECM does. Again I don't know how to protect the transistor switch from power spikes.

The Arduino controller + relay is safe from power spikes (I hope). A buck converter sits between Arduino and battery. A 5V relay sits between Arduino and the 12V car relay.

If you have other thoughts, please let me know.

RE: 22A fan motor turn on question

Once upon a time I worked on a twin fan PWM installation. It was very interesting, most of the time the fans were off, and even when they were on they spent a lot of time just ticking over at 10%. One nice thing I did was to avoid certain speeds that were noisy due to resonances. Sadly it didn't make it to production. Fear not- it's one line of code https://www.arduino.cc/en/Tutorial/PWM, but you will need to drive each fan through an FET which is typically more expensive than a relay say https://www.ebay.com.au/itm/3V-5V-Low-Control-High... (I hope $6 doesn't blow your budget). Lionel's idea of starting them in series and then flicking over to parallel is a neat alternative but will probably cost more than the FETs.

Of course if you want to have a bet each way use a relay to switch one to full power, and control the other one using PWM/FET . That could get very bizarre, you'd need to latch the relay on otherwise it'll cycle rapidly in some conditions.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 22A fan motor turn on question

(OP)
G.L.
I read somewhere those drivers without power spike protection are bound to fail. Being non-EE I got scared. Because of your recommendation, I will try PWM. One question though. The description says heat sink for greater than 5A. How do I attach a heat sink? Looks impossible. Do they come with HS premounted? I couldn't find one

RE: 22A fan motor turn on question

wander into your local electronics store and they'll show you. Basically you stick them to the chip with the right sort of glue. I daresay you might find the right sort of thing on the cpu of a broken computer.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: 22A fan motor turn on question

(OP)
The heat sink side is already soldered to the board. So attach a heat sink to the other side? Sorry for asking this foolish question.

RE: 22A fan motor turn on question

(OP)
The mosfet is placed on the board horizontally with the HS side down. There is no gap between the FET and pcb. I think the metal heal sink is soldered to the board.

RE: 22A fan motor turn on question

Perhaps he's talking about the component body's flag (exposed die metal slug, normally used for extra heat dissipation)... not a "heat sink" side, per se. If so, that part is designed to be soldered to the PCB. A heatsink would sit on the other side and use some grease. to make contact.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: 22A fan motor turn on question

(OP)
Ok, now I understand. Let me ask another foolish question. Since it's so small and cheap, can I put 2 in parallel for improved reliability?

RE: 22A fan motor turn on question

For protection, put a reversed biased diode across the motor to handle any inductive spikes and a a MOV across the FET to help protect it from over voltages.

I've seen similar modules with TO220 devices so you could attach a heatsink to the tab. Find a similar device with a higher current rating if the device the board comes with isn't rated for enough current.

You can parallel FET's, but you have to be careful to keep the lead lengths and lead inductance the same going to each FET. I suppose if you parallel those boards then split the large gauge power and ground wires to a smaller gauge and use same length of wire from the split to each board. Try to keep the wires routed similarly too.

The most likely failure of that FET board is a shorted FET so I don't see you gaining much for reliability by paralleling them.

RE: 22A fan motor turn on question

(OP)
Thank you for the explanation. I think I am ready to experiment with PWM and FET for the first time. smile

RE: 22A fan motor turn on question

The reason for staggered start is to not use more cooling than is needed. As long as one fan is enough, you don't need the second fan so why bother to run it?
Use a two step thermostat to start one fan and, when needed, the second fan.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 22A fan motor turn on question

If you do go the PWM route, you still need to stagger the start times to avoid a huge inrush current.

Dan - Owner
http://www.Hi-TecDesigns.com

RE: 22A fan motor turn on question

(OP)
Thank you for the notes. Will follow your suggestions.

I have a related question. I have not seen a flyback diode on any radiator fan motor. Is there a good reason?

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