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22A fan motor turn on question 2

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knowlittle

knowlittle

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Jul 26, 2007
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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.

 
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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".
 
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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
 
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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.
 
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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
 
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First rule of maintenance: things that aren't broken, don't need mending!
 
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Haha, I broke the system😀. I removed the oem clutch fan and put an electric fan.

Thank you G.L. Will do.
 
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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.
 
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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.

 
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Why not PWM? Because I am not EE[sad]. 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.

 
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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 but you will need to drive each fan through an FET which is typically more expensive than a relay say (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
 
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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
 
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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
 
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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.
 
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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.
 
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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
Footwell%20Animation%20Tiny.gif
 
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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?
 
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