jerrytr5 Posted February 8, 2022 Report Share Posted February 8, 2022 Fitted a replacement electric fan to the TR7 yesterday. The fan is new, but from an unknown modern. I thought the images attached were some sort of variable speed controller so didn't use the component. When I tested the fan it blew the 15A fuse, then a 20A but is ok on 25A but that seems a lot (it is through a relay and has 25A wiring before someone asks). I was wondering if this device is maybe some sort of soft-start component and maybe I should put it back in circuit. Jerry Quote Link to post Share on other sites
RobH Posted February 8, 2022 Report Share Posted February 8, 2022 (edited) Looks like a big wire-wound resistor but there is also something smaller underneath that doesn't show up well on those photos. It will get very hot hence the ceramic base. I would guess it goes in series with the motor to slow it down. Edited February 8, 2022 by RobH Quote Link to post Share on other sites
RogerH Posted February 8, 2022 Report Share Posted February 8, 2022 Hi Jerry these motors take a big current draw on start up and then settle down to a steady rate. EG - 25A on start and 5 or 10amp steady. Have you tried measuring the current after start up. I can't believe , on a modern car, that they would have that resistor in circuit all the time. Roge Quote Link to post Share on other sites
Charlie D Posted February 8, 2022 Report Share Posted February 8, 2022 Does that say "R59K" at the bottom? I would guess the green bit is just a 59K ohm resistor. But isn't 59K a high value to be in series with a 12v motor, meaning the voltage drop across the resistor would be quite high leaving not a lot for the motor. Charlie. Quote Link to post Share on other sites
RobH Posted February 8, 2022 Report Share Posted February 8, 2022 More likely R59 or 0.59 Ohms Charlie. You can see the heavy wire winding so there isn't much resistance there. I don't think the 'K' is a multiplier in this case. At 10A that would drop 5.9volts which seems feasible. Quote Link to post Share on other sites
jerrytr5 Posted February 8, 2022 Author Report Share Posted February 8, 2022 I don't think the base is ceramic, but it is a very hard plastic-like material. More photos. Quote Link to post Share on other sites
trchris Posted February 8, 2022 Report Share Posted February 8, 2022 Hi Jerry Are we talking heater fan or radiator fan? if its a heater blower this looks like a resistor to give a slower speed they are normally fitted in the input duct to the heater matrix to keep cool Chris Quote Link to post Share on other sites
RobH Posted February 8, 2022 Report Share Posted February 8, 2022 I still can't make out what that blue thing is underneath the resistor. It could be a thermal switch or fuse of some kind, or maybe even a diode. - but it looks to be in series. Probably all immaterial anyway if the fan runs OK without the resistor. It seems they are commonly used for two-speed operation e.g.: https://www.carid.com/mopar/engine-cooling-fan-resistor-mpn-68054677aa.html Quote Link to post Share on other sites
Charlie D Posted February 8, 2022 Report Share Posted February 8, 2022 1 hour ago, RobH said: You can see the heavy wire winding so there isn't much resistance there. Point taken. I looked up "ZDSA-S1" and found reference to many heater motor resistances. (and radiator fan motor ones.) http://www.ske.com.cn/2018en/products_show.asp?id=444&BigClass=Engine_Cooler_Blower_Resistor Looks to me like the component at the bottom is a diode (To stop the motor going backwards????) Charlie Quote Link to post Share on other sites
Lebro Posted February 8, 2022 Report Share Posted February 8, 2022 4 hours ago, RobH said: Looks like a big wire-wound resistor but there is also something smaller underneath that doesn't show up well on those photos. It will get very hot hence the ceramic base. I would guess it goes in series with the motor to slow it down. The small cylindrical thing underneath the resistor looks like a thermal fuse to me. Bob Quote Link to post Share on other sites
Charlie D Posted February 8, 2022 Report Share Posted February 8, 2022 I noticed on several of the items I looked at before that all I could make out were the letters “250V 10A” Putting that, along with Bob’s words “Thermal fuse”, into Google I came up with things like this. https://www.aliexpress.com/item/32743808745.html So there we go. Charlie Quote Link to post Share on other sites
jerrytr5 Posted February 8, 2022 Author Report Share Posted February 8, 2022 You boys are good. Sorry, should have said, it's the radiator fan. So the consensus is that it's basically a resistor to provide a variable (or two stage) cooling fan, which is what I originally assumed but then had second thoughts when it drew so much current. I'll check the current once it's running as Roger suggested. Cheers, Jerry Quote Link to post Share on other sites
Steves_TR6 Posted February 8, 2022 Report Share Posted February 8, 2022 Could the device be used to provide a ‘slow start’ to reduce initial current load? ie when the computer decides to start the fan it initially provides power via the resistor to reduce startup current then after a few seconds ( once the motor is spinning) the computer switches out the resistor and the fan spins up to full speed? steve Quote Link to post Share on other sites
Lebro Posted February 8, 2022 Report Share Posted February 8, 2022 What computer ? Bob Quote Link to post Share on other sites
BlueTR3A-5EKT Posted February 9, 2022 Report Share Posted February 9, 2022 21 hours ago, Lebro said: What computer ? Bob This one? Quote Link to post Share on other sites
Lebro Posted February 9, 2022 Report Share Posted February 9, 2022 Ah yes, of course Quote Link to post Share on other sites
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