martyn wright Posted September 8 Report Share Posted September 8 (edited) Hi! One quick question! My next door neighbour was looking at my car on the drive and asked if when I had the positive dynomo, changed to negative by fitting a new Alternator did I change the wire's over on the Heater motor? It runs fine?He said that it would suck instead of blow? Is this correct? Edited September 8 by martyn wright Link to comment Share on other sites More sharing options...
johny Posted September 8 Report Share Posted September 8 well its a centrifugal fan so whichever way it rotates air will tend to be flung outwards so the direction of flow will be the same ie into the car. However if running backwards its efficiency will be less although with a these units that may be difficult to tell😁 Link to comment Share on other sites More sharing options...
foshi Posted September 8 Report Share Posted September 8 will be fine Link to comment Share on other sites More sharing options...
martyn wright Posted September 8 Author Report Share Posted September 8 Thanks guys! 😊 Link to comment Share on other sites More sharing options...
Wagger Posted September 8 Report Share Posted September 8 If a DC motor has a wound field and armature, then it will rotate the same way if you swap the polarity. You have to reverse the field winding or armature brushes if you want it to reverse. If it has a permanent magnet for the field, then it will reverse if you swap the polarity. Corded power drill braces used a series wound DC motor that will run on AC because both windings are swapping polarity fifty times per second. Link to comment Share on other sites More sharing options...
Colin Lindsay Posted September 8 Report Share Posted September 8 I'd say immediately: NO! DO NOT CHANGE OVER ANYTHING! I suspect the heater will continue to spin in the usual direction regardless of which way the polarity is, but the reason I'm very emphatic on this is because the next step in what may be an Old Wive's Tale is the wiper motor. Many many years ago on my Herald Estate restoration I read that if you change polarity you need to change over the heater blower AND the wipers, as the latter will have been running in one direction for many years and will have bedded in. If it runs in the other direction it will wear more quickly and be noisier in operation. Another source of information on the subject stated to see which direction was better and quieter, so swap over the motor connections and if they're noisy, swap them back. What harm can it do to check? Well, the wiper motor circuit is permanently live as it has the park function which is independent of the switch. To prevent any chance of the wires being incorrectly attached to the motor the live terminal has a fin that fits into a slot on the motor casing. This has to be cut off to swap the wires around. So, taking advice from those who I believed should know better, I cut off the fin and swapped the wires around. The brand new Autosparks loom promptly melted in clouds of smoke. The heater motor may be a different kettle of fish, being wired more traditionally, but please research very thoroughly if it's required before trying any circuit reversal. The alternative is a few hundred pounds of replacement loom! Link to comment Share on other sites More sharing options...
Josef Posted September 8 Report Share Posted September 8 The heater motors on the Herald / Vitesse are of the wound field armature type that Wagger mentions. So are the Lucas DR3 square body type wiper motors. Source, me deliberately trying to reverse the direction of an otherwise scrap heater motor and having to re wire it internally! So you don’t need to touch anything. By the time fixed magnets were good enough that they were viable in automotive equipment (in Triumphs at least) the standard for negative earth had also arrived. 1 Link to comment Share on other sites More sharing options...
martyn wright Posted September 10 Author Report Share Posted September 10 Thanks guys! 😊 Well both are working fine with no problems so I ain't touching them! Link to comment Share on other sites More sharing options...
Wagger Posted September 10 Report Share Posted September 10 Even though I am an Electrical guy, I am still mystified as to why ignition coils have to be reversed. I understand all of the rest having spent two years of day release doing electric motor theory. Fleming's left and right hand rules, the corkscrew rule for current through a wire etc. So long as you adopt conventional current flow and not electron flow. YES! electrons flow from negative to positive but we discovered this far to late to adopt it. Lecturers then tried to use 'Hole' current, confusing 90% of the students altogether. Link to comment Share on other sites More sharing options...
johny Posted September 10 Report Share Posted September 10 You must have seen how coils are wired inside though Wagger? I didnt realise that the two coils are connected at the positive terminal - not as I expected kept electrically separate like a transformer.... Link to comment Share on other sites More sharing options...
johny Posted September 13 Report Share Posted September 13 Thinking about it a strange design as the spark current must return to the coil through the block to the earth of the dynamo/alternator and back through it and the system via the ignition switch to the coil positive terminal! Then before the spark is generated the dizzy rotor arm must sit at 12v all the time the ignition is on🤔Additionally I always thought the coil case needed to be well earthed and thats obviously not right - theres something new everyday.... Link to comment Share on other sites More sharing options...
Wagger Posted September 13 Report Share Posted September 13 2 hours ago, johny said: Thinking about it a strange design as the spark current must return to the coil through the block to the earth of the dynamo/alternator and back through it and the system via the ignition switch to the coil positive terminal! Then before the spark is generated the dizzy rotor arm must sit at 12v all the time the ignition is on🤔Additionally I always thought the coil case needed to be well earthed and thats obviously not right - theres something new everyday.... Thanks Johny. I should have looked it up. That is the problem with being qualified in electrics. One can assume that you remember everything. Not quite, eh! Neighbours laugh at me, I am the only Electrical guy in the street and I have no outside light or camera. I do things for others and not for me. Maybe it is because I do not pay myself eh! Link to comment Share on other sites More sharing options...
Colin Lindsay Posted September 13 Report Share Posted September 13 49 minutes ago, Wagger said: Neighbours laugh at me, I am the only Electrical guy in the street Torchy the Battery boy? But then you say you don't charge.... Link to comment Share on other sites More sharing options...
Wagger Posted September 13 Report Share Posted September 13 5 hours ago, Colin Lindsay said: Torchy the Battery boy? But then you say you don't charge.... Not done much in recent years, but I was usually paid by being fed. No incentive to do electrical work for me unless it is on my vehicles. House stuff seems to work ok so I leave it alone except when when storms and toasters cause tripping. Then, it's reset everything that has tired backup batteries. Must try harder I guess. Link to comment Share on other sites More sharing options...
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