Need Education re relays and elect flow

sprice

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There is a recent post on ammeter bypass i have watched and read Daniel Sterns article on relays. I understand the wiring concept however get lost in the flow, and maybe that's wrong. I have a 68' 300 with an electric fan with two relays powered directly from the battery with a temp switch turning on/off. If the fan is drawing say 30 amps when on from the battery, is the replacement power not still flowing through the ammeter if no changes made from alt to firewall to ammeter to battery? How do the relays reduce the flow through the ammeter? Same example would be with a headlight relay. I guess the question is, if power taken directly from battery by other sources, how does that reduce power replacement through the ammeter?
 
Your replacement power for the fans is still flowing through your amp meter , get ready for a electrical fire at the back of your amp meter. The possibility of fire grows with the use of any factory electrical options (heater fan , lights ) that are used at the same time as the rad fan A head light relay works by reducing the flow of power through your headlight switch and taking the power directly from the battery so your headlight switch doesn’t heat up and burn out .
 
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A relay uses a lesser-draw circuit to control a larger-draw circuit. Which reduces the current draw through the original circuit and all that might entail. Which also means that full battery voltage gets to run those circuits rather than a reduced amount. Which is why relay-controlled headlights are brighter than headlights controlled via the OEM circuit, for example. The charging circuit should still see the same amount of voltage regulator-controlled load, which is why the flow through the Ammeter would not change, as I understand it.

In the case of hvac fan motors, when on "High" speed, they are usually getting full battery voltage rather than going through the various levels of blower motor resistors to make the lower fan speeds. No long-term issues when used exclusively on the lower speeds, but on "High", some fan switches can melt/fail with extended "High" blower speed use (which many in the Southwest USA might use in the hotter months). I recall some Chevy Astro van OEM fan switches that might fail every 18 months or so in normal use in TX, for example. One customer had had to replace THREE such switches. One side issue in these particular failures might have been that the a/c system(s) were a bit undersized resulting in the fans being uses on "High" for extended periods rather than having enough capacity to allow lower speed settings after the initial cool-down? OR the switches were sourced from a vendor that was less expensive, although with a somewhat higher ultimate failure rate? OR, also, not enough ambient air flow to sufficiently cool the switch? By observation, the ambient atmospheric cooling helps keep headlight wiring connectors (at the headlights and taillights) from getting too hot.

Just some thoughts, experiences, and observations,
CBODY67
 
There is a recent post on ammeter bypass i have watched and read Daniel Sterns article on relays. I understand the wiring concept however get lost in the flow, and maybe that's wrong. I have a 68' 300 with an electric fan with two relays powered directly from the battery with a temp switch turning on/off. If the fan is drawing say 30 amps when on from the battery, is the replacement power not still flowing through the ammeter if no changes made from alt to firewall to ammeter to battery? How do the relays reduce the flow through the ammeter? Same example would be with a headlight relay. I guess the question is, if power taken directly from battery by other sources, how does that reduce power replacement through the ammeter?
If fans 30 amperage draw is from the battery and the amperage to recharge the battery runs from the alternator through the ammeter and to the battery, it seems the charging system would make up for the used amperage with higher alternator output. Otherwise the battery would not stay fully charged.

Thus I don't believe that your relays are doing anything to reduce amperage through the amperage meter. I agree with @Welder guy that the ammeter bypass is a very good idea for your car.
 
There is a recent post on ammeter bypass i have watched and read Daniel Sterns article on relays. I understand the wiring concept however get lost in the flow, and maybe that's wrong. I have a 68' 300 with an electric fan with two relays powered directly from the battery with a temp switch turning on/off. If the fan is drawing say 30 amps when on from the battery, is the replacement power not still flowing through the ammeter if no changes made from alt to firewall to ammeter to battery? How do the relays reduce the flow through the ammeter? Same example would be with a headlight relay. I guess the question is, if power taken directly from battery by other sources, how does that reduce power replacement through the ammeter?
First, glad to see the correct term "ammeter".

Let's understand (although I think you do), that the relays for the headlights are added to reduce the current running through the connections at the bulkhead, switch etc. and to have less voltage drop because of shorter, more direct wiring. Using a relay for the fan is done so any additional wiring (let's say a dash switch) also has less current running through it.

Let's forget about the fans for a minute.

So, in answer to your question, yes, the charging current is still running through the ammeter. Adding headlight relays keeps the current down running through the wiring, and that's good, but it doesn't change what runs through the ammeter. But that current also hasn't increased, and as long as everything is in good condition and tight, all is good.

Now add the fans. Yes, the amount of current draw from the battery is increased. The battery will now need more charging current, but you have some limitations. One is alternator output. It's only going to charge what it can. So, in theory, all should be good, but it is going to be taxed. But will the stock, low output alternator be enough? Probably not. So you put the higher output alternator on that's capable of charging the battery a little faster and now you are pushing the stock wiring and ammeter past its limitations.

If you are adding fans, yes, good idea to do the bypass. Adding fans AND increasing alternator output to make up for them? Yes, do the bypass, no question. Adding just a larger alternator with nothing else? Yes, good idea to do the bypass, but remember that it only puts out what it needs to (I had a girlfriend like that once) and unless you've added more draw (like amplifiers or fan) it's not charging any more than your stock alternator did.

It is my opinion that the so called ammeter fires are actually bad wiring or loose connections (especially at the ammeter). Doing the bypass is still a good idea for many reasons though even when staying stock. It does take the load off the wiring and connections.
 
Thanks to all. Makes sense now. I did upgrade the Alt. to 60 amp and wiring to 10 ga. Separated the ammeter wiring from the bulkhead connector to h its own connection. Appears to operating good like it should. Needle moves about half way on charge side of the ammeter when fans are on. However, to be on the safe side, ammeter bypass will be added.
 
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