Happy then disappointed…

[Tony 69]

Today I finally got my front disc power brake conversion completed on the 69 bird. So exciting and they work great! Then I drove to my dad’s house to put the bagger on the mower for leaf season. I was ready to leave and go find a mustang or something to embarrass but no start. Just clicking. So I got a jump and came home. The alternator has to be working or I wouldn’t have made it home. The question is….if I have a 35-38 amp alternator and the electric fan I added draws 20 amps, why is my charging system not keeping up? I’ve cleaned and checked all connections and did the ammeter bypass. I don’t get it and mostly, just disappointed.

 

[Aron Gleason]

I would think a 60 amp alternator would work better for you. Did you run a relay for the electric fan?

 

[Tony 69]

No I just put it on a switch
But let’s say 35-20= 15
I guess it doesn’t work that way

 

[Gus chiggins]

I would think a 60 amp alternator would work better for you. Did you run a relay for the electric fan?

Relays are everyone's friend.

 

[Tony 69]

I get it, an external switch that you do not control. But the amp draw should be the same either thru a relay or switch. Shouldn’t it?

 

[Aron Gleason]

I get it, an external switch that you do not control. But the amp draw should be the same either thru a relay or switch. Shouldn’t it?

Not so. A relay will drop the amperage where a switch is only rated for the amps thats going through it. Without a relay you run the risk of melting the toggle switch and burning the wires and everything else.

 

[Tony 69]

I’m sure I follow you on this. And that’s why I posted so don’t be offended. The current or amp draw is the same. The switch is rated for 30 amps and has a fuse on the power side so things won’t get melted or any of that. You also use a fuse in the circuit when using a relay. So what is the difference?

 

[Gus chiggins]

I’m sure I follow you on this. And that’s why I posted so don’t be offended. The current or amp draw is the same. The switch is rated for 30 amps and has a fuse on the power side so things won’t get melted or any of that. You also use a fuse in the circuit when using a relay. So what is the difference?

Oh well, a relay is always there, no worries about throwing a switch.

 

[motime]

The fan motor will draw the same amperage if controlled through a relay or switch. Their both contacts. Switch manually controlled, relay automatically controlled. More alternator output should help.

 

[PlymCrazy]

No I just put it on a switch
But let’s say 35-20= 15
I guess it doesn’t work that way

With the electric fans in there I’m thinking you’re going to need a bigger alternator. That 15 amps leftover in your equation would be needed to cover the remaining electrical components running on the vehicle i.e. ignition, lights, radio, etc.

Also any mechanical to electrical conversions that may have been done on the car, differing from original, would impact that current draw.

Here’s a good tool for determining alternator size when you start adding to your electrical system like fans and such…

https://powermastermotorsports.com/tech/How to Choose a Hot Rod Alternator.pdf

 

[kiwigtx]

Not so. A relay will drop the amperage where a switch is only rated for the amps thats going through it. Without a relay you run the risk of melting the toggle switch and burning the wires and everything else.

Spoken like a Plumber.

Sorry, but with respect I have to disagree....no red X.....

*******************
A relay cannot drop the 'amperage' (not even sure if that's a real word yet). A relay is a device used to divert the 'current' away from the switching mechanism, directly to the load. (fan in this case)

A switch typically is used for switching the relay coil, which consumes a fraction of the current of the of the load being controlled.

A switch can be used for switching the load directly, but the switch contacts must be rated for the appropriate load, and voltage as well as number of operations it will be used to switch the load.

A fuse is the device used to prevent to break the circuit in the case of an overload of current to the load.

The fuse does not control the current flow - it is only there as a safety device to cut the circuit.

Current flow if controlled by either a limiting resistor, or the load itself. However, if the load (fan in this case) becomes compromised by a short circuit, then control is lost, and the current increases dramatically, and rapidly, and this is where the fuse operates.

Electrical work is not easy, and caution should be exercised by those who are not sure of what they are doing. It frightens me sometimes when I see guys installing their own electrical mains supplies and distribution panels at home here.


BTW, I am not the expert, I am sure others will want to add their 5 cents worth. I'm just an ordinary Electrician with 40+ years under my belt.

 

[RemCharger]

'amperage' (not even sure if that's a real word yet).

Hmmmm.. there must be more to the story??

 

[Lefty71]

Spoken like a Plumber.

A small switch can get the power to a large relay, and turn on large loads that way. In my mind relays provide for cost savings in WIRE AND SWITCHES, especially in remote loads. Their use has very little to do with overall power used. Take it from a plumber lol.

 

[Don Frelier]

Back to the original question:
Here's a good case for watching your ammeter.
If it's always towards discharge then yes your battery will lose its charge.
But since you bypassed the ammeter now your flying blind and wondering what's going on.

 

[HawkRod]

Remember also that a 35 AMP alternator can only supply that power when it is rotating fast enough. At idle, it can't even run headlights well enough so they stay bright, so a 20 amp fan will kill your battery during any idle or slow engine speed situation.

Your solution is still to use a bigger alternator, but you need to know what you are doing. The Mopar "Packard" spade connections (e.g. where your wiring harness goes through your firewall) can only handle about 35 amps. If you are going to be putting more power through the system you need bigger wires and better connections. Don't just throw a bigger alternator on your car - be sure you know and understand what you are doing.

 

[Geoff 2]

The rated alt output [ say, 50 amps ] is not at idle. It is less. So your battery might be discharging at idle & low rpms [ which is when you are using the elec fan ] because you are drawing more current from the battery than the alt can output. Fixes:
- smaller alt pulley
- bigger alt
- different design alt that has higher output at lower rpms

 

[Tony 69]

Thanks for all the suggestions. I was concearned a higher amp alternator would need a larger size wire. I may try a smaller pulley first. Anyone know where to get one?

 

[Demonic]

An alt with a higher amperage rating does NOT change the amperage demand of a given vehicle. Say your 69 car uses 20 amp for the fan, 5 for ignition, another 10 for the lights at night, another 10 for the Craig AM/FM under the dash. Add another 5 for misc. Car uses 50 amps. If you add 100 amp alternator versus a 60 amp unit the car still uses 50 amps.

I've had bad new battery cables give a 'no start' that caused me to need a jump. What is your voltage at the battery at idle and 2000 rpm?

 

[HawkRod]

An alt with a higher amperage rating does NOT change the amperage demand of a given vehicle. Say your 69 car uses 20 amp for the fan, 5 for ignition, another 10 for the lights at night, another 10 for the Craig AM/FM under the dash. Add another 5 for misc. Car uses 50 amps. If you add 100 amp alternator versus a 60 amp unit the car still uses 50 amps.

Absolutely 100% agree.

Note that the OP has added a fan that draws 20 Amps, so he has increased the electrical demand of the system considerably. If he adds a high power alternator, it will start feeding that increased demand through the stock wiring. Will it be OK? As I'm sure you know, it depends on a lot of factors, including how he wired in the fan. My point to the OP was and still is that he should be sure to understand what he is messing with. The original design of our wiring systems was marginal, so they don't do well handling more power demands from modern add-ons.

 

[Davefinan]

Spoken like a Plumber.

Sorry, but with respect I have to disagree....no red X.....

*******************
A relay cannot drop the 'amperage' (not even sure if that's a real word yet). A relay is a device used to divert the 'current' away from the switching mechanism, directly to the load. (fan in this case)

A switch typically is used for switching the relay coil, which consumes a fraction of the current of the of the load being controlled.

A switch can be used for switching the load directly, but the switch contacts must be rated for the appropriate load, and voltage as well as number of operations it will be used to switch the load.

A fuse is the device used to prevent to break the circuit in the case of an overload of current to the load.

The fuse does not control the current flow - it is only there as a safety device to cut the circuit.

Current flow if controlled by either a limiting resistor, or the load itself. However, if the load (fan in this case) becomes compromised by a short circuit, then control is lost, and the current increases dramatically, and rapidly, and this is where the fuse operates.

Electrical work is not easy, and caution should be exercised by those who are not sure of what they are doing. It frightens me sometimes when I see guys installing their own electrical mains supplies and distribution panels at home here.


BTW, I am not the expert, I am sure others will want to add their 5 cents worth. I'm just an ordinary Electrician with 40+ years under my belt.

I was an electrician for 40 plus years also…..also no expert.
Amperage is definitely a real word , but I suspect you must know that.