Alternator field wire - is the current draw continuous?

[lndwarrior]

I am trying to summarize my continuous vs. intermittent electrical loads. As near as I can figure the field wire circuit draws between 2 and 4 amps.

I would like to know if the alternator field wire current is a continuous load - or a intermittent load that drops off once the engine/alternator are running?

TIA
Gary

[RVDan]

Consider the field current at its max as a continuous current (because it is). Most 12V alternators have about a 4A field current at max alternator output. Some of the 70A alternators might take 5A.

[bkthomps]

and i've learned that if the field wire pops, you are likely hitting the "over voltage circuit" on the B&C regulators

my culprit is the cessna style master switch, which over time ~500hrs or so, they get internally corroded and cause false alarms

[lr172]

The field has a relatively linear power draw based upon current demanded from the alternator. The regulator will keep feeding more current on the field (forcing the alt to produce more current) until the voltage reaches it's set point or alternator reaches it's maximum capacity. i.e. the field current increases with the alternator output. Max draw will vary on both the alternator and regulator design. My 50A alternator would trip the 5A breaker at loads over 40 amps. Unsure if it was truly drawing 5 amps or if my breaker was tripping early. I replaced with a 7.5A breaker.

As I learned, you need to size for continuous use at full draw. If you ever run your battery down, you will run at max capacity for a period of time long enough to trip the breaker. Not something you want to learn "in the air" as I did.

Larry

[lndwarrior]

Thanks for the detailed replies.

I appreciate it!
Gary

[Kahuna]

You may also have a self exciting alternator. Many of the automotive alternators, particularly chevy, have this feature. Once up to an rpm, off it goes on its own and killing any field wire you may have to get it going, does nothing after it is. You can kill the field and it will keep on charging.

[lr172]

Originally Posted by Kahuna

You may also have a self exciting alternator. Many of the automotive alternators, particularly chevy, have this feature. Once up to an rpm, off it goes on its own and killing any field wire you may have to get it going, does nothing after it is. You can kill the field and it will keep on charging.

Kahuna,

Very few internally regulated auto alternators have a field connection. There is a field circuit, but you usually have to cut them open to get access to the field circuit. some leave an opening in the case for a technician to get a test lead on them. Some atlernators, separate the B lead, or output, from the Excitation feed (most contemporary alternators are single input). The excitation feed is typically just input power/voltage sense for the regulator and is not a field lead. It essentially creates on on/off situation for the voltage regulator. Those with separate excitation inputs will typically not produce output without voltage on this lead. In the case of single input, the excitation is bridged internally and they cannot be prevented from producing power.

Larry

[TomDPilot]

Have an RV6A with a Duralast 14184 alternator that needs to be replaced. This alternator was used in late 70s and early 80s Hondas and a replacement is not "off the shelf" taking several days to arrive. Anyone have any alternatives for an alternator that may have a more recent application?

[moosepileit]

Had same issue with the 14129.

Snagged one online, will rebuild the other for education.

Looking at switching to an IR model and adding OVP to it.

[lr172]

Originally Posted by TomDPilot

Have an RV6A with a Duralast 14184 alternator that needs to be replaced. This alternator was used in late 70s and early 80s Hondas and a replacement is not "off the shelf" taking several days to arrive. Anyone have any alternatives for an alternator that may have a more recent application?

I use a 14158; same era as yours. Can find them on amazon with one day delivery or local auto parts store sometimes. 50 amps externally regulated and CC rotation to match our engines.

Larry