Alternator: How many batteries can it take?

ajriding wrote:

Don't make the wire too fat and too short and it will limit power to reduce load on the alternator.

If you build it for maybe 60 amps with #6 wire you should be fine.

So, a thin, long wire to battery is less demanding than a thick, short one?

Other guy, how are you monitoring the alt temps? do u have a gauge?

up

A significant voltage drop along the wire will reduce the current draw.

ajriding wrote:
So, a thin, long wire to battery is less demanding than a thick, short one?

Yes a high current will cause voltage drop and slow the charging. Self limiting in a sense. Don't go too small or you will not get more than a trickle.

Don't make the wire too fat and too short and it will limit power to reduce load on the alternator.

If you build it for maybe 60 amps with #6 wire you should be fine.

So, a thin, long wire to battery is less demanding than a thick, short one?

Other guy, how are you monitoring the alt temps? do u have a gauge?

I've been surprised at my alternator lifespans, considering they have all been remanufactured lifetime warranty units from AP stores.

I've gone through several, the most recent replacement was June 2015.
and this current one is worked the hardest since, I can command 14.7v, and have very thick copper leading to my battery, but I only have the one AGM battery and my temperature data shows I am OK, unless i idle parked for prolonged periods with alternator maxed out.

Speeds under 25MPH show little difference in temperature compared to parked idling.

High output and kept cool is not going to destroy alternator, High output and hot Alternator temperatures will.

I will suggest checking out the after market hot Rod and speed shops
For heavy duty alternator

These are special build, and designed to carry full rated output

I put one in an 82 pace arrow p30 with 454
After burning OUT two auto store replacements

Standard alternator are not designed to carry full load for more than a short time
I learned that running my two house batteries low every night the expecting a good charge from the alternator was too hard on the alternator
Those batteries were under the hood, with short wiring from the isolator to the batteries

A leece Neville is not your standard Ford or GM alternator

Some alternators with internal voltage regulation might be able to protect themselves when they get too hot when feeding depleted batteries through thick cabling. Some others may not.

Don't assume yours is thermally protected against overheating, and those that are, usually contribute to the premature demise of batteries they are charging.

https://marinehowto.com/automotive-alternators-vs-deep-cycle-batteries/

ajriding wrote:
I purposely did not give details on the battery locations, distance etc because I am not looking for battery information of any sort, though it is always useful and appreciated. I'm just asking about the alternator.

Don't make the wire too fat and too short and it will limit power to reduce load on the alternator.

If you build it for maybe 60 amps with #6 wire you should be fine.

Thanks all. Matt, so you are stating that the alternator will protect itself so no worries there? I have burned out an alternator over-using it on an E350 van before, so that one did not protect itself too well. Ended up running the generator to power the battery charger to put voltage to the batteries to get home.

I purposely did not give details on the battery locations, distance etc because I am not looking for battery information of any sort, though it is always useful and appreciated. I'm just asking about the alternator.


The RV batteries actually sit in the front corner of the truck bed, they are not in the camper. I used a jumper cable as my cable/wire with proper connectors of course. I attached one end to the starter positive and put a solenoid inline and the other end to the battery positive. This is as short of a run from alternator as I could make it. The wire going to the starter is very heavy gauge. Having both banks of batteries (truck starting batteries and the RV batteries which sit in the bed) directly attached to the starter positive means possible two chances to start the engine. I can self jump with a flip of a switch (many motorhomes have this function).
The cargo trailer battery will be on a much less gauge wire, maybe 14, so will not be getting great charging, but this is typical for what a standard towed camper gets for decades and for a million camper trailers. However, the trailer battery will not get discharged much, I could probably stack some D-cell batteries together and have more than enough power….

Making use of the alternator while underway to get some amount of charging, is different than expecting the alternator to keep various distant batteries happy.

Few can expect the alternator to properly and fully recharge depleted distant batteries. Well many might expect this, but they are delusional, or misinformed or both.

Whether the alternator is overloaded by huge loads, of which a healthy depleted battery connected via thick copper circuit, can be considered, is not something one can just assume to be or not be the case.

In the marine world large banks of AGM batteries can indeed fry alternators, and some of the voltage regulators have battery temp sensors, alternator temps sensors in addition or programmable voltage settings.

Whether any particular alternator in a vehicle is going to overheat, is unknown. I sought out this information quite a while back and concluded nobody could give me anything more than a somewhat educated guess. More an issue was to figure out who might be educated so they could guess.

So, I adhered the K type thermocouple to my Stator, and have an Ammeter and can see just how hot my alternator gets at certain outputs, rpms and driving speeds. Actual data, not just an opinion. But it is applicable to my vee hickle, its alternator, and the amount of underhood airflow.

I suggest if one is indeed suspicious they might be overloading their alternator with large capacity of depleted batteries, to actualy deplete them and either aim an IR gun at the alternator and see the results, or get a 3 meter K type thermocouple to attach to their multimeter that supports temperature measurement, and a adhere it to the stator with some JB weld or some dedicated thermal epoxy.

I'm going to insulate my thermocouple from airflow as I believe that at least 15 degrees F is knocked off at highway speeds, as I also have one on my T stat housing and it reads ~180F when driving 65mph but rises to 195f when idling at a red light.