Just a general automotive question, really. I'm curious how 'smart' a modern alternator is. Do they sense a full battery and stop boiling the juice out of it or do they just keep on sending full power to your battery? Obviously, if they charge constantly, car batteries are made for this, but i'm trying to learn more about managing the 'system' i've added to my van. I have an 02 E350 with a 115 amp alternator i'm told (the Ford parts guy asked me if i had factory rear air, i said yes, and he said i've got a 115 amp alternator if it's never been altered). Anyway, i've added a voltage sensing relay (a dual battery isolator, basically) and i've added 2 marine batteries to the back to run an inverter for AC fridge, micro, and other camping needs. I'm trying to get a better handle on how long it will take my van to recharge these when depleted using the alternator, and whether not the alternator just keeps boiling them or sort of idles down once your battery is charged.
I do know that at idle, my alternator is putting out about 13.9 volts, so it is charging at idle, but i've always been curious how this changes at higher rpm (while driving), and whether not it 'floats' once the batteries are charged.

thanks

 

Once upon a time there was an inner fender mounted voltage regulator that through magnetic switches directed generated voltage to the ignition/electrical system or to ground depending on the load called for by the vehicle. When alternators replaced generators internal solid state voltage regulators did this same chore. If a voltage regulator "sticks" in the full juice to batteries you'd eventually fry them but for the most part they're reliable enough this is somewhat rare.

The battery will basically take what it needs until fully charged then "backfeed" the alternator/regulator in a way that voltage is directed to ground. It does "float" between charging and not charging based almost exclusively on the battery's condition.

If I'm correct the VSR's will charge auxiliary batteries only when they "see" incoming voltage higher than they're storing at the moment? Used as or in place of an automatic isolator to prevent draining the main starting battery? Is it possible or desirable to install battery condition gauges, switchable to monitor them during driving or running your fridge etc?

 

JWA, thanks! I've been doing some reading and also posted this same question on a couple of RV forums and got a lot of info back i'm still trying to read. I think i'm ok without extra guages. My setup is working well so far, i was just trying to gather what an alternator actually does and when. I didn't think it could possible keep juicing the batteries but i wasn't sure. From what you've said and what i've read, it basically floats once charged. The VSR does the same when you add batteries. It has an LED on it which tells you when it has 'cut in' or 'cut out', depending on current voltage at the truck battery. It only sends juice to charge house batteries when the main battery is sitting at full charge, and it won't allow you to drain down your truck battery if you drain down the house batteries while sitting. So far, it's working perfect.

 

After the video I saw on Ford alternators, I found out the Windstar alternator puts out 135amps.
I would only have to "Clock" the case to make it work in my E350.

 

To what advantage? The stock typical Ford-installed alternator has 130 amp output---that can be increased quite considerably if its necessary or desirable to do so. If not used on a RV or heavy work truck the stock output works for most owners.

 

I ran the OEM 110 alternator on my E350 diesel for years. I had this brilliant idea of installing a used 130 amp alternator from a wrecked E350 and it started acting up on a 10,000-mile road trip. My regular diesel mechanic persuaded against it as I am asking for trouble with an unknown product.

Long story short, I ordered a 130 Amp alternator from Bosch from Amazon and had it delivered to my stopover in Arkansas.

My 110 stock alternator was charging 4 AGM batteries on the diesel. I run a battery isolator between the 2 banks of 4 batteries.

As JWA mentioned, the alternator provides whatever the batteries need. It may take longer, but it still gets the job done.

I removed a rebuilt alternator from my gas E350 this morning as it failed. I could tell it was remanufactured because of the poor paint job. I bet my 110 amp Motorcraft alternator that still works has over 800,000 miles on it. The van has 822,000 miles.

Keep your van stock unless you know what you are doing.

 

Mahalo nunui (Thank You Very VERY Much) for the heads up!!!
I'll probably go with an isolator though...so far she's better since I
rewired the starter which was done by Diesel Mechanics by Dummiez!!!!
Aloha Every Minute,
Chief

 

Quick question: should I add in a battery cut out switch for the rear battery???
Mahalo Nunui for your time!!!
Chief

 

It couldn't hurt A heavy duty car amp fuse would be a good idea too. Just in case.

 

Mom's 15 Passenger 1997 E350 4X4 445cid Powerstroke Diesel Club Wagon.
Work in progress.
TLC Mechanic Special.
A Cowboy's Work Ain't Never Done...
Van named: "Bessie"
Aloha Every Minute!!!
Chief

 

@86scotty When my Mom bought Bessie II I was having serious discharge issues even after the new Alternator & Batteries install...only to find out Diesel by Dummiez had thought this van had 24v start. I went online & found out they were wrong & it was Hi Amp 12v Paralell..They tried using the solenoid/glow plug ecm like it was a series/parallel switch. I finally went in & undid Diesel by Dummiez and fixed the problem. Bessie holds juice...but the starter gotta go... I got the starter wired solenoid to solenoid like my old gas burner "Bessie I." She cranks up no problem & there's NO Power Drain.Mine is a Napa Rebuilt Alternator rated @ 130amps.
Aloha Every Minute,
Chief

 

Unfortunately, 86 Scotty hasn't been on the forum snce 2017.

 

Didn't know that, but I hope others will see my post & avoid "Diesel by Dummiez…"
Hopefully 86Scotty will be back.
Aloha Evert Minute,
Chief

 

@Spaznaut I might go with a Caterpillar On/Off Switch or the Battery Shutoff with the key.
Don't know yet..
Aloha Every Minute,
Chief

 

I installed the new rebuilt Ford 130 amp alternator this afternoon. I bought the alternator for AutoNation White Bear Lake for about $180 including shipping and core charge.