Which Alternator?

My alternator is shot. Like grinds when you spin it shot. So Im looking at a new one. What I have in mind is running 2 batteries, probably optimas. The reason for that is so Ill have plenty of juice for the winch. I wont have too many other electrical addons aside from a pair of KC lights in the front and maybe a couple small lights in the back. I have given some consideration to 5 KC lights mounted across the hard top with a connector so I could still take the top off easily, but im undecided on that as of yet. Im thinkin the standard 100A alternator would be hard pressed to keep up with 2 batteries. But would a 140A do the trick or would I need a 200A?

When Seabronc sees this, he will put you on the right (alt.) track.

As to "Optima" ..., I'll stand up (or down) AGAINST them. I've had 3 fail., one in my EB that has very little elect. demand. Two failed in my F-150. My 4x4'n & hot-rod build'n neighbors have had 3-4 fail between them. (I'm back to using my 8 yr.old wet-cell in the Bronco)

I talked to Optima several times & they pretty much told me to "Get in the wind"

Just say'n

B

Just a quick answer. Got to go out but, the main thing you need to know is the current draw of the extra equipment you are adding. The function of a battery is start the engine and to supply power when the engine is not running. Once the engine is running the alternator needs to be of a size that will supply the electrical demand plus be able to top off the battery/s plus. I would go for at least 25 to 50 percent more just so you are not working the alternator too hard. The battery should only be in use to start the engine and supply small loads when the vehicle is not running.

All that being said, I am guessing the one you had was a probably about a 45 amp alternator. Without knowing the extra demand, I'd say a 3G 160 amp system should be plenty. I could go into the normal use of a 2 battery system, but not in this post, not enough time.

The best source of parts that I know of for doing a complete 3G conversion is RJM Injection http://www.rjminject...ons/alternators, http://www.rjminject...tor-accessories . Read his comment , "Why he doesn't sell 200 amp alternators" , right under the big alternator picture.

As far as the battery goes, I have used the Optima and had good result. The design is cylindrical plates which are more physical shock resistant than a normal plate battery. Also there are 3 different types, so if you plan on using one, read the design usage for each, 'Yellow", "Blue", and "Red".

More later on two battery systems.

Here are a couple of previous posts on Optima


http://broncozone.co...__1#entry107650

http://www.optimabatteries.com/us/en/

Two battery systems are normally for use when camping or giving you the ability to run equipment for extended periods of time and ending up with a way to still start your vehicle. There are other uses, ie. some diesel truck engine require high starting current that a normal single battery can't supply. In the case of a recreational vehicle, you want to have an isolating relay so that when the engine is running the you have a way to charge the battery that is available for use when the vehicle is off. When the engine is off the two batteries are electrically separated by the relay. That way you don't run down the main battery.

The two attached diagrams show the two methods mentioned above. The first one you will see an aux battery relay, the output goes to the aux battery (+). from there you attach the equipment that would normally be run when the engine is not running, ie. trailer attached equipment, stereo, etc. The second one is to gain higher starting currents on a diesel.

Just a note on alternators. An alternator may be rated at 160 Amps but it does not put out that much all the time. It only puts out what the load demand is. For example, if your light bar, engine, internal equipment requires 95 Amps, then it will put out 95 Amps. If the load demand is 20 Amps then it only puts out 20 amps.

Thanks guys! Ill definately look into the 3G 160A setup. Id rather make sure my alternator can charge my batteries easily rather than workin its butt off at max output for a couple hours. As for the batteries, Im thinkin the blue top optimas (because I wont have any red or yellow in my engine bay) set up in the diesel configuration. All the extra wiring for the "isolated" battery seems a little overkill. I just want the extra power and longevity of an extra battery for winch work when the motor will be off.

OK. I forgot to include the attached diagram. So in case you change your mind bout the isolation here is a good example. Also, you could run your winch from the extra battery and just put a manual switch between the two batteries. Any way, good luck.



Just ignore the wiring for the 4.9L altitude carb control.

Seabronc, those diagrams are great! What book are they from? I only have the Haynes guide and its diagrams arnt anywhere near this clear.

Those are from a 1983 Ford Bronco EVTM (Electrical and Vacuum troubleshooting Manual). The basic stuff like that is pretty much the same over the years. I'm not sure if they have an EVTM for the 75, but you can get the factory Service Manuals from eBay. I did a search and came up with this result http://www.ebay.com/sch/i.html?_odkw=1975+Bronco+EVTM&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0&_nkw=1975+Bronco+service+manual&_sacat=0 . They have them in hard copy and on CD. They are well worth the investment. What you get is a set of manuals that cover the light truck line for a particular year. Haynes and Chiltons are a "Readers Digest" version of the real thing and they leave out a lot of stuff, like whatever they decided was not important.

I'd suggest you invest in a set of real Ford manuals.

Good luck,

Hey Seabronc, couldn't you run the setup for the diesel, but with a switch to seperate the two batteries when not charging?  Or is there something I am missing?

idman said:

Hey Seabronc, couldn't you run the setup for the diesel, but with a switch to seperate the two batteries when not charging?  Or is there something I am missing?

Click to expand...

No, you are not missing something.

What would you be running from the second battery?

A battery switch or a heavy continuous duty relay like a wheel chair 100A relay will do the same thing and cost about the same.  Also, you don't have to remember to do the switching.  You control the relay with a 12V line that is only hot when the key is in the RUN position. The one day you get lazy or forget to manually do the switching is when you run both batteries down while you are in the middle of nowhere.  A relay just makes it automatic.

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Oh, ok, I understand now.