kind of doubt it, he said it dimmed while he was lifting or lowering the blade. if he wasn't killing the battery when there was only 1 , he won't kill 2

 

When i add the second battery should i upgrade my alternator? I have around a 120 amp or so. I read plow motors draw 130-160 amps.

 

The key is whether or not you can let the batteries recover after draining more than the alternator can give.

Pull 150 amps from the batteries for 30 seconds, allow 60 seconds for the alternator to put out 120.

Problem is, alternators are rated at, let's say in this instance 120amps, but only at high RPMs. And, at somewhat ambient temps. Under the hood, the temps get high, so the alternator isn't going to put out it's max amperage even at high RPM.

So, tooling around at low RPMs and a hot engine, you might be putting out 40 amps from that alternator.

 

I guess this is why i ask if i should have a larger alternator to start with when you factor all the things you said above. Police cruisers get larger alternators as do ambulances, heck years ago when you ordered a diesel w/plow pkg it included a larger alt. If my current alternator is rated for my truck how can it possilby do more efficiently? I'm not buying it now but Mechman has a 250amp rated to put 165 @700rpm & 250 amp by 1700rpm. Is this worth looking into or have my local place just build me a 200amp? Will it hurt, I guess that's my question?

 

personally if you are not planning to use more juice than you used before, yhere is no need to upgrade the alternator. think about it, the original battery never went dead while you were plowing. conclusion therefore is alternator IS big enough. by putting in 2 battery you have just given the alternator a bigger tank.no wheres did I see where said anything about increasing electrical load. it probably would be a good idea to have a voltmeter so you can tell if you are keeping up, or if a problem occurs

 

I know the original battery never went dead and i never had any problems. But, call it whatever you want, i just can't stand the dimming of the lights and the defroster. I never had to see this before w/diesels and I just want to not see it now. So i'm just asking if its a good idea to upgrade the alternator to keep up with 2 batteries? If you think the alternator I have is up to the task, i'm good to go! I am very determined to solve this dimming one way or another. The second battery is going in this Sunday.

 

i think the 2nd battery should reduce it considerably. i would expect a significant improvement.

 

That dimming of the lights, and slow defroster fan, is it noticeably worse than if you turn the key on, don't start the truck, and try the lights? (when the battery is fully charged after normal driving for a while)

If it is worse, you are definitely experiencing battery drain. While a second battery will help, the alternator is just not doing enough to keep up. If the dimming starts after, say, 5 minutes of plowing, a second battery will extend that to 10 minutes (give or take, if both batteries are the same characteristics).

Starting batteries are not meant to deal with discharging too much. They are meant for high-amp short bursts of power, but not to be drained down on a regular basis.

Given your particular concerns, it sounds like a nice high-output alternator would do the trick, especially one like what you mentioned, where it's rated at a high amperage at low RPMs. Of course, that means a bigger cable from the alternator to the electrical system.

 

Dual batteries was one of the best mods I ever did for my plow. It was an 87 F250 and I mounted it on the drivers side after fabricating a bracket. Ran the positive cable across the top of the core support to connect the two batteries.

I had the stock alternator - I think it was only 60 amps and it did fine. A larger alternator would have been my next upgrade. I also kept an extra solenoid in the glove box b/c those were always the weak point!!! FYI, if you have a Meyers plow, the Ford starter solenoid is identical and considerably less-expensive than the Meyer!!

Get pics for others who may be interested!! A dual-battery set-up is something I'd like to do to my '02, but not sure where I'd fit it!!

 

my impression was that the lights dimmed momentarily, while he was actually lifting/lowering the plow. now if they are indeed slowly getting dimmer, that is another whole different thing. if they are getting dimmer over time then yes you need more output at plowing rpm.

 

While plowing. Worst at startup, then not bad until i use the plow heavy for short periods of time, under 1000rpm

 

Put in the second battery. See how it works before considering a higher output alternator.

 

if your goal is to minimize light dimming when moving the blade, the solution is a higher output alternator.
Here's why: Call it car electrics 101
The primary intended purpose of a battery is to provide electricity to start the vehicle. Once it is started, the design intent is to have the alternator provide power for everything, including re-charging the battery.

A battery puts out 12-13 volts depending on how charged it is. For this discussion, let me call it 12 volts.
An alternator should be putting out 13.5 to 14 volts. For this discussion, call it 14 volts.

14 volts into your lights means brighter than 12 volts.
If the alternator is keeping up with all demands, system voltage remains near 14 volts and the battery is either re-charging or if fully charged, doing nothing. If it can't keep up, the voltage drops down to 12 volts and you begin discharging the battery.

Is this a problem? Only if the amount the battery is discharging is more than the alternator can replace. If you are moving the blade and the lights are dimming 15 or 20 seconds every few minutes, probably not an issue. Lots of time for battery to recharge. But if they're dimmed for 15 or 20 seconds of every minute of operation, you are likely discharging more than the alternator can replace.

But if it bothers you, a bigger alternator is the answer. Even with 2 batteries, or even 20 batteries, if the alternator can't keep up the voltage will drop.

 

Exactly!!!