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It is a device turned by the engine via a serpentine belt that under ideal conditions can produce 180 amps of electricity at about 14.3 volts which is then turned into direct current. It charges your starting battery and runs the myriad of other loads put on the battery by the vehicle. There is an optional one that can produce up to 225 amps but you don't need it for your gasser. Is that enough answer?
 

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To do what? I have a 225 amp one in my diesel. It has been tied to my 215 A-H storage battery a few times when that battery was about 40+% discharged. The connection is fused at 80 amps. The fuse has never blown. So for that use <80 amps. The alternator can output more current than that BUT I don’t want more going to my batteries. Internal resistance in batteries tends to control the charging rate. Lead batteries have this wonderful property.
 

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How many amps can you expect under normal driving conditions? Not at 6000 rpm
I'm interested in this too, as well as what you might expect from the standard alternator at idle.

Aside from optionally charging house batteries, I may run some DC loads directly only while the engine is running.
 

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As I posted a while back, I haven't found output curves for ProMaster alternators, but have for the Ford E-Series which I expect have curves similar in shape. I'd also expect similar performance relative to rated capacity.

Available output of this 150 Amp Ford alternator is a function of RPMs and temperature. Please note alternator spins 3 times faster than engine. Curves for 240 Amp Ford alternator are a little flatter.
 

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https://www.nationsstarteralternato...er-Ram-3-6L-V6-Pentastar-XP-p/11572-270xp.htm
Even if this bolts up to the engine and fits in the promaster 3.6l you will need a smaller belt with 6 grooves and the other pulleys would also need to be 6 groove. These high output alternators have a smaller diameter pulley to spin faster at low engine rpm. They generate more heat than oem and need to be heavy duty. Oem are designed to operate what came with the vehicle and not much else.
Search for high output alternators these are made for service trucks and snow plow trucks. And read up on high output alternators. There are more alternators, from other manufacturers, than the one I listed.
 

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Hi,
If we are thinking about alternator output to charge house batteries, the alternator output to the house battery also depends on the type of battery and the state of charge of the battery.

I have two 220AH FLA golf cart batteries in series and have monitored the charge current on a few occasions. The most I've seen is 38 amps with the batteries at a pretty low state of charge, but this is only for a short time when the batteries are at a low state of charge. It quickly drops down about 20 amps or less.

I have a 50 amp breaker on line from alternator to house battery and this has never tripped. I was concerned about the charge rate exceeding what the golf cart batteries are designed for and set the breaker small enough to catch charging at too high a rate.

Gary
 

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....cut....

I have two 220AH FLA golf cart batteries in series and have monitored the charge current on a few occasions. The most I've seen is 38 amps with the batteries at a pretty low state of charge, but this is only for a short time when the batteries are at a low state of charge. It quickly drops down about 20 amps or less.

....cut....
Gary, is it fair to say that when you're at +/- 50% state of charge it then takes "about" 5 hours of driving to get them fully charged?

That's a long time, which is one reason AGMs may be a better choice for some applications. On the other hand it also confirms RDs point of view that a standard alternator may be all you need -- not much benefit to upsize to a higher capacity alternator if only pulling 20~38 Amps.

Obviously a larger battery bank, AGMs, or lithium batteries could change alternator requirements.
 

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Gary, is it fair to say that when you're at +/- 50% state of charge it then takes "about" 5 hours of driving to get them fully charged?

That's a long time, which is one reason AGMs may be a better choice for some applications. On the other hand it also confirms RDs point of view that a standard alternator may be all you need -- not much benefit to upsize to a higher capacity alternator if only pulling 20~38 Amps.

Obviously a larger battery bank, AGMs, or lithium batteries could change alternator requirements.
Hi,
I'd say it probably is true that it does take that amount of time under those conditions, but I very rarely get down to 50% state of charge and I have the 315 watts of solar to add to the charge rate. So, for my particular use, the fairly low charge rate from the alternator is not a problem.

Not sure how much different the charge rate would be if I had same size AGMs -- it would be really nice for someone with AGMs to take some charge rate measurements. Data are good :)

Gary
 

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Sorry, apparently I've become so used to alternative facts, I've forgotten what do with real data, Gary.;)
I do plan on monitoring the isolator circuit on our 500A AGM bank. You can't manage if you don't monitor.
 

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There are Chrysler alternator output graphs linked from the Ram Body Builders Guide for the RAM trucks, and the RAM 1500 LD has an alternator with the same order code BAJ for 220 Amp alternator.

I expect the pulley ratios are different, but the alternator output is likely pretty similar. Even if these are accurate, at 800 RPM engine idle, the alternator will output 140-165 A with a 3:1 ratio, so well below max output.



original image link (resized version above)
 

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An interesting chart and one we looked at when we purchased our Nations 280 amp second alternator. The difficulty is: It's theoretical and practically meaningless in the real world.

That an alternator is 'rated' for (i.e. permits) these high current levels doesn't mean that it will actually deliver such high current. The fact is, it wouldn't come close unless you have a programmable (generally external) regulator which allows running the alternator output voltage as high as required to meet the desired current objective. With such a regulator, one will discover that the output voltage of the alternator is constantly increasing in order to offset the corresponding increase in battery voltage as the battery charges.

In the real world of ProMaster alternators, whether high capacity or not, the regulator will be set to a target charge voltage (which may be a function of temperature and other factors) in the mid 14v range - - which voltage is not high enough to cause the alternator to 'put-out' those high theoretical current levels. And to the extent that your large, discharged house battery 'accepts' an impressively high number of amps when the alternator is first enabled - - your joy will quickly be replaced by disappointment when you discover that those high initial charge rates drop dramatically literally within just a couple of minutes.

If you want to take advantage of those high theoretical current levels, you'll have to outsmart your hamstrung alternator. And that's why those increasingly popular 'step-up' battery-to-battery chargers are gaining traction - - they can accept your fixed 14+ voltage alternator output and step it up to a controlled/programmable higher voltage required to charge your house battery at a sustained high level.
 

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Hi,
I think Winston hit the nail on the head. The alternator may be theoretically be able to produce those high currents but its not going to happen if you just hook it to your house battery.

It matches what happens when I measure charging current to my house battery -- fairly high for a short period of time when batteries are well down, but quickly drops to lower values.

I guess the question everyone has to ask for their situation is do I really need those high charge rates -- for me the answer is definitely not.

Gary
 

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And battery choice drives the way you look at charging systems. Team FLA wonders what the all the fuss is about. Team AGM is tempted by B2B solutions, but not sure they will do the job or are worth the expense. Team Lithium has already abandoned expense arguments, so why not get a second alternator while you’re at it and be done with it. And Team Undecided is thoroughly confused ;)
 

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I think voltage drop is the main reason the "expected" high currents aren't realized. That seems the simplest explanation.

As the alternator gets hot (or warmer) the voltage output will decrease. If van is stationary then under-hood temperatures could climb faster (particularly on a warm day trying to output high current). If you're trying to get 100 Amps from a high-capacity alternator to the back of the van where the (high capacity) house batteries may be located, what's the voltage drop? If you run 10 to 15 feet or more of cable, what size cable is it, and what's voltage drop getting to house batteries? If you start with 13 Volts at alternator and drop another 1/2 Volt in the cables, can 100 Amps flow into batteries at 12.5 Volts? Probably not, so system will equalize at some much lower current.

I'd want to see much data on voltage versus current at the house batteries before concluding much of anything. :)
 
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