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Old 04-20-2017, 11:56 AM   #1
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What charges batteries faster? Gen or Engine?

I would think the batteries would charge faster with the cab engine. The alternator is putting out 12V directly, whereas the generator has to convert from 120V to 12V. That has to be less efficient, but is it that much slower?

Since I mainly boondock, this is more a matter of saving propane (cab has a diesel engine), but if one way is significantly faster I'm all ears...
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Old 04-20-2017, 02:01 PM   #2
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Maybe even a decent battery charger plugged into your generator you'd probably get 12-15A. 12 v side of gen not usually high out put amperage from my expereience. Alternator out put from vehicles not really high flow at idle, you'd have to keep it revved up which would be a PIA an not real economical. Check out the numbers
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Old 04-20-2017, 05:46 PM   #3
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Soooo, neither is fast, eh? A battery charger plugged into 110 would be faster, more effective? Seems to be more or less what the motorhome's WECO inverter is doing already, no?

I carry a charger anyway with me while camping to charge a stand-alone spare battery with an inverter (mainly to charge phones, Ipads, laptops). I've got a clamp on amp meter that works for 12 V - I could check it out.
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Old 04-21-2017, 06:22 AM   #4
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It would depend on what kind of converter you have.

If you have one of the three (or four) stage converters, one of the "stages" is a BOOST , or fast charge mode, This mode can put out full amperage to charge the battery.

As for the engine charging, If its running at high RPM (not idling) I would say in most cases, this will charge the battery faster.
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Old 04-21-2017, 12:15 PM   #5
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Old 04-21-2017, 01:15 PM   #6
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I also have wondered this. It seems modern engines have at least a 100 amp alternator that would have a high output at lower rpms and charge quicker than the 20-30 amp WFCO converter I have. It also charges at high output at 14.2 volts initially versus the 13.6 from the converter.
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Old 04-21-2017, 01:40 PM   #7
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battery charger and converter interference?

If one used a 110 volt battery charger would that trick the converter into thinking there was more charge than was actually there. Thus the converter would shut or slow down?

In other words what happens when two chargers are run concurrently? In a past motorhome I had one bank of two batteries and three in another bank. I separated them and used the 110 volt charger on the three bank and left the two bank on the converter when charging in a hurry.

I did not know if that was a good idea or not. But did it anyway thinking the interference theory might be real.

Does anybody know if using a regular car charger in conjunction with the converter is too much juice or perhaps confusing the two chargers?
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Old 04-21-2017, 01:59 PM   #8
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The answer is that it all depends..... if BOTH the engine alternator AND the converter are capable of putting our amperage in excess of 25% of the battery bank amp hour capacity...then BOTH will take an equal time to charge since a battery cannot accept more than 20-25% of it's capacity in the bulk charge mode. In other words if you have a 100 amp hour battery than NOTHING that puts out more than 25 amps will affect the time it takes to charge.
This applies to wet cells. AGM's can be charged at higher rates.

Now if you DO have a charger that can put out 25% of your battery capacity...and you use only 50% of your battery capacity before recharging (as you should if you don't want to damage your battery life!) ...then in that same 100amp hour battery...you are trying to put back 50amp hours AT 25 amps of current. Make sense??
Unfortunately...that doesn't mean 2 hours. Batteries RESIST charging current as they begin to get full. You can be sure that if TWO hours is what it would take on a linear basis...it will be 4 hours or more on an actual basis.
Thus...the only way to speed up charging time from any charging system that can provide at least 25% of your battery banks rating...is to buy AGM or LiFePO4 batteries.
Otherwise it will take at least 4 hours and you kill your batteries a little every time you don't do it all the way because you are leaving lead sulphate on the plates to crystallize and harden.
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Old 04-21-2017, 02:03 PM   #9
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Quote:
Originally Posted by daveinthekeys View Post
If one used a 110 volt battery charger would that trick the converter into thinking there was more charge than was actually there. Thus the converter would shut or slow down?

In other words what happens when two chargers are run concurrently? In a past motorhome I had one bank of two batteries and three in another bank. I separated them and used the 110 volt charger on the three bank and left the two bank on the converter when charging in a hurry.

I did not know if that was a good idea or not. But did it anyway thinking the interference theory might be real.

Does anybody know if using a regular car charger in conjunction with the converter is too much juice or perhaps confusing the two chargers?
To my limited knowledge, if you put a battery charger on you house batteries, it would defeat your converter because it would sense a high voltage and think your batteries are charged and not provide additional charge.
The same would happen if you had 2 banks of batteries unless you had them totally disconnected from each other. The quickest way would be to disconnect the two banks of batteries and let the converter charge one and a separate car charger charge the other. This way they can charge the battery banks independently.
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Old 04-21-2017, 02:05 PM   #10
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ahh... but it is even a little more complicated than that if you have a residential refrigerator, which I do. My engine alternator puts out nearly 14.1 volts and more current than my PD converter with the generator running, at least 8 or 9 maps more. So, one would think that the engine would be best. HOWEVER, if the reefer runs a power cycle during the 3 hours or so, which is inevitable, it will pull at least 15 amps out of the bank while running. If I run the generator the reefer is powered by AC from the generator so that method gets an additional 8 or 10 amps average, even though the converter puts out less amperage into the batteries. In my case, the generator/converter is a better route.
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