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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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Old 04-21-2017, 02:44 PM   #11
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Amps is amps

Gentleman: Amps is amps, no matter where it is from. All the so called rules fit in a category I call Dock Talk. Charging a battery is like eating. Depending on size, age, hunger, size of plate, .... It is not a physical reaction like most think. It is more chemical and strange at that. Otherwise, it would just be amps/rate = time. The bulk rate is when the battery is mostly discharged, then acceptance and then float. Any decent charger actually will go in and out of all 3 phase until the battery reaches 100%. That takes from 12-48 hours. If a 100 amp battery is fully discharged IT Will accept more than 25 amps. Again, all these so called rules are not rules, just hearsay. A standard wet cell will not charge as fast as an AGM, but if the battery bank is large, that is a moot point, both banks will charge at the same rate. I'd post a link, that details this much more, but ...
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Old 04-21-2017, 03:09 PM   #12
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I on't know if my charger has 4 modes, but I'm pretty sure it has 3. I can't force it into a certain boost mode, but I think it goes into the high charge mode first.

Solar - I use several small portable solar collector panels to keep small lithium batteries charged up. However, the batteries I've bought in the last year are big enough that all my phones and tablets can stay charged over a long weekend of boondocking. Maybe someday I'll get ambitious enough to install a decent sized roof panel, but with all LED interior lighting the current draw isn't too bad. I checked out the lithium RV batteries from BattleBorn and SmartBattery, but I'm not ready to fork over $900-1,000 per battery.

I go yearly to a 3 day music festival at Grand Targhee, Wyoming that works out to more like 5 days of camping without shore power. I don't want to disturb the RV parking lot any more than I need to, hence the question.
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Old 04-21-2017, 05:01 PM   #13
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battery charging faster....

I read through this post and I didn't see the answer that explained well how this works electrically, so I am jumping in.

The question was which charges the battery faster.. Generator or engine?
The question does not provide enough information to be able to answer as the determining factor for how fast a battery can be charged is simply the max current rated output of the charger. So unless you have a huge generator.. Your +90 amp alternator in your vehicle will always be capable of charging faster as most generator or AC plugged in chargers are 10 to 20 amps. Yes there are huge chargers that have higher charging amps, but nobody would normally have something that big.

BUT let me try to explain the theory on how this works electrically. The amount of current supplied while charging a battery is dependent on the battery voltage level. A dead battery at <6 VDC is going to put a huge current load on a charger that wants to raise the voltage to the typical charging voltage of 14.1 to 14.3 VDC. It would take 100's of amps if the charger could supply it. But the current supply from the charger is limited by it's current capacity. A 10 amp charger will only be able to supply a max of 10 amps and so the voltage on the battery will initially go from <6 VDC to maybe 7 to 8 VDC and slowly rise to the full charge voltage of 14 VDC. The larger the battery capacity rating, the longer this will take. Now take that same situation and put a 50 amp charger on it. The initial battery voltage will be 10 to 12VDC and it will rise to the 14 VDC level much sooner.
BUT!!! Faster charging is not necessarily better as you can "boil" your battery if you charge too fast. To state this in the extreme... If you had a good battery that is dead and you hooked it up to a fully charged battery with heavy duty jumper cables, you could easily explode your battery and melt your jumper cables as there is no current limit between the dead and fully charged battery... NEVER DO THIS!!!

The other variable on how fast chargers can charge is the voltage level the charger regulator tries to charge the battery to. This should never be above 14.4 VDC and if it goes higher it will "boil" your battery. The smart chargers will change the voltage level it is charging to a lower level to keep from overcharging the battery.

I always use water as a way to explain how this works electrically. Voltage is like water pressure (PSI vs voltage) and current is water flow (GPM vs amps). If the battery was a 100 gallon tank with 50 gallons in it and you wanted to charge it from 1/2 to full capacity (fill it to 100 gallons). Then the variables that effect how fast that happens are the hose pressure (PSI vs voltage) and the hose size (GPM vs amps). The higher the pressure and the bigger the hose, the faster you are going to fill the 100 gallon tank. And yes, there are interdependencies between the pressure and GPM as there is more flow at higher pressures (higher voltage) and higher flow with larger hose size. And just like the battery... if you have the pressure and flow too high for the tank, then you could blow the tank or the hose up.

Adding a 10 amp AC charger on top of an internal 10 amp converter charger will reduce the charging time as they will provide more total charging current, but they both will only try to charge to ~14 VDC. Think of it as two hoses filling the 100 gallon tank instead of one. So current from each will raise the voltage helping each other, but they will "share" the charging and each will reduce it charging level as the battery voltage increases. You do not need to worry about them "fighting" each other... Instead, they will compliment each other, but they will never exceed the max charging voltage level so they will lower their charging current as the battery voltage increases. (they won't overfill the 100 gallon tank)

Thanks
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Old 04-21-2017, 06:53 PM   #14
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It is well known that WFCO converter/chargers spend most of their time outputting only 13.6 volts, even though they claim to have a "Bulk" mode in the 14 volt range. As a result, it takes a lot longer than it should to charge the batteries.

I use a dedicated 15 amp battery charger from my genny when I boondock and need to recharge. It outputs 14.4 volts for most of the charge cycle, and has an "Engine start" mode that puts out 15.5 volts that I can use to equalize my battery.
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Old 04-21-2017, 10:56 PM   #15
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Before we were on the solar bandwagon, I kept a battery charger in place and when batteries were low the generator ran the converter and the 50 amp mode on the little harbor freight charger WAS MY BOOST CHARGE. Jumper the batteries back to 80 % or so Really Fast.
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Old 04-26-2017, 03:46 PM   #16
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I've got an old 12V charger that has a 100 volt jumper setting. However, it's not very little. I think the thing weighs about 20 lbs, about the size of a cinder block. I've seen similar ones that even have wheels.

I took a look at the Harbor Freight model (10/2/50 amp 12V). Both versions are about 11 lbs. Not that much different than the unit I already have. Does it bog down the generator while it's running 50 amps?
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Old 04-26-2017, 03:51 PM   #17
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I've got an old 12V charger that has a 100 volt jumper setting. However, it's not very little. I think the thing weighs about 20 lbs, about the size of a cinder block. I've seen similar ones that even have wheels.

I took a look at the Harbor Freight model (10/2/50 amp 12V). Both versions are about 11 lbs. Not that much different than the unit I already have. Does it bog down the generator while it's running 50 amps?
50amps of DC charging current wont bog down anything as it is only 600 watts of power... the equivalent of around 5 AC amps from your generator.
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Old 04-26-2017, 04:00 PM   #18
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Engine alternators make terrible chargers for deep cycle batteries. They work great at supplying the juice required to run the accessories powered by the engine and replacing the juice needed to start it. A discharged deep cycle battery needs lots of juice and a long time to refill all that storage.

See the attached article for a full discussion.

I just hook up a dedicated multistage battery charger to the generator and let it run for several hours. Full top up requires shore power and a day or so due to the required low flow rate above 90%.
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File Type: pdf Automobile Alternators as Chargers.pdf (805.9 KB, 46 views)
File Type: pdf Trojan battery user guide.pdf (548.6 KB, 30 views)
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Old 04-28-2017, 03:49 PM   #19
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I've got an old 12V charger that has a 100 volt jumper setting. However, it's not very little. I think the thing weighs about 20 lbs, about the size of a cinder block. I've seen similar ones that even have wheels.

I took a look at the Harbor Freight model (10/2/50 amp 12V). Both versions are about 11 lbs. Not that much different than the unit I already have. Does it bog down the generator while it's running 50 amps?
This is all you need. https://www.amazon.com/Schumacher-SS...attery+charger

Hook it up to the generator and let it run a few hours. If you don't let your battery discharge below 50% capacity (12.0 volts or so), that should recover you to at least 90%.

50% remaining is when the "Good" light (third light) goes out on the panel (2 lights remain on). You should recharge immediately (or as soon as possible) at this point. Waiting till the "FAIR" light goes out (1 light lit) will ensure permanent battery capacity loss.

Remember 4 lights "on" in the panel is (C) "charging" and will go out as soon as the surface charge is depleted after the charger is removed. It does not mean "Full"; that is only for the holding tanks.
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Old 04-28-2017, 05:34 PM   #20
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The Schumacher looks like a nice unit. I'll bet adding something like this to charge every time I run the genny will help.

Usually I'm at around 11.8 amps after 2.5 days of boondocking; that's with running the genny maybe 15 minutes a day to make coffee and run the microwave. I would guess the biggest draw is running the furnace at night (8500' elevation gets cold, even in the summer).
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