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Old 09-21-2015, 08:20 PM   #1
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which charges better?

The answer may be in a thread, but I could not find it.

Which charges house batteries quicker, an hour of driving or an hour of generating while parked?

I know there are variables, but just looking for a general answer.

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Old 09-21-2015, 08:35 PM   #2
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Depends upon how powerful your converter/charger is. The device which converts 110 volts AC to 12 volts DC AND charges your batteries.

Generally I would say using the generator while parked is going to charge the batteries quicker. This is because engine alternators are really not designed to recharge "dead" batteries.....they are mostly just designed to replace the electricity being used as you drive.

Also modern converter/chargers are "multi-stage" chargers....meaning that they are "smart" and tailor the current and voltage in three (or 4) "stages" to recharge the batteries most efficiently. Alternators use a voltage regulator which is "fixed" at just one voltage.

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Old 09-21-2015, 08:38 PM   #3
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Variables are alternator amps vs converter/charger amps.

Maintaining engine rpm the keep the alternator charge rate at max. another.

Easiest most constant charge rate would be the gen set.

One hour of straight freeway driving would be the quickest.
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Old 09-21-2015, 08:48 PM   #4
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This is quoted from the progressive dynamics website.

One disadvantage of recharging a lead acid battery at a fixed voltage of 13.6-volts is the recharge time is very long. A typical 125-AH RV or Marine battery will take approximately 80 hours to recharge at 13.6 volts. Increasing the charge voltage to 14.4-volts will reduce battery recharge time for a 125-AH battery to 3-4 hours. Once a battery reaches 90% of full charge, the voltage must be reduced from 14.4-volts to 13.6-volts to reduce gassing and water loss. The optional Charge Wizard automatically senses when a battery has a very low state of charge and automatically selects its BOOST MODE of operation. BOOST MODE increases the voltage of a PD9100 Series converter/charger to 14.4 volts. When the battery reaches the 90% charge level, the Charge Wizard automatically reduces the charge voltage down to 13.6 volts to complete the charge. Again, this is a standard feature on our Marine Chargers.
Another disadvantage of recharging a lead acid battery at a fixed voltage of 13.6-volts is that once it is fully charged, 13.6 volts will cause considerable gassing and water loss. To prevent this from occurring the charging voltage must be reduced to 13.2-volts. The Charge Wizard will automatically select its STORAGE MODE of operation (13.2-volts) once the battery reaches full charge and remains unused for a period of 30 hours. This feature is standard on all of Progressive Dynamics Marine Battery Chargers.
At a charging voltage of 13.2 volts, the converter/charger will maintain a full charge, reduce gassing and water loss. However, this lower voltage does not provide enough gassing to prevent a battery condition called Battery Stratification. Battery Stratification is caused by the fact that the electrolyte in the battery is a mixture of water and acid and, like all mixtures, one component, the acid, is heavier than water. Therefore, acid will begin to settle and concentrate at the bottom of the battery (see figure #8).

If your converter is not very powerful, you can upgrade to one like this one (80 amps)

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Old 09-21-2015, 09:22 PM   #5
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The quote from progressive is comparing an old, constant 13.6 volt converter, to a 3 stage smart one.

Engine alternators are capable of charging up to 14 volts or more.

You would need to know what your alternator amp output is, to compare with your charger, to answer your question.

A 100 amp alternator will easily output at least 60 amps, going down the highway, if the batteries are "low", without overloading it.

The engine alternator is upgraded in MH chassis to charge low house batteries, thru the bi directional charging controls, while supplying chassis loads.

Proof of its ability to charge, is the common practice of using the boost switch to get a MH engine started, when the chassis batteries won't do it. Once It's started, the alternator charges away.

A few hours latter, your chassis and house batteries are charged.
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Old 09-21-2015, 09:55 PM   #6
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How does one find out the alternator amp output?
My converter/charger is an IOTA DLS and is a 55 amp output.
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Old 09-21-2015, 09:59 PM   #7
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Look up a replacement on NAPA, using your VIN # .

They may list the amps.
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Old 09-22-2015, 05:23 AM   #8
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There is more to it than alternator amps. Since the alternator is usually pretty far from the house batteries, it really matters what wire gauge size was used.....too small a wire, and voltage is lost through the resistance of the wire (pretty common in fact).

Also many installations use a solid state battery isolator which allows the alternator to charge both chassis and house batteries, BUT isolates them so that draining one, does NOT drain the other.....my point being that this device uses diodes, AND because of the forward voltage drop across diodes, the house batteries will see 0.6 volts less than the chassis batteries.....add in the voltage drop from the undersized wiring (another 5% or 0.7 volts) and now you have a maximum charge voltage at the house batteries of 12.9 volts ( barely a trickle charge ). You will only know by measuring your own system at the batteries with an accurate voltage meter.

The onboard IOTA charger will most likely charge much faster because it is closer to the house batteries, uses larger gauge wiring, and does not have to pass current through a battery isolator diode.
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Old 09-22-2015, 06:45 AM   #9
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In a properly wired solid state, diode isolator system, a voltage sense wire will run directly from the start battery to the alternator regulator. It will detect the actual battery voltage, causing the alternator to overcome the diode loss. There is still a slight loss to the house battery, but not quite as bad as stated, otherwise they wouldn't have used isolators in many older MHs.

As far as the wire gauge, if it was a proper installation, the wire would have been suficant to carry a charge.

Now days, diode based isolators have become obsolete and replaced by voltage sensing circuits, controlling solenoids, that cross connect the batteries with large battery cables.

Even my 1999 Class C uses battery cable, capable of carrying 200 amps, and a solenoid to cross connect my batteries that are 15 feet apart.

When paralleling the batteries, the charged one boosts the low one while the high charging current brings the low one up, until equal.

We camp at Wal-Mart and Flying J, often.
With using the lights, Sat. TV and electric coffee maker, my batteries are usually low in the morning.
I start my engine, drive to my next stop and have charged batteries.
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Old 09-23-2015, 07:24 AM   #10
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There's a good reason they stopped using the diode type isolators quite a while ago. Relay types far more efficient.

I think it safe to say most engine alternators (used on motorhomes) will put out in excess of 100a peak.
Consider also that when the engine is started, the isolator relay closes, which allows current from the main battery to start charging the house/aux batteries immediately, even if the alternator wasn't working (thus the need for large cables between them).

So, regarding the OP's question, my vote would be that the engine alternator would be the faster way to charge house batteries - by quite a bit.
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Old 09-23-2015, 07:41 AM   #11
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It depends on state of charge and the components of the charging system.

If you are with a low battery and can start the engine then do so and go.

If you just want to top off the batteries then start the genny and have lunch.

In general it does not matter that much but circumstances may set the direction.
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Old 09-25-2015, 08:48 AM   #12
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We have a 150A output off of the engine, and it brings our coach batteries to full SOC while driving very well.

Our MS2812 Inverter/Charger, also will bring out house batteries up to 90% SOC within 2 - 2 1/2 hours, when starting from SOC of between 70-75%. I've seen start up bulk charge values of GT 100A from the BMK-Meter readings. (This is the same with either generator or shore power feeds).

As Tony (TQ60) stated 'it depends' on many factors. One variable probably inferred in Tony's post under 'components of the charging systems.' Is the bank size, and battery type. AGM's can take a higher charge, and recover faster, the lead. Lifeline AGM's can take a higher charge, and recover slightly faster then other AGM's.

And again, commenting on Tony's comments, I agree is generally does not matter. If driving anyways, and you have one of the newer non diode related systems - it should cover what you need on charging. If not, you can always fire up the generator if you want more once you are at location.

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Old 09-25-2015, 04:42 PM   #13
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Originally Posted by rrodda1 View Post
How does one find out the alternator amp output?
My converter/charger is an IOTA DLS and is a 55 amp output.
It is stamped somewhere on the alternator housing but that's not the end of the math.. you need to know not how much the thing can put out but rather how much is LEFT OVER. Here is the easy way to do that...

First you need a DC Clamp on ammeter.. OR: a battery moni9tor system such as the Tri-Metric.

(I would use my Sears Clamp on AC/DC ammeter)

Now run batteries down to half full (Deep cycle) or around 70 percent (MARINE DEEP CYCLE.. and clamp on. Fire up that big engine and accelerate to an RPM that you would expect to see at say 60MPH,, Say 20,000 RPM. READ meter.

Shut down.. Plug in.. READ METER

You now have your answer.

Oh you clamp on any SINGLE battery lead.. If you have ONE Pair GC2 the jumper will do, IF you have multipe pair and/or multiple 12 volt in parallel usually there is one and only one NEGATIVE wire.. On my RV there are two Positive wires but they are in parallel (Both go from the same Terminal A to the same Terminal B so you violate the meter instructions and clamp around the pair of 'em)
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Old 09-25-2015, 04:52 PM   #14
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I know on my 2012 Ford F 250.. there is a 25 amp fuse between the truck and the travel trailer battery..... so truck alternator may not exceed 25 amps to the trailer battery or the fuse will blow....

my travel trailer has a 55 amp smart charger..... so it would be faster

and my Truck as a 155 amp alternator.

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