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How do I calculate the inverter / batteries / Solar panel thingy?


MoonTimber

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OK, so did I do it right?

 

Looks good. You could actually draw down as low as 50%, but the higher soc you can maintain on a regular basis will help improve the longevity of your battery bank.

 

In your calculations you also need to consider the base line draw of your rig as well. That will be the sum of your 12v appliances in 'idle' + parasitic draw. It generally doesn't amount to much.. maybe an amp or so, but that will be a 24 hour draw. So with a smaller bank where your available ah's (50%) is only 100ah, you might have to skim 24ah's right of the top before you work in your typical daily consumption.

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Moon Timber, YOU ARE A good student!!!!!!!! I think we have all drilled the concept of Battery Stored Energy in the form of available Amp Hours and Instantaneous Power in Watts (Volts x Amps) and Energy use (Volts x Amps x Time IE Watt Hours) Its similar to how the electric utility charges you for the Killowatt Hours of Energy you use which is again Volts x Amps x Time. Battery stored energy is represented in Amp Hours (Amps x Time) while 120 VAC (or Inverter) is often represented as Watt Hours (Watts x Time). You know the old saying "Catch a man a fish you feed him a day, teach a man how to fish you feed him a lifetime" Therefore here's my feeble attempt to teach you the theory so you understand it and how and why those formulas operate

 

"OK, so did I do it right?"

 

"1 Laptop at 45W + 1 laptop at 25W + 1 Television at 60W = 130W."

 

YES the total running watts (if that's your actual use??, Im NOT assuming other loads or guessing others, I take you at your word and indeed figure 130 watts)

 

"Your formula: 130W / 12 (Volts) = 10.83 Amps"

 

FYI what you're doing here is to convert how may amps your battery must supply to the Inverter which Inverts 12 VDC to 120 VAC. Stored battery ENERGY is represented as AMP HOURS while normal 120 VAC Utility ENERGY (and what your 120 VAC output Inverter supplies) is represented as Watt (Or Kilowatt) Hours. TO CONVERT WATT HOURS INTO AMP HOURS

 

Watts = Volts x Amps, Therefore 130 Watts = 12 Volts x ? Amps,,,,,,,,,Therefore Amps (at 12 VDC) = 130/12 = 10.83 Amps THIS MEANS YOU BATTERIES MUST DELIVER 10.83 AMPS TO POWER YOUR 130 WATT 120 VAC LOADS (2 laptops + TV).

 

"My two batteries provide 202Amps. Amps are Amps per Hour or Ah (Right?)."

202Ah / 10.83 = 18.65 hrs.

 

YES, I would say your batteries STORE 202 Amp Hours of Energy. Think of that as it can supply 1 amp for 202 Hours or say 10 amps for 20.2 Hours. THEREFORE if you are drawing 10.83 Amps your 202 Amp Hour rated batteries could supply those amps for 202/10.83= 18.65 Hours. BUT AS YOU NOTED THAT DOES NOT ALLOW FOR 10% LOSS AND 90% OF 18.65 = 16.78 hOURS

 

NOW even though those are the theoretical battery ratings, to increase battery longevity, I prefer to only deplete their energy to one half or less of their rating

 

THEREFORE I would conservatively choose to operate those 130 watt loads for 1/2 of 16.78 or around 8 Hours

 

SUMMARY we have gave you the formulas,

Watts = Volts x Amps

Energy is Instantaneous Power in Watts X Time

Stored Battery Energy is represented in Amp Hours, i.e how may amps it can supply for how much time. Think of it as a 202 Amp Hour Battery can supply 1 amp for 202 Hours. NOTE Im NOT going into the 1 versus 20 amp calculations so don't anyone have a calf lol

To convert Watts into Amps, Divide Watts by Volts, IE 120 Watts at 12 Battery Volts = 120/12 = 10 Amps

 

I have tried to explain them and the theory, now its your choice. If you have any more questions post back and myself and the other fine gents here will try to help.

 

John T

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Good teaching, guys.

 

The only thing I did not see here that should be accounted for is the ACTUAL stored energy in the battery bank. It will NOT be the rated amount. It is ALWAYS less. SO if you work off the ratings and use 50% you are going to be stressing the bank, for sure, in my opinion. And if there are any used batteries in the picture it will be significantly less. This is why I design for a 30% drawdown and then make tradeoffs from there.

Jack & Danielle Mayer #60376 Lifetime Member
Living on the road since 2000

PLEASE no PM's. Email me. jackdanmayer AT gmail
2016 DRV Houston 44' 5er (we still have it)
2022 New Horizons 43' 5er
2016 Itasca 27N 28' motorhome 
2019 Volvo 860, D13 455/1850, 236" wb, I-Shift, battery-based APU
No truck at the moment - we use one of our demo units
2016 smart Passion, piggyback on the truck
-------------------------------------------------------------------------
See our website for info on New Horizons 5th wheels, HDTs as tow vehicles, communications on the road, and use of solar power
www.jackdanmayer.com
Principal in RVH Lifestyles. RVH-Lifestyles.com

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Good teaching, guys.

 

The only thing I did not see here that should be accounted for is the ACTUAL stored energy in the battery bank. It will NOT be the rated amount. It is ALWAYS less. SO if you work off the ratings and use 50% you are going to be stressing the bank, for sure, in my opinion. And if there are any used batteries in the picture it will be significantly less. This is why I design for a 30% drawdown and then make tradeoffs from there.

This is why I usually check the TriMetric first thing every morning. This is usually the low point in the cycle and the condition of the battery bank determines whether I decide to wait for the sun to get high enough to start putting some juice back into the "tanks" or start the generator. (Well, that and how bad I want a big breakfast.)

 

I don't know if everyone is like this but I usually have an inkling of what the battery bank's state of charge will be even before I get up.

 

WDR

1993 Foretravel U225 with Pacbrake and 5.9 Cummins with Banks

1999 Jeep Wrangler, 4" lift and 33" tires

Raspberry Pi Coach Computer

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Desert rat,

 

I use the same method. But I often hit the genset for 15-30 minutes even if I think I will top up with solar. That way I can make coffee, do toast, whatever and not add to the deficit. Plus exercise the genny.

Jack & Danielle Mayer #60376 Lifetime Member
Living on the road since 2000

PLEASE no PM's. Email me. jackdanmayer AT gmail
2016 DRV Houston 44' 5er (we still have it)
2022 New Horizons 43' 5er
2016 Itasca 27N 28' motorhome 
2019 Volvo 860, D13 455/1850, 236" wb, I-Shift, battery-based APU
No truck at the moment - we use one of our demo units
2016 smart Passion, piggyback on the truck
-------------------------------------------------------------------------
See our website for info on New Horizons 5th wheels, HDTs as tow vehicles, communications on the road, and use of solar power
www.jackdanmayer.com
Principal in RVH Lifestyles. RVH-Lifestyles.com

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Desert rat,

 

I use the same method. But I often hit the genset for 15-30 minutes even if I think I will top up with solar. That way I can make coffee, do toast, whatever and not add to the deficit. Plus exercise the genny.

It's easier if you don't have to get out of bed to start it. :P

 

WDR

1993 Foretravel U225 with Pacbrake and 5.9 Cummins with Banks

1999 Jeep Wrangler, 4" lift and 33" tires

Raspberry Pi Coach Computer

Ham Radio

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I think you have all your numbers right too, if you factor in the expected losses. I'd also worry about battery lifetime with a 50% discharge and as was mentioned as the batteries age that will edge higher. I'd really want to stay with using just 30% of new batteries capacity which is going to edge up as they age and drop storage ability.

 

Get the life cycle / discharge level chart for your batteries and see if it is going to be cheaper to stress and replace your batteries or if it will save money to add more batteries to cut the stress by half and extend the lifetime of the batteries. If you can't or decide not to expand then just plan on the early replacement and don't worry about it.

First rule of computer consulting:

Sell a customer a Linux computer and you'll eat for a day.

Sell a customer a Windows computer and you'll eat for a lifetime.

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Jack says

 

"The only thing I did not see here that should be accounted for is the ACTUAL stored energy in the battery bank. It will NOT be the rated amount. It is ALWAYS less."

 

I AGREE 100% YOU ARE RIGHT ON IN MY ENGINEERS OPINION

 

Despite the theoretical ratings and supposed stored energy and all our calculations and formulas above, its been my personal practical experience you cant extract that much energy as the rated Amp Hours would suggest!!!!!!!!!! (Sure you can extract more energy, but at the cost of the battery falling to an extreme low state of charge!!!!) I don't like to go beyond 50% of the theoretical ratings and usually use even LESS before I fire up the genset if necessary or hopefully its morning and the solar kicks in. Even if I had enough battery capacity in the AM I usually fire up the genny to make coffee or perhaps the wife uses it for the hair dryer etc. and I usually let it run a while just for good measure for a good jump or kick start prior to the days solar charge up.

 

While most of us may understand it, the original poster may not realize a battery has only a finite x amount of LIFE CYCLES and the more often its deeply discharged and having to be replenished the more Life Cycles that are being consumed. Wise and prudent charging methods and monitoring such that a battery is hardly ever depleted or to only minimal amounts certainly extends battery life as its precious limited LIFE CYCLES aren't being fretted away lol Quality true deep cycle batteries with adequate amp hours of storage, sufficient and "Smart" 3 or 4 stage charging and Solar and wise genny use and monitoring is what its all about..........

.

GREAT CHAT YALL

 

John T

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We've been battling the flu, but I finally stopped in at Sams. Sure enough, they had the 6V golf cart batteries for $85, labeled as 75Ah. They also had Energizer Marine/RV batteries for $95 that are the same size group (29DC) as the one already in my RV. It's $5 less than walmart, but the walmart one says 101Ah where this one says 122Ah. Should I be able to buy this one and use it with my existing Walmart battery?

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The sam's club battery is either mislabeled or different from the golf cart sold at most Sam's or Costco's I have seen. I would try another Sam's. There are long threads in other forums discussing the variances in the golf cart batteries from these retailers. There are stories of mislabeled batteries and that some stores do offer different types of golf cart batteries than others although I have never heard of one rated as low as 75 ah. They typically rated 200 to 220 Ah. I see this on sam's

Sams Club: Emergizer battery, size CG2, 107 RC minutes @ 75 amps, 220AH, $81.83 ea....Are you sure you were looking at the AH?

 

 

With regard to the Walmart batteries, remember that matching does not focus only on physical size but on the age and rating of the batteries.

Dave and Lana Hasper

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To answer your question, yes you can add a new battery to an old battery. However the new batteries life will be reduced to about that of the old battery. In other words if you have one year left on your old battery and the new battery would normally last you 3 years, then adding the 2 together will double the ah capacity but they will only last as long as the oldest battery, in this case, 1 year. You will have lost 2 years use of that new battery making it cost you three times as much - hardly an economical choice. If your old battery is less than 6 months old you I would add another equivalent 12v in parallel. If older, I'd trade in your old battery and add 2, 6v GC-2s in series. If you have an older battery it may make economic sense to wait until the old battery completely dies and buy 2 new ones at the same time, regardless what type of battery you choose.

 

Chip

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Moon Guy, you ask:

 

"Sure enough, they had the 6V golf cart batteries for $85, labeled as 75Ah."

 

ANSWER

 

A few years back I bought I believe EG2 6 volt golf cart batteries at Sams for less then $100 that are rated at 230 AH, that 75 AH sounds awfully lowwwwwwwwwwww

 

 

"They also had Energizer Marine/RV batteries for $95 that are the same size group (29DC) as the one already in my RV."

 

ANSWER

 

OKAY those are semi deep cycle batteries and NOT the same as true deep cycle golf cart batteries. HOWEVER sure they will "work".

 

" It's $5 less than walmart, but the walmart one says 101Ah where this one says 122Ah. Should I be able to buy this one and use it with my existing Walmart battery? "

 

 

ANSWER

 

YES it will "work" HOWEVER ITS NOT THE PREFERRED ENGINEERING METHOD

 

Its best engineering wise if two batteries are the same size and type and design and age so the weak doesn't cannibalize the strong and they maintain equal charge states

 

 

BOTTOM LINE Sure adding another battery will "work" and provide additional energy storage amp hour capacity even if they are NOT a perfect match. You have heard us engineer and techy types describe whats best or preferred but its your money and now your call despite what we have to say.

 

You can spend $200 for two new 6 volt true dep cycle golf cart batteries,,,,,,,,,,,,,Or buy two new matched semi deep cycle RV/Marine 12 volt batteries for $200 (BUT NOT what Id do) ,,,,,,,,,,,Or buy one new 12 volt semi deep cycle RV/Marine battery for $100 and stick it in parallel with your old existing battery and it will "work" but not my preference for sure.

 

Hope this helps, I dont know what else we can tell you. YES IT WORKS NO ITS NOT BEST

 

John T

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Do not mix old and new batteries. Not unless the old one is really only a teenager.....if it is more than 6 months old (approximately) don't do it. It is false economy. You will not really save any money - you will shorten the life of the bank.

Jack & Danielle Mayer #60376 Lifetime Member
Living on the road since 2000

PLEASE no PM's. Email me. jackdanmayer AT gmail
2016 DRV Houston 44' 5er (we still have it)
2022 New Horizons 43' 5er
2016 Itasca 27N 28' motorhome 
2019 Volvo 860, D13 455/1850, 236" wb, I-Shift, battery-based APU
No truck at the moment - we use one of our demo units
2016 smart Passion, piggyback on the truck
-------------------------------------------------------------------------
See our website for info on New Horizons 5th wheels, HDTs as tow vehicles, communications on the road, and use of solar power
www.jackdanmayer.com
Principal in RVH Lifestyles. RVH-Lifestyles.com

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Yes, to clear this up, the "old" battery has a manufacturer date that's less than 4 months ago, and the previous owner said he just put it in about two months ago. It has barely been used.

 

My question had to do with the two batteries having different Ah ratings - Walmart at 101Ah, Sam's at 122Ah. Should I spend $5 more to get an exact match at Walmart, or will I be fine with the less expensive but apparently higher rated Sam's club battery?

 

Based on everyone's responses the golf cart battery is probably mislabeled. I went to the Sam's website and couldn't find any rating information. I went to the Energizer website and found even less! I'm still planning to get another marine/RV battery to match the one the previous owner installed but I haven't figured out how to "patch" it in yet. If it turns out to be a complex maze of spaghetti wiring I might go with golf cart batteries and set up a separate system so I can leave the stock system unchanged.

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Do you have room for 2 batteries next to each other? If you do I wouldn't start over on the wiring. You wire the batteries together, you don't splice the other battery seperately into the system. For your existing battery you would just wire the two batteries together in series.as follows : BATTER~4.gif

Dave and Lana Hasper

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Moon Timber's Latest Question:

 

"My question had to do with the two batteries having different Ah ratings - Walmart at 101Ah, Sam's at 122Ah. Should I spend $5 more to get an exact match at Walmart, or will I be fine with the less expensive but apparently higher rated Sam's club battery?"

 

MY ANSWER

 

If I recall, you're talking about placing the two 12 volt batteries in Parallel right?

If so my answer is: "EITHER" BATTERY WILL WORK IF ADDED IN PARALLEL TO YOUR EXISTING 12 VOLT BATTERY

If I were making the choice or the two mentioned, my old engineers brain would pick the one that's an exact match if only for $5 more HOWEVER again either will "work".

 

HERES THE DEAL

 

If you place two same voltage batteries in parallel, the Amp Hours (an approximation of available stored energy) IS ADDITIVE IE: A 101 AH in Parallel with another 101 AH EQUALS 202 AH

If you place two same voltage batteries in parallel, the available Cranking Amps IS ADDITIVE IE: If one had say 500 CCA two in parallel equals 1000 CCA

If you place two same voltage batteries in parallel, VOLTAGE DOES NOT ADD IE: If you had two 12 volt batteries wired in parallel, you still have 12 volts

If you place two same voltage batteries in parallel, a charger connected could deliver/divide the available amperage but both will get charged subject to battery condition and charger.

 

ITS BEST WHEN CONNECTING TWO BATTERIES IF THEIR SIZE AND DESIGN AND CONSTRUCTION AND AGE ARE IDENTICAL

BUT THAT DOES NOTTTTTTTTTTTTT MEAN THEY STILL WONT "WORK"

A CHAIN IS NO STRONGER THEN ITS WEAKEST LINK and its possible a weaker battery may draw off a stronger which is why its best if matched

 

Again, we tell you whats "best" and what will still "work" so its your money and your choice, but for ONLY 5 extra bucks, Id choose the battery that's the same rating.

 

More questions???

 

Best wishes yall

 

John T

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Do you have room for 2 batteries next to each other? If you do I wouldn't start over on the wiring. You wire the batteries together, you don't splice the other battery seperately into the system. For your existing battery you would just wire the two batteries together in series.as follows : BATTER~4.gif

 

Unfortunately, they decided to put the coach battery in the engine compartment. The Chassis battery is on the passenger side, the coach battery is on the driver side. It's a Ford Econoline, There is'nt enough space in there for an AA flashlight battery, never mind another automotive battery. Anything I add will have to be elsewhere in the RV. I'm hoping there is an easy path from the coach battery to one of the side compartments like where the water hose is stored. Then I would have to run a pair of long wires to wherever my new battery will end up.

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Moon Timber's Latest Question:

 

"My question had to do with the two batteries having different Ah ratings - Walmart at 101Ah, Sam's at 122Ah. Should I spend $5 more to get an exact match at Walmart, or will I be fine with the less expensive but apparently higher rated Sam's club battery?"

 

MY ANSWER

 

If I recall, you're talking about placing the two 12 volt batteries in Parallel right?

If so my answer is: "EITHER" BATTERY WILL WORK IF ADDED IN PARALLEL TO YOUR EXISTING 12 VOLT BATTERY

If I were making the choice or the two mentioned, my old engineers brain would pick the one that's an exact match if only for $5 more HOWEVER again either will "work".

 

HERES THE DEAL

 

If you place two same voltage batteries in parallel, the Amp Hours (an approximation of available stored energy) IS ADDITIVE IE: A 101 AH in Parallel with another 101 AH EQUALS 202 AH

If you place two same voltage batteries in parallel, the available Cranking Amps IS ADDITIVE IE: If one had say 500 CCA two in parallel equals 1000 CCA

If you place two same voltage batteries in parallel, VOLTAGE DOES NOT ADD IE: If you had two 12 volt batteries wired in parallel, you still have 12 volts

If you place two same voltage batteries in parallel, a charger connected could deliver/divide the available amperage but both will get charged subject to battery condition and charger.

 

ITS BEST WHEN CONNECTING TWO BATTERIES IF THEIR SIZE AND DESIGN AND CONSTRUCTION AND AGE ARE IDENTICAL

BUT THAT DOES NOTTTTTTTTTTTTT MEAN THEY STILL WONT "WORK"

A CHAIN IS NO STRONGER THEN ITS WEAKEST LINK and its possible a weaker battery may draw off a stronger which is why its best if matched

 

Again, we tell you whats "best" and what will still "work" so its your money and your choice, but for ONLY 5 extra bucks, Id choose the battery that's the same rating.

 

More questions???

 

Best wishes yall

 

John T

 

I'm planning to go parallel. Serial would really confuse me if it turns out I need to add a third battery three months from now. Sounds like I should get the second battery from Walmart!

 

I'm actually not sure how I would install a pair of golf cart batteries. If I were to remove the existing 12V coach battery a golf cart battery would not fit in the tight engine compartment battery tray. It would be too tall and wide. I suppose I would have to remove the existing "brand new" battery and leave the spot in the engine compartment empty, then connect cables to the battery cables and run them somewhere else?

 

My RV spent the night with my mechanic. Hopefully his wife isn't jealous. He is telling me my alternator is only putting out 12.6V and needs to be replaced. If we decide to replace it this would be a good opportunity to run wires.

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"A 100Amp Alternator, puts out 12V * 100 = 1200 Watts, right?"

 

You're on track. It may actually charge a battery at 14.2 volts and P = V x I,so Power in watts would = 1400. It may not pump a full 100 amps for an extended period, depends on batteries and loads, but hey that's its rating

 

"So is a 100 amp alternator equal to roughly ten 100 Watt Solar panels?"

 

IFFFFF the alternator was at ten volts and 100 amps, that's 1000 watts and ten 100 watt solar panels = 1000 watts. BOTH charge a 12 volt battery so charging voltage has to be greater then 12.6 you know..........

 

Power = V x I so BOTH enter the equation, but you have the idea down...

 

Of course, it takes a decent size motor to run that alternator while the solar panels just sit there in the sun!!!! If I recall 1 HP = 746 watts

 

John T

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"A 100Amp Alternator, puts out 12V * 100 = 1200 Watts, right?"

 

You're on track. It may actually charge a battery at 14.2 volts and P = V x I,so Power in watts would = 1400. It may not pump a full 100 amps for an extended period, depends on batteries and loads, but hey that's its rating

 

"So is a 100 amp alternator equal to roughly ten 100 Watt Solar panels?"

 

IFFFFF the alternator was at ten volts and 100 amps, that's 1000 watts and ten 100 watt solar panels = 1000 watts. BOTH charge a 12 volt battery so charging voltage has to be greater then 12.6 you know..........

 

Power = V x I so BOTH enter the equation, but you have the idea down...

 

Of course, it takes a decent size motor to run that alternator while the solar panels just sit there in the sun!!!! If I recall 1 HP = 746 watts

 

John T

 

That's pretty cool. So the 100 amps in the alternator is more like 12 or 13 solar panels because it's supposed to be putting out 13.5 to 14.5 volts?

 

I spent about four hours trying to get my alternator out. I was pretty mad at Ford automotive engineers. Eventually I got the old alternator out. OK, well, actually, after three hours I finally called my mechanic and begged him to stop by. I even offered him some of my wife's home made chocolate cake. Half an hour later he came over and pointed out that I was stuck because I hadn't unplugged the regulator. After that it was another 25 minutes of trying to unplug it, but we DID get it out. It looks like it was the original alternator, and it's marked as 75amp. Tomorrow I will pick up the 100amp alternator I ordered from Autozone and hope that I can just plug it in.

 

Back to the excellent electrical lessons,

 

If we use our estimated maximum 4 hours of laptop time and four hours of TV using the "Kill-A-Watt" numbers I recorded earlier, in a given day we have 4 * 10.83 Amps = 43.32Ah

 

The new alternator will provide an "extra" 25 amps. I know it doesn't really work this way because there are so many other variables. If I'm not running every electrical accessory in the vehicle, and we stay on the highway I should in theory have a lot more than 25 amps left over. If I'm driving in a rainstorm at night with all the lights and wipers and the stereo system at lose-your-hearing volume, I might not have the extra 25amps because of complex technical thingies that EE's and EG's (Electrical Geniuses) understand. But I'm going to pretend it's 25 "extra" amps so I can get a vague number to work with when we travel.

 

The alternator is already talking the same volts as the battery, so to "refill" that 43.32Ah would require us to drive for about an hour and 45 minutes, right?

 

I still intend on eventually getting one or two 100W solar panels, but now I know I have a lot of repairs to do first. It will probably be three or four months before I can afford to buy solar panels. if we dry camp somewhere and use four hours of laptop and TV time, but I know I'm going to drive to another location two hours away the next morning, can I leave the generator turned off and just count on the alternator to charge everything back up, or is there some other factor that governs how fast the alternator will charge the batteries so that it doesn't fry them?

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Moon Man, you're really getting into this sparky stuff lol

 

"That's pretty cool. So the 100 amps in the alternator is more like 12 or 13 solar panels because it's supposed to be putting out 13.5 to 14.5 volts?"

 

A typical hooked up to battery alternator may be charging around 14.2 volts or so. At 100 amps that's 1420 Watts. A Solar Panels open circuit no load voltage may be 17 and higher volts, but its what voltage it charges a battery that matters and again that may be 13 to 14+ volts subject to batteries and charge controller. If you use the same voltage (say 14.2) then to arrive at 1420 watts you would be at fourteen.2 100 watt solar panels........BUT THEY DONT NEED TURNED USING A MOTOR OR ENGINE

 

"The new alternator will provide an "extra" 25 amps. I know it doesn't really work this way because there are so many other variables. If I'm not running every electrical accessory in the vehicle, and we stay on the highway I should in theory have a lot more than 25 amps left over. If I'm driving in a rainstorm at night with all the lights and wipers and the stereo system at lose-your-hearing volume, I might not have the extra 25amps because of complex technical thingies that EE's and EG's (Electrical Geniuses) understand. But I'm going to pretend it's 25 "extra" amps so I can get a vague number to work with when we travel."

 

YES the new alternator can produce 25 amps MORE then your old one. Subject to the typical chassis loads (lights, AC, accessories, wipers, fans, charging) I doubt 75 amps is needed for any extended periods of time other then after start up and/or if the battery is very low and if so it may crank out 75 for a time until the battery is charged. What I'm saying is if you have a 100 amp alternator after driving a while to charge the engine battery you may have 30 to 50 amps and more to go to charging the house batteries yayyyyyyyyyyyyyyyyyy

 

"The alternator is already talking the same volts as the battery, so to "refill" that 43.32Ah would require us to drive for about an hour and 45 minutes, right?"

 

If you have drawn 43.32 Amp Hours of energy from your house batteries YES it would take 43.32 Amp Hours to replace that energy. That could be 43.32 amps for one hour or 1 amp for 43.32 hours etc. Again, the alternator can deliver 100 amps, but some goes to engine battery,,,,,,some to chassis loads,,,,,,,some to house batteries and absent a lot of data I cant say for sure how much goes where. It depends on the batteries and loads and resistances and the alternators voltage regulation circuitry. Also I don't envision the alternator sitting there delivering any constant 100 amps for long extended time periods so I WOULD NOT SAY FOR SURE JUST BECASUE YOU HAVE A 100 AMP ALTERNATOR AND ENGINE USED 57 AMPS YOUR GONNA GET 43.32 AMPS CONSTANT INTO THE HOUSE BATTERIES IE DONT BET YOUR LIFE YOU CAN REPLACE 43.32 AH INTO YOUR HOUSE BATTERIES IN ONE HOUR AT 43.32 AMPS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

ALSO its very important that you use heavy gauge and short as possible cables from house to engine battery and a quality low resistance isolation relay to help the house battery charging.

 

ALSO the engines alternator IS NOT any high quality so called "Smart Charger" that may be a 4 stage unit (Bulk, Absorption, Float, Equalize) such as a Progressive Dynamics or Magnadyne etc and isn't going to give you a fast quality smart charge like an expensive 120 VAC Charger. Sure, it will pump amps and energy back into depleted house batteries but never to the quality and completeness a Smart Charger will deliver. Even if I drive all freaking day with my house battery bank in parallel with my engine battery and their voltage at 14.2, when I arrive at an RV park or fire up the genset the Smart Charger will still do its thing to deliver a more complete quality full charge into the house battery bank.

 

SUMMARY you have the right idea and are getting this all down just don't bet your life on my or your numbers above as there are so many unknowns and variables and things never seem to work out as good as the manufacturers specs lol

 

PS if you do your homework and shop solar panels aren't too much over a dollar to 1.5 per watt. I suggest you reserve some of the solar budget towards a quality MPPT smart solar charge controller

which is also very important to complete your solar package. I made that mistake once and Jack and Yarome and WV rat and several fine gents on here enlightened me TAKE THIER ADVICE OVER MINE WHEN IT COMES TO SOLAR DECISIONS Im old and rusty on this stuff

 

John T

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