Why use solar if the alternator is giving off 70 amps?

[sephiro499]

I'm not against solar I just found this post really interesting and if you drive regularly your batteries would be charged.





http://www.solarpaneltalk.com/showthread.php?15277-Dodge-Caravan-mini-RV-conversion

post #4



"OK lets forget solar and think vehicle alternator. Alternators are rated in Amps. I do not know how many amps your alternator produces but I can safely say at least 70 amps of charge current and likely more. You have to find that for yourself because I am not going to do your work. So if you use say that 360 watt hours each day, and we know the battery voltage is 12 volts then we know you would use 360 watt hours in a day / 12 volts is 30 Amp Hours. Taking into consideration battery charge efficiency of 85% your vehicle alternator wound take 30 Amp Hours / .85 / 70 amps = .5 hours or 30 minutes to recharge. Keep in mind you can go 2.5 days between charges if you have a 150 ah battery. If you went 2.5 days would require you to idle or drive roughly 90 minutes every 3 days.

Now do some rework. You want two 6 volt golf cart batteries. Golf cart batteries are rated around 200 to 240 Amp Hours. So that is a capacity of 12 volts x 200 amp hours = 2400 and 2880 watt hours respectively. If you use 360 watt hours per day you can go about 4 days to reach 50% discharge before having to idle or drive 2 hours to recharge.

So mow you have an idea of what it will take. Do you have the funds and room on your van to hold a 200 watt panel, and 15 amp MPPT controller. Just the panel and controller will cost you north of $400, plus another $250 for batteries. I seriously doubt you have room to mount two hundred watt of solar panel and would look pretty silly making you target for theft. You gotta decide. One other option I did not mention is a hybrid system where you use a small say 50 watt panel and a Battery Isolator. Panel would only supplement the alternator cutting fuel cost."

 

[user 423]

The "IF" can make all the difference. I've traveled a lot this summer and my batteries stayed charged, no problem. This winter I plan on being parked either at QZ or Slab City for 4 months and will hardly ever drive my van. For groceries,water,laundry,visiting,etc. I will ride my little motorcycle that gets 85mpg. So a solar setup is in my future.

 

[SternWake]

People really like to do a little math and think that everybody else is an idiot.

The guy in that post does not take into account a few things.

-Alternators get hot and cannot meet their rated output, if they ever could.
-Batteries can only accept large currents when depleted under 80%
-103 to 150% of the energy removed from the battery must be returned before the battery reaches full charge
- going from 80% to 100% State of charge can take 3x as long as from 50% to 80%, no matter how big or shiny or expensive the alternator is, or the claims of its manufacturer
- An alternator will likely never meet its rated output in a vehicle. the stock cabling is incapable of passing it, the batteries might not ask for that much, and under hood temperatures, including the incredible amount of heat the alternator itself can make, reduce the ability of the alternator to make power.

Alternators are very capable Bulk chargers, if wired properly( thickly). I recommend all and every charging source be deployed to get the batteries to, and jeep the batteries at, the highest state of charge as possible.

However at the 80%+ range a battery cannot accept large currents, and hours and hours can be needed to get the battery in the 95%+ range. The higher the state of charge the battery returns to after every discharge cycle, the longer the battery will last and the better it will perform during that increased lifespan.

By all means, use the adequately cabled alternator to bulk charge, but don't drive that extra 300 miles in an attempt to get the alternator to fully charge a depleted battery. That last 20% is where solar really shines.

And do not believe 90% of what you read on forums concerning Lead acid battery charging. So much is just incredibly misleading and does not take into account so many factors which simply cannot be ignored in real life.

 

[sephiro499]

People really like to do a little math and think that everybody else is an idiot.

The guy in that post does not take into account a few things.

-Alternators get hot and cannot meet their rated output, if they ever could.
-Batteries can only accept large currents when depleted under 80%
-103 to 150% of the energy removed from the battery must be returned before the battery reaches full charge
- going from 80% to 100% State of charge can take 3x as long as from 50% to 80%, no matter how big or shiny or expensive the alternator is, or the claims of its manufacturer
- An alternator will likely never meet its rated output in a vehicle. the stock cabling is incapable of passing it, the batteries might not ask for that much, and under hood temperatures, including the incredible amount of heat the alternator itself can make, reduce the ability of the alternator to make power.

Alternators are very capable Bulk chargers, if wired properly( thickly). I recommend all and every charging source be deployed to get the batteries to, and jeep the batteries at, the highest state of charge as possible.

However at the 80%+ range a battery cannot accept large currents, and hours and hours can be needed to get the battery in the 95%+ range. The higher the state of charge the battery returns to after every discharge cycle, the longer the battery will last and the better it will perform during that increased lifespan.

By all means, use the adequately cabled alternator to bulk charge, but don't drive that extra 300 miles in an attempt to get the alternator to fully charge a depleted battery. That last 20% is where solar really shines.

And do not believe 90% of what you read on forums concerning Lead acid battery charging. So much is just incredibly misleading and does not take into account so many factors which simply cannot be ignored in real life.

Thank you for clarifying all of that information. I have no electrical experience but an adhesive solar panel, charge controller, and batteries I think I can manage on my own. Does having a 'hybrid system' with the alternator make it taht much more complex? I'd probably have someone install the isolator dioode and drill through the firewall since the latter part I've got no idea how to do.

 

[Reducto]

1) The alternator only gives off that much when it's spinning fast so you have to actually be driving to charge the batteries at a decent rate. At idle they generally don't put out very much.

2) The battery will only take so much current at once, to get fully charged it needs lower currents for a longer period of time.

3) Unless you're already in a position where you will be driving 1+ hours per day you'll wind up coming up with excuses to do extra driving and spend a lot more than $400 on extra gas and wear and tear over the life of the panel.

4) I've never had any theft attempts and I've only ever heard of it happening to a vandweller once. There are plenty of panels mounted on remote signs and such for thieves to target if they were so inclined.

I've done the alternator-only thing myself and it was fine when I was on a long road trip but as soon as I stopped for a couple of days I ran into problems and eventually killed my batteries. My alternator went out too - it didn't like running at max current.

 

[freenez2]

Am all for the benefit of an alternater as a charge source. However... I camp for weeks at a time without starting the engine and depend not only on solar to keep house batteries charged, but the starter battery as well. Why fire up the engine and burn gas when solar does it all?

 

[Van-Tramp]

Yup, a car alternate will never charge a deep cycle battery to 100%. It helps, but it is not the answer. Plus, a car engine is a very costly and inefficient generator. It would be better to buy a small 1000 watt generator and run it for 90 minutes as opposed to your engine. I can't believe someone would actually recommend the use of a car alternator over solar.

As noted above, the extra wear on your alternator may end up costing you more headaches than it is worth.
Also, the more friction generated inside your alternator, the worse your MPGs while driving. So, to save a few hundred in solar you are looking at a few hundred in a new alternator (sooner) and a few extra pennies in gas each and every mile you drive... until you finally cave and buy the solar anyway.

If you are going 2 days between charges, you do not use enough power to justify a 200 watt 2-battery system anyway. You could get by with 50-100 watts, 7 amp controller, and a single battery all for under $200.

 

[sephiro499]

I've done the alternator-only thing myself and it was fine when I was on a long road trip but as soon as I stopped for a couple of days I ran into problems and eventually killed my batteries. My alternator went out too - it didn't like running at max current.

I was concerned about the additional strain as well.

 

[christine]

My answer would be that I know nothing about alternators, and I'm pretty sure that charging off the alternator wear it down more quickly. I don't want to have to replace my alternator, because if and when it fails, it'll be in the most inconvenient place at the most inconvenient time, my cell phone won't have a signal, etc. I'd rather spend a little extra money on a solar setup that is separate from the alternator. It's reliable (if the sun is out), and if it fails I can still drive my vehicle.

 

[highdesertranger]

well I think you got your answer. I say have your alternator help out(why not). but don't depend on it. a v8 generator isn't very efficient. highdesertranger

 

[BigT]

I'm glad I found this thread. I was just going to ask if I should stop looking into solar to charge a single 12V 80 to 92Ah AGM of a 160W panel on my van.
Looks like I found my answer.

Now I can get back to the frustrating and headache-inducing task of figuring out what charge controller to get.

 

[GotSmart]

How many amps, and what price?

I recently got this one from Renogy, and am extremely happy.

http://www.renogy-store.com/30-amp-charge-controller-LCD-display-p/ctrl-pwm30-lcd.htm

 

[ZoNiE]

Not a lot of value stealing a single panel. A lot of work, risk, for what? $10-20 on Craigslist? Unless the thief wants the panel itself, there is no ROI for him. No copper to speak of. They are more likely to cut and pull as much wire out of the hole in the van than steal the panel.

One nice thing about 6V GC2's, some thieves are smart enough to notice that they are 6V and will ignore them. Of course, my thieves CUT the wire BETWEEN the two batteries BEFORE they figured that out. :dodgy:

I have them in a Horror Fright Tongue Box with locking hasps now.

 

[jimindenver]

I've told sunking that joke gets better and better every time he tells it, especially when it's to some one like me with a trailer. That tiny wire in the 7 pin is going to deliver all those amps over that distance....They need to sell what he is smoking in Colorado, not weed.

If you travel a lot, an alternator is a wonderful charging source but you still need the long term slow charging that shore hook ups or solar provides. Park for weeks like I do and running the truck or a generator daily becomes annoying. My solar may not produce as much as a alternator at max but it can produce 50 amps all day. Most of the time the batteries are in float, accepting very little while the panels cover the daily loads. In bad weather I'd run the generator long before I'd run the truck. Even then it would be through jumper cables, not the 7 pin.

 

[GotSmart]

I went on the Renogy site to do some research, and most of the answers are from their techs.  Extremely professional, but they only talk about their brand.   It is a good place to get tech answers during business hours.  


I think I will talk to Charlie about that.   :idea:  

 

[BigT]

How many amps, and what price?

I recently got this one from Renogy, and am extremely happy.

http://www.renogy-store.com/30-amp-charge-controller-LCD-display-p/ctrl-pwm30-lcd.htm

Thanks, I saw that you bought that on another thread.  Looks nice.  
Recently someone suggested that since I'm only running a single 160W panel, I might want to go with a MPPT charge controller because they allow more of the power from the panel to reach the battery than a PWM does.  I've also read that PWM's can create interference in radios with the sharp pulses they generate. 

Bob makes a very good point, though.  (I'm going to coin this a bit since I don't remember his exact words).  
"A decent system you actually use is better than a perfect system you merely talk about."

I'd like to run 200 Watts of solar, but I simply don't have the room on the roof of my tiny Transit Connect.  That's why I've opted for a single 160W panel from Grape Solar.  It's the most power in the smallest size I can find.  

The plan is to run a single 160W panel to a 12V 80 to 92Ah AGM battery.  That way I can keep the 2:1 Solar-Watts to battery Ah capacity ratio that comes so highly recommended.  

Recently I've been looking at this charge controller, though I'm not sure if 20 Amps will be enough if/when I double my panel Watts.   http://www.renogy-store.com/20-Amp-MPPT-Charge-Controller-p/ctrl-mppt20.htm

 

[GotSmart]

That is also a good choice. It is a better unit, but more money for only 20A. I do not have any radio interference, but a huge storage battery bank. 448 AH. and just one 100A panel. My Alternator has been tested at 130 amps.

 

[jimindenver]

On the Renogy controller, that is last years Tracer rebadged. Tracer has an improved line out this year that may cost the same.

 

[blars]

Both PWM and MPPT controllers can put out radio interference, more likley on cheap ones that fake the FCC label than ones that actually went through the FCC testing.

 

[sprintersnale]

We use a combination of a bigger alternator with increased charging capacity (150 amp) with isolator switch and one solar panel/charge controller. With 4 AGMs, we can go 4 or 5 days without driving to recharge. Everyone's usage and needs will vary. We arrive at camp fully charged...then park in the shade... :huh: