How to connect an alternator to my vans solar system

SaraAnarchy88

Hi I have a 97 Dodge Ram Van 3500 that I've been slowly converting. I got a pv system from Renogy and was wondering how I can connect my alternator to my pv system. I have three 100 watt Renogy solar panels (hopefully soon 4), a 40 amp mppt Renogy charge controller, a Vmax 175 ah AGM battery and a 2000 watt Renogy pure sine inverter. I'm new to all this so I really appreciate your help thank you!

BB.

Are you going to have two different battery banks (one to start the van, a second for the "house" power)?

The typical method is to get a relay (or electronic relay/diode battery isolator) that only connects the two battery banks together when the alternator is charging:

http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias=automotive&field-keywords=battery+isolator&rh=n:15684181,k:battery+isolator

There are also various DC to DC battery charger options... Here is one:

http://www.xantrex.com/power-products/power-accessories/auxiliary-battery-charger.aspx

There are pluses minuses with each type.

-Bill

SaraAnarchy88

Awesome! Thank you! If I understand correctly the battery isolator is what I'm thinking. Do I connect the isolator directly to the house battery or the charge controller? What are the cons of this type of system? Thank you so much for your help your the best!

BB.

The isolator is simply connected (with the correct size wiring) between your two battery banks. The simple version is just a heavy electrical relay that "turns on" at ~13.x volst and turns off at ~12. volts.

When the alternator is charging, both battery banks are connected together (in parallel). Note that (especially) for 12 volt battery systems, you need heavy wiring to carry the current and keep the voltage drop low. Ideally, you want about 0.05 to 0.10 volt drop because of the copper wiring. And that is one weakness--Heavy/expensive copper cable + long(er) wiring run from the vehicle battery to the house battery bank--Of course, in a van, hopefully that is not a very long run.

Another issue--Most car type alternators while rated for >100 Amps--Typically get hot pretty quickly when supplying high current, and frequently will drop down to much less than 50 Amps (guessing) when charging. So--Using the stock vehicle alternator setup may supply less than expected charging capabilities. And idling the vehicle engine can use a lot of fuel and exhaust fumes can be dangerous (if you are sleeping in the vehicle).

If you are driving a lot (every few days)--The vehicle alternator can be used to supply a significant amount of your house power... However, if you drive 20 minutes and park for 2 weeks--Then the alternator becomes less useful (in general). And you need to look at other options (lots of solar panels, Honda or Yamaha 1,000-2,000 Watt genset, etc.).

My suggestion is to start with your loads (how many watts * hours per day of usage), How many days of dry camping at a time. Seasons of use, Approximate location, etc.

Most RV solar applications start with plastering the roof with solar panels (what will fit). Then design the battery+inverter+etc. system around the amount of power the panels can supply. In some cases, RV's are battery limited--weight and space--And that is where we start the design. Then--Whatever power the solar system can supply is what you get. Make up any extra power needs with running the vehicle engine and/or AC genset.

in the end, solar panels and batteries usually supply much less power than most people would expect to use (charging laptop computer, lights, fan, etc.). Until you know your loads and energy usage--It is very difficult to design an off grid power system to support your needs. We are just guessing.

-Bill

SaraAnarchy88

Wow Thank you so much! You've helped me out more then you know. I think your right I need to put up my solar panels first and see where I stand from there. Still I appreciate you taking the time to explain all this to me. You've given me what I need to think about until the time comes

BB.

We can do the basics, without you spending any money.

Look up some solar panels and see how many you want to fit on your rv. Then we can size your battery bank and predict the basic loads the system can supply.

There are Vmp~18 volt panels which can change 12 or 24 volt battery bank's with inexpensive PWM type solar controllers. Vmp~18 volt panels are usually smaller and may fit your roof space better.

If you go with Vmp~30 volt or other panels, you typically more expensive MPPT type solar charge controllers. Vmp~30 volt panels can be much cheaper. So, it can be a balancing act.

Do the paper design first. You can save lots of expensive mistakes.

-Bill

SaraAnarchy88

Yeah I'm a little worried that I already bought all that stuff I mentioned. I guess the only thing I'm really worried about is needing more power then being supplied but then again I'm in the van a good amount right now and doing just fine. I'd just like to be able to charge my phone easier, have some light to read at night and a mini fridge so I don't have to buy ice every couple days

BB.

Mini fridge can be the killer. They can use a lot of electricity. Why many people use propane refrigerators.

-Bill

BB.

What solar panels? How many.

What batteries? Voltage and AH rating?

What ac inverter?

What solar charge controller?

-Bill

SaraAnarchy88

I have three 100 watt Renogy solar panels (hopefully soon 4), a 40 amp mppt Renogy charge controller, a Vmax 175 ah AGM battery and a 2000 watt Renogy pure sine inverter.

I just thought of another question. With the battery isolator do I need to install fuses?

BB.

r400 Watt of solar panels and 5% to 13% rate of charge for battery bank will support:

• 400 Watts panels * 1/14.4 volts charging * 0.77 panel+controller derating * 1/0.05 rate of charge = 427 AH @ 12 volt maximum
  
• 400 Watts panels * 1/14.4 volts charging * 0.77 panel+controller derating * 1/0.10 rate of charge = 213 AH @ 12 volt nominal
  
• 400 Watts panels * 1/14.4 volts charging * 0.77 panel+controller derating * 1/0.13 rate of charge = 164 AH @ 12 volt minimum

If you use 50% of the battery capacity, you will get:

• 175 AH * 12 volts * 0.50 discharge * 0.85 inverter eff = 893 Watt*Hours of "useful" stored energy

Say you want to use the power over 5 hours:

• 893 WH of stored energy / 5 hours of use = 179 Watt average AC load
  

Lets say you camp around southern California:

http://solarelectricityhandbook.com/solar-irradiance.html

Bakersfield
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan	Feb	Mar	Apr	May	Jun
2.61	3.55	5.09	6.50	7.49	7.99
Jul	Aug	Sep	Oct	Nov	Dec
7.71	6.93	5.81	4.44	3.10	2.51

And you camp 9 months of the year... Giving you February as the "break even" month:

• 400 Watt panels * 0.52 typical off grid system eff * 3.55 hours of sun per day (Feb) = 738 WH per day (average Feb)
• 400 Watt panels * 0.52 typical off grid system eff * 5.09 hours of sun per day (March-Sept) = 1,059 WH per day (March-Sept)
  

So--For the most part, your system is pretty well balanced. And 300-400 Watts of solar panels will work nicely.

The one big issue I have--Your 2,000 Watt inverter. Notice that if you use your inverter at rated output (2,000 Watts), you will use up a day's worth of sun in 1/2 an hour. Also, 2,000 Watts is a pretty heavy load for a 175 AH 12 volt battery (AGMs are better at supplying high current--But still a lot of current). To support 2,000 Amps @ 12 volts, the fuse/breaker/wiring would need to be rated at (minimum):

• 2,000 Watts * 1/0.85 inverter eff * 1/10.5 volt cutoff * 1.25 Fuse/Wiring derating = 280 Amp rated circuit

My suggestion--Unless you really need that large amount of AC power (for a short period of time)--I would highly suggest a much smaller AC inverter. The MorningStar 300 Watt 12 volt TSW inverter would be a much better fit (plus it has remote on/off input, search mode).

That would be the one big change I would recommend. A 2,000 Watt AC inverter can use 10-20 Watts (or more) just "turned on" (Tare Loss). The MorningStar runs at 6 Watts, or much less in "search mode".

Yes--All wiring that leaves a battery + terminal should be fused/breakered to protect wiring against short circuits. Here are a couple of charts that you can use to size the protective devices. NEC is quite conservative. The ABYC chart is much less conservative:

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
http://www.acbsphl.org/Tips_and_hints/ABYC_Wiring.htm

-Bill

SaraAnarchy88

Oh my gosh you are the best! Ok great that takes a lot of my worry away! Smaller inverter. That one you suggested looks really nice. It even has a remote control nice! Thank you so much you've helped me so much I can hardly thank you enough!

BB.

You are very welcome Sara. Let us know how it all works out for you.

-Bill

oil pan 4

If the panels lay flat they will only put out about 40 to 50% of rated watts in winter and maybe up to 60% in summer.

Also the vehicle alternator system is not designed to charge all those batteries. The alternator will run at full load for extended time, that will likely over heat everything in the system until something burns up. First thing to go will likely be the alt to battery wire, then the rectifier diodes and if those don't burn up it will scorch the alternator stator windings.

This is how I am updating the charging system to be more efficient and handle running at full load.

http://ecomodder.com/forum/showthread.php/schottky-diode-alternator-33199.html

papab

I don't know the capacity of the alternator in your van, but I think oil pan overstates the risk.  The alternator will only run at full load if the battery is really low, <50%.   Yes, make sure the cable is big enough to handle the load.    I know in my campervan with a 150 Ah AGM it draws about 50 amps at 60% state of charge and it drops fairly quickly as the battery gets charged up.   
Try to get everything you need on 12V, not 110AC, it will be much more efficient.   I have a 4.3 cuft 12V fridge (that's big for a campervan), a 100 W folding, portable panel and I get back to 100% everyday if I'm camped & the sun is shining.   

oil pan 4

I have burned a alt to battery wire off the alternator so I know what I am talking about.

If the alternator is upgraded to a larger one and nothing else changed you will fry some wiring.

bill von novak

oil pan 4 said:

>If the panels lay flat they will only put out about 40 to 50% of rated watts in winter and maybe up to 60% in summer.

Depends on your latitude.  The more South the less power you lose from off-angle losses.

> First thing to go will likely be the alt to battery wire,

Well there's your first problem right there.  You connect the new battery wire/isolator to the post on the alternator, not to the old battery.

oil pan 4

I have panels, I am in New Mexico and this winter they were producing between 40% and 50% of rated going to a Morningstar MPPT charger controller.

I didn't have solar when I burned the wire off the alt the first time. That was factory configuration just from charging two group 34 batteries that were low on power from starting the cold diesel engine.

To tie vehicle solar in the vehicle I just hooked the charging wire up to the fusible link on the fire wall.

scrubjaysnest

In 3 decades of charging house batteries via the tow vehicle alternator I have never had an alternator fail. A couple of notes on this, batteries were never larger then grp 27 and isolation was always solid state vs relay. Our current set up is a 125 amp alternator feeding the isolator through the fuse able link.
If the "wire burned off the alternator" this could have been the result of a bad crimp. Most failures with high DC currents that result in "burned wire" are the result of poor connections. That doesn't mean there are others.

BB.

And, in general, it is pretty difficult to pull large amounts of current (100 amps+) vs the 10-20 amps or so that the long cable run at 12 volts generally supports (voltage drop from long cable runs) wnen batteries are mounted in a towed vehicle.

-Bill.

Dave Angelini

Definitely Bill ,  but there are the Balmar hot rated alternators that have 250 amp ratings that I use to use on Yachts and Power boats.
I have seen some of those big RV's using them.
Kind of makes you want to check torque on a monthly basis......

BB.

Balmar and possibly some others (as I recall) also can have remote voltage sense leads. Attach the sense leads to the battery and the alternator will output higher voltage to make up for the voltage drop in the wiring--But that is two extra wires that need to run back to the alternator/charge controller.

-Bill

Dave Angelini

And that is where the saying "there is always another wire"  comes from!  

scrubjaysnest

BB. said:

And, in general, it is pretty difficult to pull large amounts of current (100 amps+) vs the 10-20 amps or so that the long cable run at 12 volts generally supports (voltage drop from long cable runs) wnen batteries are mounted in a towed vehicle.

-Bill.

This is for sure; it's also the reason I paralleled the 10 AWG feed in the camper with another 8 AWG pair. For the Tow Vehicle, TV, I added a seperate feed from under the hood to the new parallel feed in the camper. At the same time I ran a new feed from the TV to the Bargman connector replacing the 22 AWG TV charge line. With a TV and camper you can easily be looking at a 40 foot round trip from tongue mounted battery to the TV engine compartment. For us with the batteries in the very back it's ~80 foot round trip. A long road to push 15 or 20 amps. That is also enough current to develop enough heat at a poor crimp or splice for burned wires at the connection.