I am starting to really dislike my camper solar

Hi Dawn
Sounds like you are making head way, with your batteries and charging. I'm sure you know but would like to say this. When you mentioned you keep water in your refrigerator. If you put a lot of warm water (ambient) in at one time this would be a large load on the refrigerator system. It will run till it achieves set point. Take one out and replace with one at ambient at same time would be less of a load. Think of carrying a whole case of water up stairs vs. carrying one or two bottles each time you go up the stairs.

Russ
 
Yep - its the electrical stuff I dont know - that fridge stuff I do know :)

I put frozen bottles in freezer if I dont have food in there (or to take up remaining freezer space), and moved cold water bottles to fridge.
I got all that covered. Researched the heck out of Best Practices early on.
 
Dawn...

12.86V is a good number.

If you want some "put me to sleep" reading material, check out the Victron white papers. FYI, after reading some of this info two or three times, I still only have a 2% grasp of what they are talking about. But, there are quite a few nuggets of info even a blind squirrel could find!

Also, Battle Born Batteries web site has some highly technical, but, very good info.
 
Vic Harder said:
Congrats! I think you might be the first person here to switch from a Trimetric (Which is considered to be a very good PWM controller) to a Victron MPPT.

What kind of difference are you seeing in charging "faster"?
Click to expand...
The charging faster is directly related to the 10-15% higher efficiency of the controller. More power from the solar panels goes into the battery ie less time needed to recharge the battery.
 
"The charging faster is directly related to the 10-15% higher efficiency of the controller. More power from the solar panels goes into the battery ie less time needed to recharge the battery."

============================================================================


My ignorance...but how does a specific "controller" put more power from a solar panel into a battery than any other controller; assuming the capacity of each controller is the same and matches the solar panel output?

Does one controller restrict the amount of energy going into the battery ?

What specifically is the source and process that makes a controller have "10-15% higher efficiency"?

Thanks,

Phil
 
Wallowa, easy answer.

PWM convert voltage over what is needed to heat. So if the panel is putting out 19v the PWM will chop off at say 14v and 5 volts will go to heat. This is why PWM controller all have a heat sink. Amps from the panel will stay the same.

MPPT controller takes the extra volts and converts them to higher amps. The higher amps will charge the battery faster.

Article here.
 
I find it easier for me to think in power (watts)

I’m going to have to make up some numbers for this example

Let’s say your solar panel is 100w panel. This means to put out 100w it’s probably about 17volts at 5.9amps (volts * amps = Watts)

If your battery is needing 14.2 volts to bulk charge a PWM controller will send it 14.2 volts at 5.9amps (83.8watts) a MPPT controller will convert the power at 95% efficiency to 14.2 volts at 6.6 amps (95 Watts)

This is where the added efficiency comes from and where the quicker charging comes from.

Let’s say you have a 100 amp hour battery
That means if you draw 1 amp it will last 100 hrs or 10 amps will be 10 hrs.
If you use 20 amp hours and are charging at 5.9 amps it will take a little over 3.4 hours to recharge. At 6.6 amps it will be a little over 3.0 hours

Disclaimer all these numbers are made up and are approximate

I hope this helps
 
Wallowa, easy answer.

PWM convert voltage over what is needed to heat. So if the panel is putting out 19v the PWM will chop off at say 14v and 5 volts will go to heat. This is why PWM controller all have a heat sink. Amps from the panel will stay the same.

MPPT controller takes the extra volts and converts them to higher amps. The higher amps will charge the battery faster.

Article here.


[SIZE=10.5pt]Good stuff Bill and thanks...honestly after reading and re-reading that article I am a bit confused if any "advantage" with a MPPT over a PWM would be realized with the standard 160w roof panel, even with portable 80w, and my two AGM 12v batteries.[/SIZE]

[SIZE=10.5pt]The MPPT seems geared toward large arrays and high voltages. [/SIZE]

[SIZE=10.5pt]Article starts out by saying most solar panels produce more charging voltage that a 12 volt battery can handle or need. [“[/SIZE][SIZE=11.5pt]Most solar power systems use 12 volt batteries, like you find in cars. (Some use other voltages and the same advantages apply to these systems as well.) Solar panels can deliver far more voltage than is required to charge the batteries.[/SIZE]”]

[SIZE=10.5pt]Then article goes on to say the MPPT takes that "excess' voltage and produces more amps from it but doesn’t overcharge the battery ...confusing to me...volts are nice but amps from panel in my mind are what count...seems that amps are what "fill" the battery with volts "pushing"; how an MPPT can process the "excess" volts from a panel while a PWM can't escapes me..below is a copy of the pro and cons of PWM/MPPT controllers from that article...nothing really clear cut in it that I see; claim of "+30%" would seem to be based on larger solar systems/different batteries than we use in FWCs.[/SIZE]

[SIZE=10.5pt]“PWM Type Solar Controllers MPPT Solar Controllers[/SIZE]

[SIZE=10.5pt]PROS–[/SIZE]​

[SIZE=10.5pt]PWM[/SIZE][SIZE=10.5pt] controllers are built on a time tested technology. They have been used for years in Solar systems, and are well established[/SIZE]

[SIZE=11.5pt]– These controllers are inexpensive, usually selling for less than $350[/SIZE]
[SIZE=11.5pt]– PWM controllers are available in sizes up to 60 Amps[/SIZE]
[SIZE=11.5pt]– PWM controllers are durable, most with passive heat sink style cooling[/SIZE]
[SIZE=11.5pt]– These controllers are available in many sizes for a variety of applications[/SIZE]


[SIZE=10.5pt]– MPPT controllers offer a potential increase in charging efficiency up to 30%[/SIZE]

[SIZE=11.5pt]– These controllers also offer the potential ability to have an array with higher input voltage than the battery bank[/SIZE]
[SIZE=11.5pt]– You can get sizes up to 80 Amps[/SIZE]
[SIZE=11.5pt]– MPPT controller warranties are typically longer than PWM units[/SIZE]
[SIZE=11.5pt]– MPPT offer great flexibility for system growth[/SIZE]
[SIZE=11.5pt]– MPPT is the only way to regulate grid connect modules for battery charging[/SIZE]

[SIZE=10.5pt]CONS–[/SIZE]​

[SIZE=10.5pt]PWM[/SIZE]

[SIZE=10.5pt]The Solar input nominal voltage must match the battery bank nominal voltage if you’re going to use PWM[/SIZE]

[SIZE=11.5pt]– There is no single controller sized over 60 amps DC as of yet[/SIZE]
[SIZE=11.5pt]– Many smaller PWM controller units are not UL listed[/SIZE]
[SIZE=11.5pt]– Many smaller PWM controller units come without fittings for conduit[/SIZE]
[SIZE=11.5pt]– PWM controllers have limited capacity for system growth[/SIZE]
[SIZE=11.5pt]– Can’t be used on higher voltage grid connect modules[/SIZE]

[SIZE=10.5pt]– MPPT controllers are more expensive, sometimes costing twice as much as a PWM controller[/SIZE]

[SIZE=11.5pt]– MPPT units are generally larger in physical size[/SIZE]
[SIZE=11.5pt]– Sizing an appropriate Solar array can be challenging without MPPT controller manufacturer guides[/SIZE]
[SIZE=11.5pt]– Using an MPPT controller forces the Solar array to be comprised of like photovoltaic modules in like strings”[/SIZE]



[SIZE=11.5pt]I am late to the party, but remain a big skeptic since most FWC owners have no issues with the FWC components and system designs. This design has systematically evolved over the years as best as I can tell into a leader in the industry. Someone mentioned that our campers only have "RV grade" components [referring to heater]; our campers are RVs.[/SIZE]

[SIZE=11.5pt]My mantra has and remains that "sophistication breeds vulnerability"; given the choice between an empirically derived and tested system and an "enhanced improvement", I will go with the reliability of simplicity. KISS comes to mind.[/SIZE]

[SIZE=11.5pt]But hey, I could be wrong folks![/SIZE]

[SIZE=11.5pt]Phil [/SIZE]

[SIZE=11.5pt]Ps...Just read Machine's post...a good one, but still doesn't explain how the MPPT produces more amps...bottom line was:[/SIZE]

"If you use 20 amp hours and are charging at 5.9 amps it will take a little over 3.4 hours to recharge. At 6.6 amps it will be a little over 3.0 hours"

So by using the MPPT and not the PWM I will have 24 mins less charging time in the example given; 12% less time. And this is theoretical and more to the point is it significant in the operation of our campers?
 
Both types work. For a large system like on a house, MPPT is the obvious choice. For the smaller RV systems, PWM has been useful for a long time and with solar panels dropping in price, adding another panel would likely overcome the MPPT advantage where it exists.

Starting fresh, I would go with the MPPT system, but I see no economic advantage in tossing my PWM system to install MPPT for the situations where its advantages are compelling. Much better use of limted funds for me would be to replace my inefficient Dometic fridge with one of the more efficient units now available and thus eliminate the need for more charging capacity.

YMMV
PAul
 
PaulT said:
Both types work. For a large system like on a house, MPPT is the obvious choice. For the smaller RV systems, PWM has been useful for a long time and with solar panels dropping in price, adding another panel would likely overcome the MPPT advantage where it exists.

Starting fresh, I would go with the MPPT system, but I see no economic advantage in tossing my PWM system to install MPPT for the situations where its advantages are compelling. Much better use of limted funds for me would be to replace my inefficient Dometic fridge with one of the more efficient units now available and thus eliminate the need for more charging capacity.

YMMV
PAul
Click to expand...
All true. I had a 100w panel with a 30amp PWM. Needed more and it was way cheaper to buy and add a 150w panel than to add an MPPT controller. Worked fine. MPPT controllers are now 1/2 of what they were so if starting fresh I would go MPPT and 24v panels. I added a Victron MPPT only because it was on sale and I like the Bluetooth to my phone so I can see what is happening.
 
A couple of minor points about MPPT solar - unfortunately the article that was linked is both a little out of date and geared towards large residential solar installations.

Quality MPPT and PWM charge controllers now cost about the same for the sort of installations we are talking about on an FWC - so if you were installing a solar system now, you would be silly NOT to use MPPT. For the record FWC has also switched to MPPT charge controllers.

Now if you already have a PWM controller and it is working fine, it would likely not make economic sense to switch it for MPPT. Most people seem to switch from PWM to MPPT for the extra capabilities and features that are built in to MPPT controllers more than for the extra 10 -30% efficiency. The exception to this would be if your space for roof panels is already full (area or weight) and you want more power - MPPT will get you a little extra with no extra weight or area.

Finally, PWM panels aren't actually turning the 'lost' power into heat in the controller - the panels never make the extra power. The key here is that MPPT allows the panels to operate at their most efficient voltage/current combination - yielding the most power. The way MPPT works is that it tries all the voltage/current combinations for the panel every few seconds, and chooses the one which produces the most power.* PWM controllers force the panel to operate at battery voltage, which is usually only 70 - 90% of max power. You usually will see bigger heat sinks on MPPT controllers as the small amount of power lost in these (1- 5%) is actually dissipated in the controller itself.

*It is actually a little more complicated than that, but this will do for now.
 
[SIZE=11.5pt]Ps...Just read Machine's post...a good one, but still doesn't explain how the MPPT produces more amps...bottom line was:[/SIZE]


it it some fairly complex electronics, basically a DC-DC converter.

I don't know the details, and don't need to, it is a black box filled with magic smoke...........................;)

if the smoke comes out it doesn't work any more...........

Sorry if I sound flippant, I work with a lot of stuff I don't know the details, I just make them work.


I would not be chasing the small amount of efficiency if I had an existing system, I would look at my power usage and try to be below what I can get from the Solar in reasonably poor conditions, If I had problems I would add more solar panels.

When I built my system I went wit a big enough MPPT controller I will not have a problem adding panels if needed.
BUT I also learned that my truck has a computer controlled alternator so it is not a reliable high power charging source.

I believe the key is to know and understand the power usage compared to the power generated whatever sources you have.
 
Vic Harder said:
You might want to look at the CTEK D250S DC-DC converter if you haven't already. https://www.ctek.com/products/vehicle/d250s-dual

Bernard (user name here is bfh4n) uses one. The advantages are discussed starting with post #23 here
http://www.wanderthewest.com/forum/topic/13230-i-need-more-power-scotty/page-3#entry154036
Click to expand...
I've looked into them, there is a lot of discussions about them on Expedition Portal.

they are quite expensive, I think I will buy another solar panel first. but it is on the like to have list.

It would be nice to be able to use the truck for a quick charge on a string of cloudy rainy days though.
 
I got the MPPT controller, but haven't been able to install it yet. I thought a friend was going to, but didnt happen. Now I really wish I'd gotten another panel instead. :-(
 
hoyden said:
I got the MPPT controller, but haven't been able to install it yet. I thought a friend was going to, but didnt happen. Now I really wish I'd gotten another panel instead. :-(
Click to expand...
Hey Dawn, are you wishing that because your batteries are now healthy? What's the latest in terms of what the BMV shows?
 
I do not expect anyone to agree but I have no self control and will say it anyway:

Full disclosure: I do not have a solar system or have any experience using a solar system of any kind.

A 100 watt solar panel has approximately 5 amps of production and a deadhead voltage of around 19 volts on a very sunny day with some allowance for dust, less than perfect sun angle, and trying to keep the numbers decimal free.

1) A 100 watt solar panel hooked up to a 6 volt battery with no solar controller and good wiring will send 5 amps to the battery or 30 watts with a good sun exposure (keeping my example simple by ignoring charge state voltage versus discharge state).

2) A 100 watt solar panel hooked up to a 12 volt battery with no solar controller and good wiring will send 5 amps to the battery or 60 watts (keeping my example simple by ignoring charge state voltage versus discharge state).

3) A 100 watt solar panel hooked up to two 12 volt batteries in series with not solar controller and good wiring will produce zero amps since the panels will be "deadheaded".

On a modestly cloudy day, a 100 watt solar panel is capable of producing 4 amps and has a deadhead voltage of 17 volts.

4) On a modestly cloudy day, 100 watt solar panel will send 4 amps to a six volt battery with no controller and good wiring or 24 watts.

5) On a modestly cloudy day, a 100 watt solar panel will send 4 amps to 12 volt battery with no controller and good wiring or 48 watts.

My Ford F-150 alternator hooked up to a 6 volt battery with good wiring and no controller or fuse will produce 130 amps and boil the 6 volt battery or burnout the alternator or both.

The alternator is a fixed voltage device with variable amps.

The solar panel is a fixed amp device.

An MPPT controller goes after what are called "lost watts". In example 1), the lost watts are 95 (19x5) minus 30 (6x5) or 65 watts. In example 2), the lost watts are 95 (19x5) minus 60 (12x5) or 35 watts. In example 4), the lost watts are 68 (17x4) minus 24 (6x4) or 44 watts. In example 5), the lost watts are 68 (17x4) minus 48 (12x4) or 20 watts.

MPPT controllers do not create watts for free. They consume approximately 10% of the input watts to operate. Given the difference between battery charge and discharge voltage and the 10% watts lost across the MPPT controller, MPPT controllers are especially effective above 17 volt deadhead conditions, i.e. getting lots of sun.

MPPT controllers periodically disturb the current/voltage coming from the solar panel to calculate how many watts are available at the current solar level and then do a condition specific DC:DC conversion to convert the unused watts to usable amps/volts for charging.

A very good MPPT controller could charge the two 12 volt batteries in series but at around 2-3 amps from a 100 watt panel on a sunny day.

Expensive but very smart devices.
 
Iowa,

Very interesting..but what is "Deadhead Voltage"... a J. Garcia thing? :D

Also, I may have missed it, but no mention on FWC two 12V AGMs in parallel not series as your example.

Your conclusion on the 'OEM' FWC solar set-up?

You lost me on calculations of net "recovered' 'lost watts'.

Thanks,

Phil
 
"Deadhead" voltage, my term, is the voltage a panel or series of panels will stop producing current. 19 volts is a typical full sun/good sun angel maximum voltage from a panel. Hook up a single panel to a 20 or more volt battery and the panel will produce no current/no charge. Two panels of the same type would "deadhead" at 38 volts in series, full sun/good angle.

One 100 watt panel in full sun with a good sun angle would send 5 amps to two 12 volt batteries in parallel.

One 100 watt panel in modest clouds would produce 4 amps to two 12 volt batteries in parallel.

The concept of "lost watts" requires an understanding that amps and volts can not be arbitrarily converted between each other just because the definition of a watt is volts times amps. A physical device is required to convert amps to volts or visa versa. Many people think that because watts equals volts times amps they can be converted without a device. Watts equals volts times amps is a definition not a law of physics. Saying a solar panel produces a maximum of 100 watts does not describe how a solar panel will charge a battery. The physical properties of the solar panel tell how the watts are produced (volts versus amps) and how a battery will charge.

To simplify, a 100 watt panel is a maximum 20 volt device in full sun (actually 19 volts) and will produce 5 amps at a variable voltage (20 volts x 5 amps equals 100 watts) as a physical property. Note: at a variable voltage. What sets the voltage? The voltage is set by the battery. If the 5 amps goes into a 12 volt battery or two 12 volt batteries in parallel, then the panel is only producing 60 watts (12 x 5). The 40 watts off the rated capacity are "missing" or "lost". MPPT controllers are a physical device for converting volts and amps but at a processing cost of 10% of the input.

The plots of solar panel performance (physics) are almost linear for a large voltage range and then curve as they approach "deadhead". I simplify. I like 100 watt panels, 20 volts, and 5 amps for the simplicity of illustration.

As for the FWC OEM solar system: too much variability from one user to another to comment. I have met FWC Granby's with two way refrigerators and no solar panel who can camp for 3 days without starting the truck and stay in the battery operating range all the time. How big is the trucks alternator and how is the voltage regulator calibrated? How good are the wire connections at each junction between the truck battery and the camper? What is outside temperature? Now add a solar panel and have the alternator and solar panel argue over voltage. Put a fancy monitor in the mix and all the current flows will change because of the monitor (law of physics, simply looking changes everything).

My own design point for solar is to expect 25 amp hours per day at the 12 volt batteries per 100 watts of roof solar average between April 1 and November 1 in the lower 48 states (someones published calculation) without an MPPT controller. Engine alternator current only significant on cloudy days and between 4pm and 9am. 130 amp alternators and larger work well at charging. Smaller sized alternators will work on a case by case basis.
 
Damn...nice information..thanks...you say that for the mix of watts/amps/volts you "need a device" before the equation Watts=Amps x Volts is accurate and that the equation is not immutable; not "a law of physics"....but a variable expression...wow...that blows right by me!

My question concerning FWC solar system was not addressing the adequacy of that system for any individual user but how efficient is the FWC solar system at capturing and storing energy...in short is the FWC solar a "good" system? Or does it need tweaking to meet what would be considered the nominal power use in a fully equipped camper given a power production and storage such as you delineate in your last paragraph?

Thanks for your expertise and patience....interesting topic; if only academic.

Phil
 
You must log in or register to reply here.

Similar threads - WTW

R
Rear solar SAE port
Deancamp
D
Z
2006 FWC Electrical Issue
Wandering Sagebrush
Wandering Sagebrush
J
Circuit Protection in Typical Camper Power Systems
Jon R
J
W
Q for this still running their old Atwood heaters
Saturn949
S
K7MDL
Installed Renogy One Core monitor and Battery Shunt 300
K7MDL
K7MDL

New posts - WTW

Back
Top Bottom