Anyone familiar with using Renogy Solar Kits?

[PlethoraOfGuns]

Hmmm, maybe there really something about not being to hook up two system like that to the same battery. Like some have stated, the charge controllers are getting false readings from one another and not bulk charging. "Dueling dual controllers."

I have all Victron equipment. I have 600watts of solar on roof wired in series going to MPPT charge controller. I also have 30amp dc to dc charger. They both go to the same 12v LiFePo4 battery bank. While driving with good sun I can see on my battery monitor that the battery is getting like 50amps of input, and both chargers say they are bulk charging at roughly 25amps each. Why don't I have "dueling dual controller syndrome"?

Super smart solar component people please chime in. Is this "dueling dual controller syndrome" really a thing sometimes? I can only think that it may be a factor with lead acid and not LiFePo4?

 

[Freelander]

I want to thank everyone for all the responses and information.  And to end this thread I would like to add one more thing about all this.  

I now have my Renogy 200 watt Eclipse Suitcase Solar Panel Kit and have been testing it out.  It is charging my battery and appears to be working correctly.  However, it takes the same amount of time to bring the battery back to full as did my 100 watt Renogy suitcase kit.  I would have thought that since I doubled the wattage that it would cut the charging time in half.  I go through the same routine every day so I have a pretty good cage of the time it takes, and how my battery power that I use so this just doesn't make sense to me.

What do you all think?

Are you running both at the same time??

 

[PlethoraOfGuns]

Yep. 25amp from alternator and 25amp from solar I can get 50amp of bulk charge.

 

[Van on 66]

Are you running both at the same time??

No.  Needless to say I am disappointed.  A 200-watt solar panel should cut the charging time in half over a 100-watt panel.  So with that said, I shipped the 200-wat panel back.   There definitely is no need in paying $500.00 for something that is giving me the same results as what I am using now.

 

[Cammalu]

Ask JiminDenver he knows everything

 

[Spaceman Spiff]

There are a couple of pieces of information we need:
 - what battery chemistry do you have?  FLA/AGM or Lithium or something else?
 - how do you determine battery state of charge?
 - how do you measure how much current is flowing into the battery?

For lead acid batteries:
A LA battery at 50% charge will accept a maximum of 25 amps per 100AH battery size.
This occurs until the battery reaches about 14.6V.
This will probably drop to 20A as the battery heats up.
It will hold at this charge until the battery reaches  about 80% charge.

At 80% the amount of current the battery will accept will drop from 20A to about 1A over the next 2 to 4 hours.
The charger voltage is held at about 14.6V.
It doesn't make any difference how big a charger you have, the battery will not accept more.
It takes 2 to 4 hours (or longer) to finish charging the battery.

When the charger determines the battery is full it will drop the voltage to about 13.2V.
This is just to keep the battery from self-discharging.
The current flow is usually around 0.1A.

I know this doesn't directly answer your initial question but until we know what we are dealing with we are just guessing.
If your batteries are lithium someone else will have to chime in.  My experience is with lead-acid batteries.

 

[GotSmart]

As long as the controller is properly working, it passes 12(+-) volts into the positive post of the battery. Not counting fuses. You can have as many as you want. 

Wire size and length matter. 

If you drain X power from a battery bank, it will take X power to replace. The system works on 100 watt . 200 will not speed up the replacement rate that the BATTERY needs to function properly. Now if you double your power use, battery capacity and panels, it still would only take the same amount of time to charge.   Charging is a constant at 12 volts depending upon the wire. 

When I started out, I had 400 ah of battery being charged from my alternator. Then one panel, and then another 100 so 200 w panels and 400 ah battery. 

If you want to cut your charging time down, increase your battery bank. Install quality wire sized to fit

 

[Freelander]

No.  Needless to say I am disappointed.  A 200-watt solar panel should cut the charging time in half over a 100-watt panel.  So with that said, I shipped the 200-wat panel back.   There definitely is no need in paying $500.00 for something that is giving me the same results as what I am using now.

I think those kits like use a PWN controller, and as such will throw away any excess wattage from there panels. Now if in stall a 30 amp MPPT controller and did away with the built in controller you would see an increase in charge. My 400 watt system I have seen 300 watts of power from it. A little over 20 amps of charge.

 

[StarryNights]

Suspect you could have a problem with mixing solar panel sizes/wattages. Link to quick Will Prowse explanation: . More detailed link:

Would be interesting to see output of just the new panel.

 

[PlethoraOfGuns]

To clear things up, we are talking about mixing multiple solar charge controllers onto the same battery. I don't think anyone is mixing different panels onto one solar charge controller.

 

[calico]

I always thought current (Amps) is the determining factor in how quickly batteries are charged over power (Watts)?

 

[Calaverasgrande]

I am not familiar with the exact models of charge controller that comes with those panels.
But my Renogy DCC50S MPPT controller uses feedback from the battery to determine how much current to send.
It is certainly possible that two different controllers hooked to the same Negative and positive terminals could interfere with each other.
I see it kind of like driving a single loudspeaker from two amplifiers.
Except in this case the charge controllers use variances in voltage to determine the charge state of the battery bank. When a bank nears it's lower limit the voltage drops by a fraction. When it's near full the voltage is a fraction higher.
If two sources are feeding voltage (and presenting resistive loads), how are the sources to know there is a second source of voltage? They may see a higher total voltage though the battery is still at less than full. So they initiate slowing down the charging, by limiting voltage, current or both.

As hinted above there is also the resistive factor to take into account.
Ohms law concerns more than just volts and amps. The 3rd leg of the stool is resistance.
Not sure what effect the source resistance of each charge controller has on the total load seen by those controllers. I'd have to test mine out of circuit to make an educated guess. But common DC practice is for source impedance and load to be equal.
Whenever a source of power with a fixed output impedance such as an electric signal source, a radio transmitter or a mechanical sound (e.g., a loudspeaker) operates into a load, the maximum possible power is delivered to the load when the impedance of the load (load impedance or input impedance) is equal to the output impedance. In this case, maximum power transfer occurs when the resistance of the load is equal to the resistance of the source.
So if charge controllers are 200 ohms (just spitballing with that number) and the battery load is 200 ohms. They will see a different load depending on how the wiring is done.
In series they would see 400 ohm. In parallel they'd see 100 ohm.
This affects the wattage, as at higher resistances watts go down, at lower they go up.

Of course this is just coffee fueled speculation on my part. But I'd like to hear from an upfitter or solar expert on the wisdom of running tow charge controllers on one bank.
It would seem the correct thing would be to find a way to wire all the panels off one controller.

ps, my area of expertise is in AC audio electronics, apologies if my terminology is a little imprecise here and there. Or if I muddied the waters. But in general Ohms law is Ohms law.

 

[B and C]

From my understanding of charge controllers, if they are set with the same parameters, they will play nicely with each other.

A depleted battery cannot be brought to full voltage immediately. A controller will deliver full amps to the battery until the battery voltage can get to ~14.*VDC. This is called bulk charging. Once it has reached the set voltage (~14.*) it goes into absorption charge. This is where the voltage is held constant and the amps into the battery start to taper. When the amps taper to about 0.5C (battery capacity) amps, the system goes into float mode and the battery is considered fully charged at this point.

 

[Van on 66]

Hmmm, maybe there really something about not being to hook up two system like that to the same battery. Like some have stated, the charge controllers are getting false readings from one another and not bulk charging. "Dueling dual controllers."

I have all Victron equipment. I have 600watts of solar on roof wired in series going to MPPT charge controller. I also have 30amp dc to dc charger. They both go to the same 12v LiFePo4 battery bank. While driving with good sun I can see on my battery monitor that the battery is getting like 50amps of input, and both chargers say they are bulk charging at roughly 25amps each. Why don't I have "dueling dual controller syndrome"?

Super smart solar component people please chime in. Is this "dueling dual controller syndrome" really a thing sometimes? I can only think that it may be a factor with lead acid and not LiFePo4?

Again, thanks for all your input.  All this has been quite a maze for sure, but in the final analysis I have come down to this.  My 100 watt solar system has worked for me so I am going to continue with it.  And with that said, I have come to the thinking that instead of looking for more power, I am better off investing in things such as a spare battery for my laptop and a fairly powerful power station such as a Jackery for when I do have cloudy days.  I will also add an additional battery as insurance even though right now, given my usage, it is also enough.

 

[jimindenver]

Hmmmm

Spare batteries have to be recharged at some point in time and 100 watts of solar isn’t a lot of power.

In any event multiple controllers can be run as long as it was put above they are set the same and they see the same battery voltage. That last part is important for even single controller systems because if the controller can’t see the battery voltage properly, it can’t charge it properly. It can be a issue when you have a cheap controller out with portable panels on a long thin set of wires. It can also be a issue with expensive controllers that don’t have a voltage sensor or voltage sense lines connected.

 

[frater secessus]

I have been told you cant run 2 controllers at the same time unless they may to do that.

Multiple charging inputs works fine.

I can't think of any reason why the battery would care if amps come from one or two different solar charge controller.

Edge cases to consider:

• multiple charging sources exceeding recommended charging current for the battery bank
• controllers relying on trailing amps to exit Absorption may fall to Float prematurely

it takes the same amount of time to bring the battery back to full as did my 100 watt Renogy suitcase kit. I would have thought that since I doubled the wattage that it would cut the charging time in half. I go through the same routine every day so I have a pretty good cage of the time it takes, and how my battery power that I use so this just doesn't make sense to me.

Lithium will charge in less time, assuming we aren't bumping into the max charge rate.

Lead chemistries (including AGM and gel) take the amount of time they take to fully charge, and even connecting a nuclear power plant to them wouldn't charge them (significantly) faster. Lead typically takes 5+ hours to fully charge.

Having said that, there are real benefits to reaching the minimum recommend charge rate for lead banks. Typically 0.1C for flooded (10A for a 100Ah battery) and ~0.2C (~20A for a 100A batt) for AGM. Additional panel means you are also getting effective charging earlier in the day and can support heavier loads.

Edited to add: insufficient charging is the primary cause of death for lead-chemistry batteries.

 

[Calaverasgrande]

Was just watching Will Prowse doing a comparison of charge controllers.
He had Victron, Renogy and a few brands I hadn't heard of before.
He stated unequivocally that you CAN run two controllers into one battery bank. So long as you do not exceed the max charge amperage for the batteries by doing so.
He seems to know a lot more about solar stuff than I do, so I bow to his superior wisdom.

 

[CosmickGold]

Web pages such as this one on panels and this one on chargers helped me understand the following really well so I can now explain it to you:

First of all, I suggest you return both of your PWM charge controllers to Renogy in exchange for a single MPPT controller. MPPT costs more, but there are two good reasons for making this switch:

(1) MPPT controllers are 30% more efficient, meaning you'll get another 30% charge to your batteries from a given amount of sunlight.
(2) PWM controllers can not handle more than 20 volts, so they can't allow you to perform the improved wiring of your panels I've described below.

Solar panels can produce nearly 20 volts each in full sunlight, but the lower the light they receive the lower the voltage they produce. At the same time, a battery requires about 14 volts -- not 12 -- to be charging, or your battery will just sit there and not charge. This means the panels must be getting enough light to be running at a minimum of 70% capacity (14 volts) to be actually charging your battery.

On the other hand, an MPPT controller can handle up to 80 volts coming in from the solar panels. With your four panels wired in parallel, the output voltage will still be the same 20-volt max of one panel (not much of an advantage) which is all your PWM controllers can handle. But with an MPPT controller, you can hook the four panels in series to produce up to 80 volts! (20+20+20+20) This is great, because if it's cloudy, early morning or evening when the sun is low, your solar panels only need enough light to be working at about 25% capacity to still be giving your controller 20 volts total so it can easily be giving your battery the charge it needs. Add this to the 30% added efficiency of an MPPT controller, and you've really got it "made in the shade". (Pun intended.)

****

FYI: Hooking four solar panels in parallel is like setting four building blocks side by side; the four together will still only be as tall as a single block (20V). But hooking your four solar panels together in series is like stacking those same four building blocks on top of one another, giving them four times the height of a single block (80V).

FYI: Some web pages state that wiring panels in series will cause any panel receiving insufficient light to block the other panels from getting their full voltage through to the charger. This is true of some types of panels but not of panels made by Renogy; for Renogy installs diodes inside their panels to send the electricity around any panel -- or section of a panel -- that is not doing its job. Therefore, no such problem exists with Renogy solar panels.

 

[frater secessus]

Web pages such as this one on panels and this one on chargers helped me understand the following really well so I can now explain it to you:

<takes sip of coffee>

First of all, I suggest you return both of your PWM charge controllers to Renogy in exchange for a single MPPT controller. MPPT costs more, but there are two good reasons for making this switch:

Combining panels with disparate specs on the same controller typically results in lower power harvest than with separate controllers.

(1) MPPT controllers are 30% more efficient, meaning

They aren't. MPPT is negatively affected by inefficiencies that generally do not apply to PWM systems: buck conversion losses, cell temperature derating, wiring losses, etc.

Sometimes these inefficiencies stack up so much that, in edge cases, PWM can make more power than MPPT.

you'll get another 30% charge to your batteries from a given amount of sunlight.

You won't.

Average daily increase from MPPT is typically closer to 15%. The +30%-40% numbers are real, but only occur in circumstances when local panel/string Vmp is significantly higher than Vbatt (battery voltage) and the system can take advantage of it. Bulk stage, for example. In float or late absorption there may be no MPPT advantage at all.

Whether or not +15% is worth 2x-3x the price is a matter for the consumer. Horses for courses. (I use MPPT, PWM, and shunt controllers for different purposes).

(2) PWM controllers can not handle more than 20 volts,

They can.

The PWM controller will have an input voltage max just like MPPT. You can charge a 48v battery from a 48v solar config with PWM for example.

Solar panels can produce nearly 20 volts each in full sunlight,

Panel voltage can be much higher than that. Mine are running at 30.8v right now.

but the lower the light they receive the lower the voltage they produce.

Doesn't work that way. Voltage is quite stable above 20% insolation (like shortly after daybreak). Current will vary based on conditions.

At the same time, a battery requires about 14 volts -- not 12 -- to be charging, or your battery will just sit there and not charge.

Depends on battery chemistry and number of cells.

On the other hand, an MPPT controller can handle up to 80 volts coming in from the solar panels.

? This is a controller spec. Mine goes to 150v, and some go higher. Some are as low as 23v.

With your four panels wired in parallel, the output voltage will still be the same 20-volt max of one panel (not much of an advantage) which is all your PWM controllers can handle.

When I blew a controller in the summer I put my 24v panels in parallel on a spare PWM to charge my 12v bank. The PWM ran the panels at Vbatt, which is effectively how PWM works.

But with an MPPT controller, you can hook the four panels in series to produce up to 80 volts! (20+20+20+20) This is great, because if it's cloudy, early morning or evening when the sun is low, your solar panels only need enough light to be working at about 25% capacity to still be giving your controller 20 volts total so it can easily be giving your battery the charge it needs.

Cloudy weather generally does not alter the voltage of solar panels.* In early morning or late evening insolation can drop below ~20% and voltage can crash, but so little power is available at those times that it is not a compelling argument for series arrangements. (I use series but not for that purpose).

MPPT is typically most efficient (lowest buck losses) when panel voltage (Vpanel) is about 2x battery voltage. Check your MPPT manuals for the relevant efficiency curves.

FYI: Some web pages state that wiring panels in series will cause any panel receiving insufficient light to block the other panels from getting their full voltage through to the charger. This is true of some types of panels but not of panels made by Renogy; for Renogy installs diodes inside their panels to send the electricity around any panel -- or section of a panel -- that is not doing its job. Therefore, no such problem exists with Renogy solar panels.

Section of a panel is correct; that is the bypass diode's job. Around any panel is incorrect, but it can be accomplished with external bypasses. Some controllers will also reduce overall string voltage to deal with shaded panels but that is a different (and more complex) topic.

---

For anyone who's read this far, I have attempted a rubric for choosing between MPPT and PWM in this RVwiki article.

* it may affect the voltage at which MPPT runs the panels

 

[CosmickGold]

Seems you really know your stuff, Frater. I just searched through some websites to get their info to share here, with no proof about who's correct. The person who explains these things should instead be someone with first-hand experience on each issue, which appears to be you.

On my van, I started out with two 100w Renogy panels and a PWM controller which I didn't like. Soon I got two more 100w panels and an MPPT controller and have been a happy camper ever since, never again running out of power. But that's the limit of my hands-on experience.

Thanks for the corrections on the other stuff where I lack any first-hand experience.