Best Vmp for use with SolarBoost 2000E

Re: Best Vmp for use with SolarBoost 2000E

Tony is correct. And your AEE contact is correct--but possibly wrong too...

The Solar Charge converter will simply maximize the solar panel output following the formula Pmax=Vmp*Imp and the battery output will be Pbatt=Vbatt*Ibatt (less some 5-10% or so power loss)--so absolute voltage and current do matter.

However, Solar panel voltage must be in a range the charge controller can use... Obviously, too high, the controller is ruined. Too low, the charge controller cannot pass solar panel energy to the battery.

Basically, the solar panel voltage must be greater than Vbatt-charging+controller drop.

Vbatt-charging would be ~14.5 volts during normal charging, and controller voltage drop is around 1-2 volts (plus, you will have some voltage drop in the wiring too).

Also, for flooded cell lead acid batteries, you will need to charge them at a higher voltage every few weeks or so--called "equalization"... That voltage can be around 15-15.5 volts.

So, just from a conservative point of few, the solar charge controller (which can only drop voltage, not increase it):

Vmp >= 15.5v + 2v = 17.5 volts to equalize
Vmp >= 14.5v + 2v = 16.5 volts for normal charging

And then you get into the ugly details.

Batteries require higher voltage to charge if they are cold, and lower voltages if they are warm (~77F is "spec. temp.").

And, solar panel Vmp (and Voc--open circuit) vary with temperature. When the panels are cold, they output higher votlages, and when the panels are hot, they output lower voltage.

So, if you have cold batteries, on a hot, sunny, windless day, your Vmp of the panels may not be able to output enough voltage to poroperly charge/equalize your batteries.

If the Vmp is correct for your panels, then the Vmp=16.7volts is getting very close to putting you in the gray zone where you have the "energy" of the panel, but not enough voltage to push current into the batteries. Remember solar panels get hot under full sun (black object under glass). And even on a 80F day, it is possible for your 16.7v panel to drop down to ~14 volts Vmp if mounted flat to the roof (poor cooling) on a windless day.

So, your questions to ask:

• What is the Vdrop requirement of the BlueSky controller
• What is Vmp for your panel
• What is the Voltage Temp Coeff - Vtoc (something like -0.0824 V/°C)
• What are the Vbatt-charge voltages for your battery bank
• What are the temperatures of your batteries
• What are the temperature of your solar installation
• Will there be airflow around the panels (i.e., tilted up / raised up from roof for better ventilation)

-Bill

By the way, Vmp is a "fuzzy voltage"--the panel will output higher voltage, but at less current--so the system may still charge--it just won't do it with Imp*Vmp--V will be a bit higher, and Imp will be much lower--so P=V*I into the battery bank will be lower too.

Re: Best Vmp for use with SolarBoost 2000E

You are welcome "K".

Regarding wiring everything together... Generally, think of the battery as the "center" of the system, and everything else is "hung" off of it.

So the "+" point and the "-" common connection points should have a striaght, large wire (or copper bus bar), short and well protected against metal to metal contacts (short circuit possibilities) to the battery as possible. If there is voltage drop anywhere, it costs you power and makes it more difficult to fully and quickly charge the battery.

You may have a large fuse from the battery to the "+" bus bar/common connection point (for safety). And, in any case, you should have 1 fuse or circuit breaker for each branch that goes off of your common "+" point. This is to protect your wiring from melting if there is a short anywhere else in the positive run from the fuse to the AC charger, Solar Charger, interior lights, fan, radio, etc...

There should be no fuses in the negative path.

The battery can supply amazing amounts of current and you need the fuses/breakers to prevent cooking the "smaller" wires that go throughout your trailer.

Typically, the best wiring for your chargers is to use the recommended wiring practices to the common "+" and "-" connections for the battery.

I would not recommend, for example, using the same wiring from the AC Charger and the Solar Charger to the battery--the higher current from both chargers running will increase the voltage drop along the wiring--raising the "apparent" battery voltage (Vbatt+Vwire-drop) and fool the controllers into thinking the battery is charged higher than it really is.

Also, if your controllers support it, get a remote battery temperature sensor. This can get you another 5-10% more charge in your battery...

It may not sound like much, but typically (for example). You charge your batter to 90% (controller error), discharge another 10% per day in normal usage, and in 1.5 days you are at 75% state of charge--if you discharge below this point for more than a few hours (usually less than one day), the sulfates will begin to harden in the flooded cell lead acid battery and cause its early life failure (or you have to run the generator every day or so to bring the battery back up).

If you charge the battery to 100%, then you now have 2.5 days of useful power before you need to run the genset (for bad weather, parked under trees).

Undercharging is probably the #1 killing of batteries (#2 is probably overcharging). We all go through a set or two of batteries before we get the hang of it.

Read through our host's website/store (NAWS)... They have posted many little FAQs around in the major sections (batteries, inverters, charge controllers, etc.) that do a very good job of answering many of these questions in detail.

-Bill

And to add to what "hillbilly" said... Your charge controller will only output Pmax when the battery is ~less than 90-80% full). Once the battery is over 80-90% full, the controller cuts back on the charging current. Another reason that having an accurate battery temperature sensor helps ensure a quick charge and good use of your $$$ you paid for your $olar panel$ and batterie$.

Re: Best Vmp for use with SolarBoost 2000E

Are you asking about (from the installation/user manual):

The primary purpose of the load control function is to
disconnect system loads when the battery has discharged
to a low state of charge and reconnect system loads when
the battery is sufficiently recharged. System loads may be
lights, pumps, motors, DC appliances, and other electronic
devices. The total current draw of all loads must not exceed
the SS-MPPT 15 Amp maximum load rating.

Basically, if the battery goes dead, the LVD (low voltage disconnect) turns off any attached loads until the solar panels have recharged the battery bank somewhat... Note that the LVD has a 15 amp maximum current limit--so most people don't even use it. And don't attach any heavy loads (like an inverter). They will just blow the internal switch.

The LVD does not divert any extra power or anything fancy. It just turns off the loads before they can run the battery dead. It would be the same if you just turn off your loads when the battery is being over discharged. LVD's are not very accurate and generally are a last resort to prevent running a battery dead.

I am not sure what you are saying about your fuse block... Each positive wire leaving the battery bus/common point should have its own fuse that protects the wire in case of shorts (or one fuse protecting several wires if the loads are small enough).

And yes, you can run your entire system without attaching to the LVD. Or, you can attach a few small loads (lighting and such through fuse block if needed) to the LVD if you want.

-Bill

Re: Best Vmp for use with SolarBoost 2000E

I have some comments... Don't take any of them wrong--because I may not know what your final intent is.

1. If you are worried about heat, place the controller low in the closet so that the heat rises. Right now, you have the controller sitting in the hottest point of the "room". You may want to cut vents in the door for better ventilation. 5% power loss of 200 watts is 10 watts of power--not a huge amount (like two 120 vac night lights). But, things do last longer if kept cool. I would also lower the controller as this keeps your battery to bus bar (the heavy black wires) short too. Not a problem in this installation--but short & heavy controller to battery connections can only help in the long term.
2. You might want to put some sort of "shield" over the installation if there will be things put in the closet to prevent shorts, blocking of air flow, and melting of items that touch hot surfaces (possibly made hot by shorts or blocked air flow).
3. Where is your main battery fuse? I see what appear to be bus bars near the controller--but no fusing. assuming your bus bars are the "common connection point" all your wires leading off of them should have a fuse each (your fuse block connected to the positive bus bar would be a good solution).
4. The fan is a constant load; with solar, reducing power use to the bare minimum will be your mantra--It would be better to not have it at all (or at least use a switch/thermostat to turn it on only when needed).
5. The fuse block connected to the LVD connection is fine for "small" loads--but having it connected to the main + bus bar for the major loads (or a second fuse block) is best.
6. You have a white "ground wire" from the LVD ground to the small ground bus. I would not do this... You may end up with a "ground loop" through the controller (basically two ground wires in parallel). It is not needed, and can cause damage when loads are connected. Either connect all of your load returns to the big brass - bus bar, or connect the LVD loads to the LVD ground--not both.
7. You appear to have two - bus bars in the picture. One really nice big brass one. And a second smaller one with white wires attached. Connect your "small ground bus" wire (goes down in picture?) directly to the big brass - ground bus. Also, make sure that all of the currents from your ground returns that go to the "small ground bus" do not exceed the wire ampacity from the "small ground bus" to "big brass ground bus" connection. (currently your wire appears to be ~14 awg--plan on about 15-20 amp maximum current for safety. Remember voltage drop--so keep small gauge wires short and with low current).
8. You have no external temperature sensor connected. The external battery sensor is just about mandatory for this charge controller (internal sensor usually undercharges the battery). Especially important as the controller is mounted in a warm closet--makes the undercharging worse.

Again, just what I see/understand at this point. I know you are not done yet.

-Bill