Awesome new MPPT controller with bluetooth control for $99 (1 Viewer)

[Rob Faucett]

Doesn't charging a battery "count" as load?

 

[george_tlc]

Doesn't charging a battery "count" as load?"

Yes, of course, but the mppt unit will only attempt to draw as much as it can to provide the charging profile that has been set and then only up to a nominal maximum of 15A output. It won't even output 15A if the panels can't provide the necessary input voltage (remember this unit will attempt to perform mppt).

No different than if you had a mains charger connected to the battery and to your 110VAC input. After all, with your thinking the power station your mains charger is connected to could provide gigawatts... It's not like the mains charger then explodes because the power grid attempts to "send" gigawatts to the charger...

That's was what my statement tried to elude regarding a solar panel not outputting any power if the load doesn't pull any. In this case the load to the solar panel is the mppt controller. So, it is the mppt controller that decides how much power to try to draw, not the solar panel 'sending' power. If the battery is quite discharged then it's possible that the mppt controller will output say 13V at 15A (13V x 15A = 195W) even if the solar panel was capable of 'providing' 1000W... The extra panel capability is just not drawn upon.

cheers,
george.

 

[Rob Faucett]

Gotcha. Great explanation. Thanks for taking time. Much appreciated.

 

[Suprasoup]

Thanks George!! - So I can't "blow it up" by sending to much power from the panels into the MPPT?

Be careful here. You can absolutely “blow up” ( I prefer let out the magic smoke) your charge controller if you over panel it.

There are two numbers to look at on your charge controller. 75/15. The 75 refers to the maximum open circuit voltage the panels can input into the charge controller before you fry it. The 15 refers to the current it can output.

Power =volts x amps.

So this controller can output 12v x 15a = 180watts max at 12v nominal. At 24v nominal it can output 360watts.

Since most of you are using 100w panels or some derivative lets use the 100w renogy panel as an example.

Voc (voltage open circuit) = 22.5v.
Isc (current short circuit) = 5.75a
Maximum series fuse =15a

So wire 1 panel to the charge controller and your good. How about 2? Decision do you wire them in series or in parallel? Wire in series and the voltage of the panels goes up and current stays the same. Wire in parallel and the current goes up.

Series
2 x 22.5v = 45v. ( charge controller can handle that.) how about 3? 3 x 22.5v = 67.5v. Cutting it close there. Heck since they measure Voc at STC conditions one cold winter morning and you’ll see your charge controller smoke because Voc rises with a decrease in temp from STC conditions. So stick to wiring 2 panels in series for this controller or roll the dice with 3 and hope it doesn’t get cold. Good rule of thumb take your Voc and multiply 1.25. That will keep you safe.
4 x 22.5v = 90v. Yup you just toasted your charge controller. No ifs ands or buts.

Parallel.
1 x 5.75a = 5.75a. Below the maximum series fuse limit. No fuse necessary. Short circuit the panel and all you get is a little heating of the wires. You can do this all day.
2 x 5.75a= 11.5a. So you are below fuse current of the solar panel. No fuses necessary. The solar panel wires (12awg in this case) can handle it.
3 x 5.75a =17.25a. You are above the fuse current of the solar panel. Better have a fuse on EACH of the solar panels. You know all those little copper traces that connect the individual cells? Well up in smoke.
4 x 5.75a = 23a. You are above the fuse current rating of the panel AND the current rating of the 12awg wire. So you burn down your panel as well as vaporize your wires. Hope you got a fire extinguisher cause you are gauranteed a fire.
Stick to 2 parallel strings of solar panels.


So....Don’t over panel. There are real consequences. And I haven’t even gone into what happens when you over current a charge controller.

I’ll go into that on another post.

BTW the math works for every solar panel whether grid tied or 12v. Just look up the spec sheets.

 

[Rob Faucett]

So....Don’t over panel. There are real consequences. And I haven’t even gone into what happens when you over current a charge controller.

I was concerned about "over paneling" by about %15. So no problem. Thanks for taking the time.

 

[george_tlc]

Parallel.
1 x 5.75a = 5.75a. Below the maximum series fuse limit. No fuse necessary. Short circuit the panel and all you get is a little heating of the wires. You can do this all day.
2 x 5.75a= 11.5a. So you are below fuse current of the solar panel. No fuses necessary. The solar panel wires (12awg in this case) can handle it.
3 x 5.75a =17.25a. You are above the fuse current of the solar panel. Better have a fuse on EACH of the solar panels. You know all those little copper traces that connect the individual cells? Well up in smoke.
4 x 5.75a = 23a. You are above the fuse current rating of the panel AND the current rating of the 12awg wire. So you burn down your panel as well as vaporize your wires. Hope you got a fire extinguisher cause you are gauranteed a fire.
Stick to 2 parallel strings of solar panels.

No idea what you even mean here. 23A is too much for 12AWG - based on what facts??

Why would the solar panel traces burn up with 4 panels in parallel?

Please elucidate with some engineering facts - love to learn from you.

The only thing I agree is you need to keep the input voltage (if you go series on the panels) to below the maximum input voltage rating of the controller. Please note that for this discussion the controller is an MPPT unit with DC to DC voltage conversion AND does monitor the output current and therefore will limit it to a safe level to protect its DC to DC output electronics.

cheers,
george.

 

[Suprasoup]

No idea what you even mean here. 23A is too much for 12AWG - based on what facts??

Why would the solar panel traces burn up with 4 panels in parallel?

Please elucidate with some engineering facts - love to learn from you.

The only thing I agree is you need to keep the input voltage (if you go series on the panels) to below the maximum input voltage rating of the controller. Please note that for this discussion the controller is an MPPT unit with DC to DC voltage conversion AND does monitor the output current and therefore will limit it to a safe level to protect its DC to DC output electronics.

cheers,
george.

Going by NEC Section 310.16 for wiring size. Since most of us arent using 90 degree C rated insulated 12awg wire I used the lower #'s for 12awg. in most cases 12awg wire can handle 23a easily but your terminations usually wont. Heating at the terminals causes long term damage and is more likely to short and start a fire. My use of the word "Vaporize" was overly strong.
Section 240.4 D deals with smaller wire sizes and their over current protection. In this case they limit it to 15a. Smaller wire size tend to behave differently when tripping circuit breakers or fuses so a lower rating is used to ensure that they trip reliably.

Second question is a good one. PV panels are generally considered current sources. So when the sun hits it it produces current. When a panel is short circuited it acts as a load and dissipates power through the panel as heat. Now the panels can only dissipate so much power before failing, as defined by UL 1703 testing. That's where the maximum series fuse rating comes from. Exceed that and the panel can overheat, smoke and catch fire.

NEC over current protection for a continous load (which a PV panel falls under ) is 1.25x Isc. PV panels can produce greater than their Isc under certain condition hence the multiplier. Typically how much irradiance. Temperature plays a small roll. So in the case of the Renogy 100w panel the overcurrent protection device (OCPD) would be 1.25 x 5.75a = 7.18a. As this # is lower than the Maximum series fuse rating no OCPD is needed. In a 2 parallel strings system if one panel were to be damaged (hail, short circuit) then the second parallel panel would dump it's current of 7.18a into the the damaged panel as that panel now acts like a load. Again the current is still less than the maximum series fuse rating. Even if you were to short circuit both panels together you would still fall below the fuse rating (2 x 7.18a)
Now once you get into 3 parallel panels and above is where you can run into trouble. You've now exceeded the maximum series fuse rating.

 

[george_tlc]

For vehicle usage we use lugs to connect to 12awg (or thicker) that easily handle 23A. Standard connectors used in our applications are Anderson SB50 and there's no issue at all with 23A. Typical wiring is automotive with appropriate insulation. Not sure why you are fixated on 12awg anyway. Most of us are running 10AWG or 8AWG or thicker depending on current carrying and length of wiring. This kind of wiring has insulation that is well rated about 90C maximum. Though I doubt anyone would be running 20A+ and not size wiring appropriately.

NEC ratings are typically looking at wiring in conduits, home wiring etc. This is automotive where we aren't running solar wiring in large bundles and along the exhaust system or inside walls... Cables are typically just in a sleeve and with plenty of air around them.

Fuses/circuit breakers of course are a smart thing to use in any wiring, especially vehicle.

Anyhow, glad you're looking at absolute worst case scenarios. Panels (at least the kind we use) have diodes to protect against reverse voltage (primarly to prevent battery discharge back into the panels at night), so even if one panel had severe shorts it would make no difference to other panels that are connected in parallel - no appreciable current will flow into the damaged panel.

All pretty moot given the majority of us are using 100W or maybe 200W of panels. We aren't talking about a house system or tops of RV's covered in panels. We're also specifically talking about the mppt75/15 and having 300W or 400W of panels connected to it (lets have them parallel and nominal 20V VOC) will not cause issues with it since it will limit its maximum output to a nominal 15A. Of course connecting more panel capacity than the controller can output will just be a waste of capacity.

Solar panels aren't quite current sources, they have an 'interesting' VI curve and that's why an MPPT algorithm works well to extra maximum power as the panel output varies with temperature,clouds,shading etc.


cheers,
george.

 

[Suprasoup]

Agreed most users on this forum are probably not going exceed 100-200w though I thought I saw someone upstream referencing 3 100w panels.

12awg was the wire size on the renogy 100w panels I was using as an example.

Are you confusing bypass diodes for blocking diodes? All panels these days have bypass diodes to deal with shading issues. Blocking diodes are usually found in the charge controller. Case in point the renogy 100w panel has bypass diodes and no blocking diodes.

appreciate the banter. Always helps to flesh out the hows and the whys. Take what you will and scrap the rest.

 

[george_tlc]

^ No, solar panels in this style of product typically have series connected blocking diodes. I'm not confused Simple to verify.

The diode is usually found in the little terminal junction box on the back of the panel where you connect your wiring. Blocking diodes are not needed in a charge controller that has decent drive circuitry (e.g. mppt controllers of this class - they don't leak current back from the battery to the charge controller).

12awg is still more than sufficient for 300W of solar panels (30A is not an issue for panel to controller wiring in these low voltage applications). Though most of us would not want to suffer significant voltage drop and would therefore move to larger wiring diameter.

Some examples of information for wiring that is more in tune with vehicle wiring (low voltage) versus NEC stuff:

Marine Wire Size and Ampacity | West Marine

American Wire Gauge Chart and AWG Electrical Current Load Limits table with skin depth frequencies and wire breaking strength (note their maximum values are VERY conservative).

e.g. fusing current (10 second fuse time) for 12awg is nominally 235A...

cheers,
george.

Fix dumb typo...

 

[Vlex]

Just got my Victron 75/15 with Bluetooth and could use some advice on placement.
From what I understand it is best to mount it close to the battery. I'm now thinking of mounting the unit in front on the battery, inside the battery box of a FZJ80. Only concerns I can think of is the temperature under the hood and the fact that the unit isn't IP67 rated. But I think that the battery box would keep most of the water/elements away.
Any advice would be appreciated.

Picture grabbed from the internet, not my FZJ.

 

[george_tlc]

I'd mount it inside the vehicle, say up near the driver side firewall (above pedal area) and then run cables through the firewall. We're only talking 15A max so not like you need to run 1g wires etc... The small voltage drop won't make a significant difference to charging accuracy.

cheers,
george.

 

[Overland Tailor]

Agree with George and Keep it out of the engine bay. They are fairly robust units, but I doubt you could get any longevity keeping it in there... But some have them there so I guess well see.

Best,

John

 

[e9999]

Vlex, it seems that it would be problematic to mount it exposed to the elements. And it's not like it's never raining in the Netherlands (if you do indeed plan to use it there). I would look into whether it would be worthwhile to use a remote temperature sensor, though, if available for that model, given that the temperatures can indeed be quite high under the hood.

 

[Vlex]

Thanks guys!
I guess the unit goes inside the cab
Just took a peak at firewall/pedal area and found 2 free studs at the LH side of the CC-ECU. (anyone know what was mounted here?) Looks like perfect spot for the charge controller!
I'm thinking of putting an Anderson plug in the vents of the front-bumper for the solar panel connection, any arguments against this idea?

 

[LS1FJ40]

Just got my Victron 75/15 with Bluetooth and could use some advice on placement.
From what I understand it is best to mount it close to the battery. I'm now thinking of mounting the unit in front on the battery, inside the battery box of a FZJ80. Only concerns I can think of is the temperature under the hood and the fact that the unit isn't IP67 rated. But I think that the battery box would keep most of the water/elements away.
Any advice would be appreciated.

Picture grabbed from the internet, not my FZJ.

Thread hijack...Amsterdam is the best. I’ll hit you up next time we are there!

 

[MountNGoat]

Great thread, just ordered the Victron 75/15 with built in BT and a 160W Renogy flexible panel. Already have a Renogy 100W suitcase, looking forward to getting this all set up.

 

[Semi Hex]

If you like to dabble with the way you set your gear up, you’ll really like the blue tooth!

 

[Cruiserdrew]

And you can link your two panels in parallel if desired. I've done it and it works no problem. It's just hard to use that much power even with 2 fridges.

 

[spressomon]

Call me a skeptic but...21% efficiency from a bendable/foldable? Curious to see how it performs and how long it lasts.