Charging current and other newbie stupid questions

[wa1gon]

OP, you bought the wrong stuff but it would help to know your loads so we could help you configure your current equipment as best it can be. Also need distance from panels to CC. The PWM CC is reducing your panel to half but if you can reconfigure your batteries to 24V you can get closer to the rated panel output.

Yes, it is now clear that I should have got a MPPT CC, I am going to return 2 of the 3 C40s and get MPPT.

I am trying to keep my daily power budget under 5400 watt/hrs per day, which will be 50% of my batteries.

Distance from panels to batteries is an unknown at this point. Which is why I wanted the option for high voltage.

I have been seeing some lower cost MPPT chargers on E-Bay. Does anyone know anything about them?

thanks
-darryl DE WA1GON

[SunEagle]

Yes, it is now clear that I should have got a MPPT CC, I am going to return 2 of the 3 C40s and get MPPT.

I am trying to keep my daily power budget under 5400 watt/hrs per day, which will be 50% of my batteries.

Distance from panels to batteries is an unknown at this point. Which is why I wanted the option for high voltage.

I have been seeing some lower cost MPPT chargers on E-Bay. Does anyone know anything about them?

thanks
-darryl DE WA1GON

Buying anything off eBay especially items that cost much less then a known quality item can be a crap shoot. More than likely the sellers claims are false but you won't know until you get the item and then it may be too late.

Unless you know the seller I would be very careful of trying to save a few bucks only to find out the item is junk.

Check out the link I posted earlier to the Solartown Store. You will find quality items that can be trusted there.

[thastinger]

Yes, it is now clear that I should have got a MPPT CC, I am going to return 2 of the 3 C40s and get MPPT.

I am trying to keep my daily power budget under 5400 watt/hrs per day, which will be 50% of my batteries.

Distance from panels to batteries is an unknown at this point. Which is why I wanted the option for high voltage.

I have been seeing some lower cost MPPT chargers on E-Bay. Does anyone know anything about them?

thanks
-darryl DE WA1GON

There are a few folks here who have bought those CC to test, IIRC they were all actually PWMs with the possible exception of one and the jury was hung on that one as to what it was.

[wa1gon]

Thank you all for the advice. It has been very helpful

You guys have been been great! Thank you!

I have requested an RMA on 2 of the 3 C40s CC that I haven't opened. I will keep the 3rd one as a load controller. I would have keep them all as load controllers, but didn't have the money right now.

I have ordered a MorningStar TriStar TS-MPPT-60-MPPT may reasons:

1. Trusted name brand
2. MPPT
3. Ethernet connection (this will save me money on monitoring)

My plan is to purchase 2 more of these controller and then add more panels. Batteries will be the last thing I buy

Someone suggested changing to a 24v system. I decided not to do that because all my devices were 12v and I didn't think it was a good idea to try to tap 12v from a 24v bank. Is there a better way?

Another thing I am trying to rap my head around is when the PV a producing power and there is a load, where does the power mainly come from? PV or the batteries? Not sure if it really matters, just wondering.

thanks again
Darryl DE WA1GON

[Mike90250]

....

Another thing I am trying to rap my head around is when the PV a producing power and there is a load, where does the power mainly come from? PV or the batteries? Not sure if it really matters, just wondering.

thanks again
Darryl DE WA1GON

The power comes first from the sun, if there is enough. If not, the batteries make up the difference.

Beware, some loads won't like the 14.5V that may be present in ABSORB or 15.5V in EQUALIZE.

[wa1gon]

Battery Voltage

Here is another question that I don't understand all I know.

I have a volt meter connect across my load leads.

Without a load the meter reads about 12.67 volts.

However if I put a load of say 10A(120 watts) my voltage drops to about 11.8V.
I am using 10 gauge wire with less than 20 ft to the battery.

What is causing this voltage drop?

I assume this is normal. What happens if the load is 20 or 40 amps?

Thanks
-darryl DE WA1GON

[Sunking]

If you measure the voltage on the battery post and it sags means your battery is toast. If battery voltage holds up, but sags at the utilization equipment power input means you have a wiring or connection issue.

[greenHouse]

Not a good idea to have more than one charger unless they are exactly alike and talk to each other otherwise they will fight each other to charge the batteries.

Better to use one charge controller sized appropriately for your batteries.

A quality MPPT type charger is the Morningstar but our Sponsor sells all types. Check out this link.

http://www.solartown.com/store/catal...e-controllers/

Charge controllers talk to each other through the battery voltage, they don't need to talk to each other any other way.

What =can= mess things up is having the charge controllers set up differently. But the "fighting" people worry about is no big deal -- the batteries will only accept however much current they'll accept, and that's that. If you're concerned, set one charge controller slightly lower than the other and the second charge controller will finish the charge off in absorption.

[inetdog]

Charge controllers talk to each other through the battery voltage, they don't need to talk to each other any other way.

What =can= mess things up is having the charge controllers set up differently. But the "fighting" people worry about is no big deal -- the batteries will only accept however much current they'll accept, and that's that. If you're concerned, set one charge controller slightly lower than the other and the second charge controller will finish the charge off in absorption.

What you say is correct for the constant voltage stages (Absorb and Float) but not for Bulk, which is a constant current stage.
The bad thing that can happen if you have too much total panel power is that both CCs in parallel may push too much current to the battery when they are both in Bulk stage and do not know about each other.

[Sunking]

both CCs in parallel may push too much current to the battery when they are both in Bulk stage and do not know about each other.

Maybe, maybe not. This is where the max C/8 charge current comes from. Go above C/8 on FLA batteries and the battery internal resistance will cause a false set point to be reached to quickly before you get to 80% SOC and go to absorb prematurely which is not a real problem because in Abosrd you are in a CV stage and the current will back off to stay at ABSORB voltage.

This is why I say Set Bulk = to Absord as bulk is really useless stage in solar applications. Set it to BULK and the controller will be in CURRENT LIMIT or CC stage until Absord set point is reached then goes to CV Current Taper. Float and Aborb are really the same thing except Flot is just a lower voltage.

Get out in the real world of professionals like TELCO and DATA and they only use FLOAT and once in a rare Blue Moon will EQ on FLA, but generally EQ is never used.

[inetdog]

Get out in the real world of professionals like TELCO and DATA and they only use FLOAT and once in a rare Blue Moon will EQ on FLA, but generally EQ is never used.

Which is also most often the world where batteries are not cycled daily, but just sit there waiting to be needed.
There is also the real world of fork lift operators who need to recharge the batteries after every shift, and use yet a different charging profile (and battery construction for that matter.)

[inetdog]

This is where the max C/8 charge current comes from. Go above C/8 on FLA batteries and the battery internal resistance will cause a false set point to be reached to quickly before you get to 80% SOC and go to absorb prematurely which is not a real problem because in Abosrd you are in a CV stage and the current will back off to stay at ABSORB voltage.

If you go to, for example, C/4 or higher, will that be doing any damage to the batteries, starting from a low SOC so that they spend some time at that rate? Or will kicking into absorb too soon be the only effect?
I can imagine that for sealed cells you would run the risk of excessive gassing and damage, yes? (In this case the limiting rate would be higher, and determined by temperature and recombination rate/pressure, but the same question applies to what happens if you go above that rate during Bulk.)

[greenHouse]

What you say is correct for the constant voltage stages (Absorb and Float) but not for Bulk, which is a constant current stage.
The bad thing that can happen if you have too much total panel power is that both CCs in parallel may push too much current to the battery when they are both in Bulk stage and do not know about each other.

That's a design problem, not a methodology problem. The peak charging rate, for all charge controllers in total, shouldn't exceed the manufacturer's recommended maximum charge rate for the batteries.

What drives owners to distraction is the misguided belief that if both charge controllers aren't putting out exactly the same power (pro rated for array size), something is horribly wrong. What is ignored is that the acceptance charge for a given temperature and state of charge is reasonably fixed. And from that, the time to complete absorb is fixed, assuming a constant temperature.

[inetdog]

That's a design problem, not a methodology problem. The peak charging rate, for all charge controllers in total, shouldn't exceed the manufacturer's recommended maximum charge rate for the batteries.

Absolutely right. Earlier in the thread it looked like one of the posters was in need of design advice.