Can two Midnite Solar Classic 150 be used in parallel?

Saipro

I'm referencing this 2012 thread: Can you use two separate MPPT charge-controllers http://forum.solar-electric.com/foru...=1437804891996

I'm helping a friend with his off-grid plans and he wants to use two (2) Midnite Classic 150 in parallel to charge a common bank. I've scoured the web and found instances of attempts on it but nothing regarding the practical application. Can anyone help with this information? Thanks

boB

Depends on what you mean by parallel. If you mean can you put two Classics on ONE battery bank, then yes, of course. But if you mean, can you put one large PV array into TWO Classic INPUTs, the answer is no. You can parallel the battery outputs but not the PV inputs of two Classics. Each Classic must have its own PV array input.

Saipro

Yes, I meant putting two classics onto one battery bank. Now, read somewhere (speculative) about one CC sensing current in such a way that it recognizes the current in both the bank and that coming from the other CC as being bank current hence being unable to give optimal (or giving sub-optimal) current output. Does this mandate the networking of the Classics?

The real life application is this:
The entire is meant to provide inline backup for a hotel's lighting. The DC side primarily consists of
- Trojan IND17-6V 925Ah x 8 for a bank at 48V with 925Ah capacity
- 240W Joy Solar JYSP-240 PV panels x 40 in 2 arrays of 20 panels (4800W) to feed one CC each
- Midnite Classic 150 CC x 2

The whole point is to at least hit the 13% charge current once a week during the monsoon months when the skies are overcast most of the time with 2 - 3 hour lucky breaks. What do I need to do?

westbranch

you need more info, such as to the daily depth of discharge and days of autonomy you have planned for, backup generator , inverter and the peak loads to be handled...
hth

Saipro

I have those other details worked out, hence the sizing of the banks and the number of panels required to charge back fully in one day as well as supply a liitle extra punch during the clear sky harmattan season. It's the configuring of the Classics that seems to be my Achille's heel. Can I just hook them up in parallel to feed the same back straight out of the box or must I network them to each other?

BB.

With MPPT controllers, you can connect both to a single battery bank (I recommend that each controller have its own wire run--Don't "daisy chain" the controllers--Battery to controller A to controller .

Each MPPT controller should have its own solar array input (you cannot share one solar array with two or more MPPT type charge controllers).

You don't have to network them together--What will happen is that the transition from Bulk to Absorb to Float will not be "identical"--One will change modes before the other. This is not a problem, but minor voltage/timing variations will cause this to happen.

-Bill

Saipro

Thanks Bill. Wasn't willing to found out raw if it wouldn't work. The cost of the equipment/investment could bring a man to his knees should things go south.

Vic

Saipro,

The MidNite Classics can be "Networked", so that they can share the same Charge State. This networking is via a Phone Cable -- standard four-conductor. So each Classic should be located close to the other.

This interconnection and the communication function between the Classics is called ' Follow Me '. There is no specific communication or process that will cause the two Classics to share the charging power delivered by each CC. But having the two CCs share the Charge State is a huge advantage.

One fairly common frustration with more than one CC that do not have the Follow Me capability, is that one will decide that it is time to go to Float, stranding the other CC/s in Absorb. Without the power contribution of the CC that just went to Float, the stranded CC often cannot maintain the set Absorption voltage, and it reverts to Bulk for the rest of the day. This is not a real big deal, but it can result in increased water consumption, and perhaps can add a certain amount of additional Plate Erosion, etc, IMO.

FWIW, Vic

Ethan Brush

Vic wrote: »

Saipro,

The MidNite Classics can be "Networked", so that they can share the same Charge State. This networking is via a Phone Cable -- standard four-conductor. So each Classic should be located close to the other.

This interconnection and the communication function between the Classics is called ' Follow Me '. There is no specific communication or process that will cause the two Classics to share the charging power delivered by each CC. But having the two CCs share the Charge State is a huge advantage.

One fairly common frustration with more than one CC that do not have the Follow Me capability, is that one will decide that it is time to go to Float, stranding the other CC/s in Absorb. Without the power contribution of the CC that just went to Float, the stranded CC often cannot maintain the set Absorption voltage, and it reverts to Bulk for the rest of the day. This is not a real big deal, but it can result in increased water consumption, and perhaps can add a certain amount of additional Plate Erosion, etc, IMO.

FWIW, Vic

It is nice that the classics have the follow me feature. I would think that should be a standard feature from all manufacturers - seems like a no brainer to me..... Here is a white paper from Morningstar discussing paralleling multiple controllers (their controllers do not communicate with each other).

http://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/

Saipro

Vic wrote: »

Saipro,

The MidNite Classics can be "Networked", so that they can share the same Charge State. This networking is via a Phone Cable -- standard four-conductor. So each Classic should be located close to the other.

This interconnection and the communication function between the Classics is called ' Follow Me '. There is no specific communication or process that will cause the two Classics to share the charging power delivered by each CC. But having the two CCs share the Charge State is a huge advantage.

One fairly common frustration with more than one CC that do not have the Follow Me capability, is that one will decide that it is time to go to Float, stranding the other CC/s in Absorb. Without the power contribution of the CC that just went to Float, the stranded CC often cannot maintain the set Absorption voltage, and it reverts to Bulk for the rest of the day. This is not a real big deal, but it can result in increased water consumption, and perhaps can add a certain amount of additional Plate Erosion, etc, IMO.

FWIW, Vic

Yeah, I saw the "follow-me" feature but didn't consider the significance until you mentioned it. It's true (theoretically) that one CC could be stranded in absorb/bulk (why didn't that ever occur to me?)

Unless I get other counter-ideas/counter-suggestions, I guess follow-me it is. Seems you understood my question better than even I

zoneblue

Follow me works good, but its not really the end of the world without it. Just calibrate both controllers voltage settings to within 0.1V (do need an adjustable controllers for this, but you need that anyway, right...). The differences will only kick in when the controllers start to throttle back later in the charge stages. During bulk both will work as hard as each other, sourcing current with the battery dictating the voltage of everything.

inetdog

zoneblue wrote: »

FDuring bulk both will work as hard as each other, sourcing current with the battery dictating the voltage of everything.

Which does bring up the potential problem of excess Bulk stage current into the battery bank unless the array power limits it sufficiently.

Saipro

inetdog wrote: »

Which does bring up the potential problem of excess Bulk stage current into the battery bank unless the array power limits it sufficiently.

Hmm. Pretty interesting stuff. My first post on this forum addressed the concern of oversizing an array to forestall the "sunless"/cloudy days, as they prove to be the Achille's heel of any PV system. I was reassured by emminent members that I had little to worry about. Indeed, they were proved right (though I eventually beefed up the bank size).

On my own setup which utilizes Trojan T105-RE batteries, I seem unable to force more than 13% of their rated capacaity in as charging current during bulk mode (unless discharged to about 40% in which case I get up to 17% for a brief run while things are settling down). I guess that's part of the "smart" battery design.

Photowhit

But does the battery dissipate the excess as heat?

inetdog

Photowhit wrote: »

But does the battery dissipate the excess as heat?

As long as you do not exceed the nominal Bulk voltage, the higher current will heat the battery somewhat, enough to potentially cause thermal runaway problems if the CC does not use a remote temp sensor.
And the charging efficiency will be lower since there will likely be excessive gassing.
But a good portion of the excess current above the C/8 rule of thumb limit for FLA will actually go to charging the battery faster. It will just be reducing the battery cycle life disproportionately in the process.

The behavior you notice is not part of smart battery design, it is just a result of the terminal voltage and internal resistance of battery as functions of the State Of Charge (SOC).