12v battery/ 12./24v MPPT ~ 24v PV Panel

[Old___Slow]

This question troubles the Old and Slow mind. I have a 24v/120w Cynergy PV panel. I would like to use it for duel purpose. For my 24v e/scooter and my 12v RV, not at the same time. The MPPT states (15a 12v/24v), hook battery first, then panel/then load. What will happen with use for the 12v Is it mix and match? Just a novice. Like one fine fellow said, who am I, where am I and why am I here?



Floyd

[BFL13]

This is the LandStar manual for questions on equalizing etc.
I have the 20amper. Little more price, twice the amps in case you go crazy and get more wattage of panels (nobody ever does that---)

http://www.pvsolarchina.com/wp-content/uploads/2012/09/User-Manual-of-LS1024-LS1524-LS2024-Solar-Con...

I have two of these 20ampers in parallel on the one battery bank and they operate just as one 40amper would for the charging profile going to Absorption and then to Float just as shown in the manual. No issues.

Yes, as I have posted in the past, these manuals seem to have been written by the same guy who writes the Morningstar manuals. Same drawings too. Can't say who is copying whom, or if MS is made by the same factory.

You MPPT guys getting into all this is very useful in learning about the various aspects. Seems to be quite a few aspects to juggle.

Load terminals. I guess that is for timed things like somebody said before. Actual loads are off the battery anyway and the solar just tops up the battery while the load is running, so why bother having a "diversion" when there is extra solar such as in the afternoon? Can't see any difference. If the panels would do 15 amps on a low battery but can only do 5 on the near full battery, you can run 10amps of load "for free" with no effect on the battery.

[pianotuna]

Hi KJINTF,

The Blue Sky 3024 is not what I'd call "cheap" and works fairly well. It does have "load" terminals and in the latest iteration can do a diversion load of 20 amps. I'd find that a useful feature.

Interestingly enough the Morningstar MPPT units don't do diversion loading--so that load feature perks my interest. I've maxed out my 3024 and will either have to buy a "slave" or have another independent controller when I upgrade the solar watts.

KJINTF wrote:
BLF

My first reaction would have to be the old adage "You get What You Pay for"
They copied / pasted the MS manual in many places.........
Looks as if they tossed in several useless features to make it look good. An example the load function which is typically only seen on low cost low power units

[red31]

BFL13

Do you know the logic for the LS1024 as to when it may equalize? MS claims once ever 28 days and epsolar manuals speak of when it detects overly discharge batt?
I'm interested in the waterproof LS1024RP

The 4210 has various efficiency curves in the back of the manual that shows a drop as the panel wattage increases and shifts as for 17v, 34v, and 68v

http://www.epsolarpv.com/en/uploads/news/201304/1366686104517198.pdf

[pianotuna]

Hi BFL13,

volts x amps = watts

380 watts max @ 12 volt out for the 30 amp
480 watts max @ 12 volt out for the 40 amp

Input voltage is independent of power out (so long as it is below 30 and 40, respectively) and only indicates a limitation of the controller's input parameters.

You could feed the 30 amp 150 volts @ 2.4 amps; or 100 volts at 3.8 amps. The wattage going into the controller remains the same in both cases.

The higher the input voltage the more of the energy will be wasted as heat inside the controller--so it still behooves one to use lower voltages unless you wish to save on the cost of #4 wire to the controller from the roof.

BFL13 wrote:
Doesn't that mean the 30 amper can have more total Voc and so more panels, but they have to be smaller to not go over the watts limit?
Seems backwards to me.

[KJINTF]

BLF

My first reaction would have to be the old adage "You get What You Pay for"
They copied / pasted the MS manual in many places.........
Looks as if they tossed in several useless features to make it look good. An example the load function which is typically only seen on low cost low power units

A few specifics
1 – Very limited configuration possibilities. That little numerical display would drive me nuts. The battery charge parameters are a bit limited
2 – External communications limited to none available. No way to interface a computer or anything else to remotely view status, system information, etc..
3 – No voltage sense line - not a big deal in many installs but for me a requirement when above about 25 amp capability
5 – No mention of meeting any World-wide electrical or safety standards. Could be fire and safety issues and or insurance issues your RV
6 – Limited built in fault prevention and alarms
7 – No battery EQ capability
8 – MPPT Tracking – unknown but looks better than some of the Blue Sky offerings with their "joke" user adjustable pots

That said for the price it might be worth taking a closer look at it. Some of the missing functionality might not impact the typical set and forget installation.

I would love to get my hands on one to play with it

[BFL13]

They say the 4210 has "Several seconds tracking speed" and claim this is "rapid tracking" for various temperatures.

[HiTech]

What is hard to get is the efficiency curves of the MPPT controller at various voltages (I think Morningstar publishes theirs) which has a big impact on real world gained amps into the batteries.

The other thing which is hard to get info on is how a particular unit's MPPT actually does the tracking. From info available Rogue and MorningStar look decent (probably both a little slower than I would like to chase Vmpp in fast moving clouds but might actually work quite well), but it is possible to implement MPPT that yields only the battery amps that PWM would in some conditions, or even yield less than PWM (say some panels in building shade and the controller trapped optimizing the wrong voltage peak or, fast moving clouds in a mixed panel system, after a Vmpp setting of high voltage and no ability to follow the voltage down to the other lower max peak).

Jim

[BFL13]

Thanks for explaining that.

KJ, how do you think that 4210 40amper at $178 stacks up against the MS45 45 amper at $450 (not sure of all prices available on that one) for an array like yours at 550w?

[HiTech]

x2.

[KJINTF]

Just a guess it might boil down to a design parameter and parts costs

The 30 amp version - Can handle less power so with less of a internal heat issue they might have choosen different parts for the input stage which resulted in a higher max input voltage. Either way a 100 Volt max input limit should be enough for either system using a series parallel array connection.

[HiTech]

No.

First off ignore load limit. It is not normally used on RV solar setups and does not apply to sizing. I don't think you use the load terminals on your LandStar either. Typical application is solar lighting.

The specs just mean on the 40 amp unit you need more panels in parallel and fewer in series to stay under the total Voc. The Voc does not determine the power capability of the unit, just the panel wiring. The capability is determined by total watts it can handle, and amps it can put *into* the batteries.

A higher Voc buys you more flexibility in how you can wire your panels together, but that's about it (unless Voc is so low it is below the Voc rating of a *single* panel you want, which is unlikely).

For controller sizing purposes, it is easier to just think of the MPPT panels all wired in parallel.

Jim

[BFL13]

pianotuna wrote:
Hi BFL13,

The input voltage limit does not change the output of the controller. I.e.

30 amps X 12 volts = 360 watts output, 40 amps x 12 volts = 480 watts.

Since it they are both MPPT you could feed them with up to 150 volts for the 30 amp and up to 100 volts with the 40 amp.

I.e.

150 v x 2.4 amps = 360 watts for the 30 amp

100 v x 4.8 amps = 480 watts for the 40 amp

BFL13 wrote:
I got lost again how the 40amper could do more watts than the 30amper but with 100v limit where the 30 has 150. So picking panels and arranging your strings and parallels must be a tricky business. ?

The 3215 has 150v max input but can do 12v/390w and 24v/780w
The 4210 has 100v max input but can do 12v/520w and 24v/1040w

They each have max batt v of 32v, have same load limit of 20a but battery current is 30a and 40a (spec sheet for each in links)

Doesn't that mean the 30 amper can have more total Voc and so more panels, but they have to be smaller to not go over the watts limit?
Seems backwards to me.

[HiTech]

Exactly. The voltage limit on MPPT is no different than staying within the voltage limit on a PWM controller.

Jim

[pianotuna]

Hi BFL13,

The input voltage limit does not change the output of the controller. I.e.

30 amps X 12 volts = 360 watts output, 40 amps x 12 volts = 480 watts.

Since it they are both MPPT you could feed them with up to 150 volts for the 30 amp and up to 100 volts with the 40 amp.

I.e.

150 v x 2.4 amps = 360 watts for the 30 amp

100 v x 4.8 amps = 480 watts for the 40 amp


btw I'm not recommending series panel strings--just showing some "what if" numbers.

BFL13 wrote:
I got lost again how the 40amper could do more watts than the 30amper but with 100v limit where the 30 has 150. So picking panels and arranging your strings and parallels must be a tricky business. ?

[HiTech]

It's not too hard. You can just do them all in parallel and not worry about the voltage limit, or do in serial until you would hit it, then start paralleling, as 2 examples.

Jim