MPPT regulator denier!

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MPPT regulator denier!

Postby jaahn » Wed Oct 05, 2016 3:25 pm

Hi :D
On another forum I go onto there has been a bit of discussion about MPPT solar regulators. I have put up my ideas for a person to get started on a van setup. This was then put up by someone else about regulators:
"It is deceiving to compare the operation of a grid tie solar controller to a battery charging solar controller, the operation is in no way similar. Grid tie solar MPPT boosts the voltage from the solar to match a set voltage, RV battery charging MPPT step down the voltage to match a varying battery voltage. 2 completely different functions that are in no way comparable, RV MPPT units can not boost voltage, they won't even function unless the solar voltage is much higher than the battery voltage, Victron require a minimum of 5v differential, easy for a dead flat lead acid battery as that only requires a panel voltage of 15v, but a battery up around the 13v mark requires in excess of 18v from the panels and it must be able to maintain that voltage under load, or the unit will drop out. Many reports across multiple forums where MPPT has failed to deliver on less than good solar days until the battery was nearly flat, then it would kick in. not good when there is only limited sun time left in the day. There is no such thing as an electronic device that doesn't waste some power, the more it has to do the more it wastes or actually converts to heat, if that wasn't the case then why do MPPT controllers have such big heat sinks and often fans that PWM controllers of the same capacity don't need so they don't have them?
MPPT may work ok for a 1kW plus system in a very cold climate, but not RV size systems in a very hot climate like Australia, they can not and do not produce more than a comparable quality PWM controller that is at far better price.

Match the panel voltage to battery voltage required and use a good quality PWM controller, spend the $$ left over on more solar, you will be way I front."

Any comments ??? :shock:
Jaahn
Last edited by Gordon-Loomberah on Wed Oct 05, 2016 6:06 pm, edited 1 time in total.
Reason: fixed spelling in subject
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Re: MPPT regulator denyer!

Postby davef » Wed Oct 05, 2016 4:37 pm

Generally speaking I would agree with most of it.

The issue in a hot climates is that PV Vmp must be lower or PV panel efficiency drops (at high temps), which reduces MPPT controller effectiveness, say with 70 cell 24V panels. If you have quite high panel voltage, like 2-4 times the battery voltage then MPPT is more effective, especially on long cable runs.

MPPT on 70 cell 24Volt panels gave me about 5% extra, not worth it. My new system is 60 cell 24Volt panels and the controller is ON/OFF ... not even PWM. Search <Electrodacus SolarBMS> he has a good explanation.

Good MPPT controllers can be 90-95% efficient and mine has a small heatsink, maybe it was way too small!
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Re: MPPT regulator denyer!

Postby davidg » Wed Oct 05, 2016 4:55 pm

For me the choice MPPT controllers depends on specific use (Check the Midnite KID) or for a PWM only controller (Midnite BRAT), however it is correct in one part and that is the DC battery MPPT controller generally do only work properly provided the voltage from the PV is higher than the battery voltage, however there are controllers like the Midnite solar that can be configured as in what is effectively PWM only, they're one of the most flexible controllers around for a battery controller.

However it is incorrect saying that Grid MPPT inverter only boosts voltage, that is not the case it will, but it depends on the string voltage being used they will either buck or boost, in general though any MPPT unit works better if dropping from a higher voltage to a lower voltage with increased current.
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Re: MPPT regulator denier!

Postby Quokka2 » Tue Nov 15, 2016 12:46 pm

Came across this thread while looking for a way to boost solar panel voltage. I have a 48V solar charge controller, a 48V golf cart and a spare 190W solar panel which would fit very neatly on the roof of it; only problem is the panel output is only 36V. Would a simple 2x or similar transformer do the job, or is a more complex solution necessarily involved? I've considered 4x 18V panels but would have to buy them, and may end up with lower wattage anyway.
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Re: MPPT regulator denier!

Postby davidg » Tue Nov 15, 2016 7:54 pm

Quokka2 wrote:Would a simple 2x or similar transformer do the job, or is a more complex solution necessarily involved?

Transformer NO, they work with AC only.

Try 2 x 190W panels in series that will work with a proper MPPT charge controller.
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Re: MPPT regulator denier!

Postby Quokka2 » Tue Nov 15, 2016 9:23 pm

davidg wrote:Try 2 x 190W panels in series

Way too big for the roof, unfortunately :| Looks like will have to find a boost device; haven't found one that will operate up to 36V in.
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Re: MPPT regulator denier!

Postby Gordon-Loomberah » Tue Nov 15, 2016 10:43 pm

As David said, transformers are for AC, you will probably need a DC to DC converter something like this: https://www.power-supplies-australia.com.au/rsd-200c

When you say a voltage of up to 36V, do you mean that is the rated Voc or Vmp of your panel?
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Re: MPPT regulator denier!

Postby Quokka2 » Tue Nov 15, 2016 11:27 pm

Thanks Gordon - this is a 36Vmp 190W house panel; fits the cart roof perfectly :)
Looks as though the RSD-200 would do the job (just), but almost as pricey as 4x 40W 18V panels. Will have to sleep on this one...
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Re: MPPT regulator denier!

Postby Quokka2 » Wed Nov 16, 2016 1:56 am

Closer examination indicates the RSD-200C-48 to be a constant voltage (48V) device - probably not up to driving a 48V solar charge controller. What I seem to need is a multiplier which would create the effect of 2 panels in series as David suggested, with the extra voltage but diminished current.
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Re: MPPT regulator denier!

Postby Gordon-Loomberah » Wed Nov 16, 2016 6:12 am

How about the non railway standard unit, the SD200C-48, used without the MPPT?
The input voltage range for it is a bit tricky with that panel though.
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