Provide PV input to controller from DC power supply?

unyalli

With a midnight classic 150 and wizbang I have a very advanced battery maintainer. When sun is not cooperating, and I must run the generator, Instead of charging the batteries with a out of band charger like my RV converter could I provide the controller with power via a small DC power supply? I imagine it would be on a DC breaker like the panel strings and the panels would be switched off THEN the power supply switched in. Would MPPT sweeps aggravate the power supply?

I'm thinking about this unit http://www.meanwell.com/search/RS-150/RS-150-spec.pdf

-Jeff

Cariboocoot

Re: Provide PV input to controller from DC power supply?

Not recommended.
The output from DC supplies is not as 'clean' as the output from PV. The charge controller may be damaged.

jonr

Re: Provide PV input to controller from DC power supply?

I expect that the charge controller would attempt to draw more power from the small power supply than it can deliver and the supply would shut down. But maybe the charge controller can be told to limit power draw. Or some supplies can be current limited and will continue operating, just at a reduced output voltage (ie, more like a solar panel).

In terms of damage to the charge controller, I'd ask Midnite Solar. Knowing the way that buck converters work, my guess is that it would be fine.

Cariboocoot

Re: Provide PV input to controller from DC power supply?

jonr wrote: »

I expect that the charge controller would attempt to draw more power from the small power supply than it can deliver and the PS would shut down. But maybe the charge controller can be told to limit power draw.

Yes, it can. Program the output limit to less than the supply's maximum.

In terms of damage to the charge controller, I'd ask Midnite Solar.

Good idea. So boB; changed your minds on this?

Blackcherry04

Re: Provide PV input to controller from DC power supply?

unyalli wrote: »

With a midnight classic 150 and wizbang I have a very advanced battery maintainer. When sun is not cooperating, and I must run the generator, Instead of charging the batteries with a out of band charger like my RV converter could I provide the controller with power via a small DC power supply? I imagine it would be on a DC breaker like the panel strings and the panels would be switched off THEN the power supply switched in. Would MPPT sweeps aggravate the power supply?

I'm thinking about this unit http://www.meanwell.com/search/RS-150/RS-150-spec.pdf

-Jeff

I have two IOTA's set up on a couple xantrex c-35 Controllers ( PWM ). The IOTA's are cranked up to 15.5 volt output and they work perfect. I have never tried them on a mppt, but it only sweeps in Bulk so it should not be that big of a issue as the charger transitions to absorb. In fact I was just looking at a " Kid " to mate up with another IOTA charger I have. I need something with long absorb hours with a shunt for ending amps.

I'll post back when I get one.

vtmaps

Re: Provide PV input to controller from DC power supply?

jonr wrote: »

In terms of damage to the charge controller, I'd ask Midnite Solar. Knowing the way that buck converters work, my guess is that it would be fine.

That has been discussed several times there. First of all you don't want it to do MPPT... it may be stressful to find the maximum power point of a large power supply.

I think boB has mentioned the word 'stiff', as in if the power supply is too stiff you will damage the controller. It can be done. It has been done. I think the folks at Midnite recommend against it because they want happy customers, and using a controller this way doesn't always have a happy ending.

--vtMaps

stephendv

Re: Provide PV input to controller from DC power supply?

I was thinking along similar lines the other days except to DIY a simple DC power supply, e.g. transformer on the 110V generator output to bring it down to 55 ish volts then rectify and add a capacitor to smooth the output then feed to the midnite controller.
You can pickup 220V to 110V 3kW transformers for around $80, so surely it could be used to transform 110V to 55V? After rectification that should be 77V DC. Doable?

Cariboocoot

Re: Provide PV input to controller from DC power supply?

This points back to the idea of feeding a Classic 250 with rectified line current and using it as a 'direct' charger (the attraction being the superior charging regime). Sure would be simple to use one controller for PV and gen charging both!

But there's the trouble of getting the AC 'clean' enough. As far as I know no one has been willing to risk a $600 controller to find out if this is viable. Not sure the folks at MidNite have tried it. Haven't seen them say "it's okay to do this" either.

BB.

Re: Provide PV input to controller from DC power supply?

Given that some folks feed rectified (probably 3 phase) AC from wind/water turbines to their MPPT controllers, and others feed 24 volt battery bank to a MPPT controller to their 12 volt battery bank... It does not sound like it is the end of the world to put on some sort of AC converter/charger to the front of an MPPT controller (all else being equal--I.e., AC converter/charger can run at current limited rating).

However, when the designer of one set of MPPT controller series says he would not--I would have to respect that he knows his product better than most folks.

-Bill

Cariboocoot

Re: Provide PV input to controller from DC power supply?

Curiously the AC from a wind/hydro turbine can be a lot cleaner than that from the grid. Utility power can have quite a lot of distortion on it.

mike95490

Re: Provide PV input to controller from DC power supply?

BB. wrote: »

Given that some folks feed rectified (probably 3 phase) AC from wind/water turbines to their MPPT controllers,....

3 phase AC, rectified , has much less ripple than single phase rectified. Single phase will need filter caps and maybe ballast resistors to save the diodes from blowing out as the peaks charge the caps.

inetdog

Re: Provide PV input to controller from DC power supply?

stephendv wrote: »

I was thinking along similar lines the other days except to DIY a simple DC power supply, e.g. transformer on the 110V generator output to bring it down to 55 ish volts then rectify and add a capacitor to smooth the output then feed to the midnite controller.
You can pickup 220V to 110V 3kW transformers for around $80, so surely it could be used to transform 110V to 55V? After rectification that should be 77V DC. Doable?

The problem here is that a generator is not designed to have the load keep increasing the power draw until the generator engine starts lugging or the voltage sags by 50% because of resistance losses in the windings.
The output of a wind generator, like the output of a PV array, is inherently limited and the wind generator is in fact designed to be loaded down until the turbine speed starts to fall.
Running a simple charger off any kind of stiff AC supply is fine. Trying to use an MPPT input is where the problems arise, big time.

And even for a wind turbine, as the folks at Midnite will tell you, the optimum way to handle the input to the CC is for the CC to base its current load on the Voc of the turbine, using computed tables, rather than trying to use a search algorithm to find the MPP.

Among other things, the voltage output of a solar panel will change instantly when you change the load current. But for a wind turbine you have to wait to see what the new equilibrium turbine speed is before you know where you really are on the I/V curve. That takes too long for a practical pure MPPT algorithm and does not work at all with varying wind speeds.

jonr

Re: Provide PV input to controller from DC power supply?

inetdog wrote: »

The problem here is that a generator is not designed to have the load keep increasing the power draw until the generator engine starts lugging or the voltage sags by 50% because of resistance losses in the windings.

But the controller can limit power input such that the generator/transformer never lugs or sags by 50%. At that point, the controller can attempt to find a MPP without causing any problems for the source.

inetdog

Re: Provide PV input to controller from DC power supply?

jonr wrote: »

But the controller can limit power input such that the generator/transformer never lugs or sags by 50%. At that point, the controller can attempt to find a MPP without causing any problems for the source.

Absolutely correct. Which is why the general question of whether a DC supply can be used as input to a CC depends entirely on the design of the CC. And with some manufacturers, good luck in getting that information.

Cariboocoot

Re: Provide PV input to controller from DC power supply?

inetdog wrote: »

Absolutely correct. Which is why the general question of whether a DC supply can be used as input to a CC depends entirely on the design of the CC. And with some manufacturers, good luck in getting that information.

Another example of using equipment for a purpose other than which it was intended. Why would anyone expect the manufacturer to anticipate such usage? Maybe you want to use your inverter as a post driver; should they say that's okay so long as you use a solid ash handle?

Never expect things to work right if you use them wrong.

inetdog

Re: Provide PV input to controller from DC power supply?

I completely forgot about the need for the solid ash handle.
Might fiberglass be OK in a pinch?

Cariboocoot

Re: Provide PV input to controller from DC power supply?

inetdog wrote: »

I completely forgot about the need for the solid ash handle.
Might fiberglass be OK in a pinch?

Check with your inverter manufacturer. Some recommend oak.

Vic

Re: Provide PV input to controller from DC power supply?

The MidNite Engineering folks have recommended against the practice of using some form of external PS as the input power source of their MPPT CCs, as a general rule.

And, as noted, much depends upon the nature of the PS.

Have used the venerable OB MX-60 MPPT CC teamed with an AC transformer, rectifier, filter caps plus a circuit breaker as a battery charger, run from a Honda EU3000is genset.

This has worked quite well over periods of many hours of charging. In this exact case, the output voltage of this external PS was very few volts above Vbatt, which may have helped the CC deal with things. No series resistor was required, and this combo could deliver about 2200 - 2400 watts of charge power to the batts.

This was a simple "solution", as the the MX-60 was already being used in the system as the Solar CC.

The MN folks did mention, that if one must try doing this with their MPPT CCs, that using a resistor in series with the PS DC output, limit the output voltage of the PS to very little more than required to allow the MPPT CC to operate well, use Legacy P&O on the Classic, and Legacy O&P for the KID CC.

Have used this approach with the MN KID, and an SMPS. Had tried using the limiting R, but with the PS used, this was not required, and the KID sweeps quickly, and the PS does not seem to be brought to its knees.

BUT, in general, it is good to listen to the Engineers that design these products.

MPPT CCs usually have capacitors on the Vin side. It is not good to "work" these caps with ripple currents, so, any PS that one uses (at one's own risk) should be WELL FILTERED, as noted previously.

YMMV, follow the label, avoid excessive use. And so on. Vic