Dump load, needed or not?

[Ptom]

I should know this....but I am coming up blank. My system, 24 VDC, currently (pun intended I guess) uses a dump load, a 1000 watt bank of resistors, and a 60 amp MorningStar PWM controller/ load divertor that decides when to divert incoming power to the dump load. and has for years, mainly to keep my grid tied hydro under control when the grid goes down. It has worked fine for 15 years, in the rare times and for short periods, the grid has gone down here.

But I recently added a additional, winter time only use (when the hydro is down) 1000 watt PV array to my existing PV array, again, all grid tied via a Outback inverter and a token /minimal battery bank. Now I am putting out as much as 105 amps, obviously in excess of what my divertor AND my resistor bank can handle, but the difference is, unlike the hydro's input, which goes right into the battery bank, the PV arrays first go thru a charge controller, 2 actually. So....., if the grid goes down (which I replicated this morning by throwing a breaker) will the controllers continue to allow incoming power to the battery, overcharging it in short order, frying it (sealed AGM types)? Or, will the controllers "control" the voltage rise by the removal of the load, by shunting the power away before it reaches the batteries?

My normal voltage, which is the voltage the batteries float at, any excess being sent into the grid, is 26 volts, it went up to 30 instantly, and of course the resistors started heating up. At this time of the morning, the system was only producing 55 amps, about half of it's max.

A fix, if one is needed is another dump load and another divertor. Another fix, if for the grid not to go down, at least during the day, but that's wishful thinking of course.

 

[timselectric]

I'm assuming that you have the SCC's connected to the batteries. They should be able to be set for the type of batteries you have. And only charge to full.
After that, they just stop pulling power from the panels.

 

[Ptom]

Yes, both charge controllers are of course linked to the battery. Though I did see 30 volts, it did not as a matter of fact go higher then that. Though I concluded the experiement only a few minutes later. And,now that I think about it...., out of the mish/mash of odd ball PV panels I have, in addition to the two 1000 watt arrays being the primary ones and controlled, I do have a 250 watt module (two 125 watt 12 v.) that I just hooked up direct to the battery, no controller at all. So a few amps incoming from that would continue in, but nothing the existing divertor and dump load couldn't handle.

 

[timselectric]

That's a very odd setup. But if it's working for you then great.

 

[LittleLebowski]

I’d like to see the hydro setup.

 

[Rednecktek]

Solar doesn't need a dump load but DOES need a charge controller. The charge controller will just stop pulling power that isn't needed and if it's in parallel with the hydro controller it doesn't even know the hydro is there. The controller will turn the PV power into Battery power just fine, that's its job. ?

 

[Ptom]

Solar, or hydro, when used in my application, does not need a charge controller! That's what confusing me, as the Outback inverter I set up (15-16 yeas ago, and I would have to learn how to do it again) to basically act as a divertor: once the battery is at the setpoint, 26 volts, any further power gets sent to the grid. IF this was a conventional off grid system, my question would never arise, as we well know that the batteries would just float, no mater how much "extra" power was available. Keep in mind, my hydro is totally "uncontrolled", the inverter does it's thing, acting in effect like a controller, same with the one 250 watt panel I have, direct wired to the battery, no controller used or needed. The main reason I have dual controllers for the two arrays is because they are 150' away, and wired for high voltage while in transit, and I needed a controller capable of stepping it down to the battery voltage. A side benefit is the usual efficiency increase with a MPPT , over PWM, especially during cold weather.

My brief experiement of shutting down the inverter's access to the grid, pretty much tells me I DO need a larger/another dump load and another divertor. Why else would my dump load be getting quite hot, and quickly, that doesn't indicate to me that the controller was shunting power, it was happily maxxing out the load dump, with the excess instantly bring the battery up to 30 volts. I'd prefer to see a properly sized load dump, or two, running at a fair bit less then max dumping capacity, and the indicated battery voltage staying around 26 volts, or at least not 30.

My next test, unlike this one, where I was inputting 1200-1300 watts or so, maxxing out the dump load rating of 1000 watts, (no wonder it got hot so fast, while the battery voltage jumped) next time I will shut down enough of the incoming power to keep comfortably withing the state capacity of the dump load. In effect, that will replicate what would happen if I add more dump load and another divertor. Everything tells me the MPPT controllers are NOT shunting incoming power, though otherwise operating properly, it's the "uniquness" of this inverter setup that is seemingly indicating the need for more dump load. I don't think I have a problem, at least one that needs me to meddle with a system that has been working great, just that with this recent increase in power, I need a similar increase in dumping capacity.

 

[SamDeleted]

@Ptom ,

Did you get this sorted ?