PV Array as voltage clamp for Hydro/MX60

frserapheim · March 2010

Hi all.

I am wondering if someone can help me here.

I would like to wire my Stream Engine in parallel with my MX60 / PV array. The PV array is made up of 3 X 3 Sharp NUS030E panels - specs -
Pm 180w
Voc 30
Vpm 23.7
Isc 8.37
Ipm 7.6
aVoc -104

Since their connected 3 X 3 - that gives an Voc of 90 vDC with Vpm of 71 vDC and PM of 1620 watts (if my maths are ok).

My battery bank is 24 vDC, 3300 Ah/100.

The stream engine has 2 nozzles and is wired parallel delta. I have access to 2 water sources, that run mainly at nights but sometimes during the day.

The first water source is 1 l/s. The penstock is 40 mill and 250 meters approx. When working the pressure gauge shows 200 PSI! The supplied power at the batterys is 525w as measured by an Outback FNDC battery monitor / shunt.

The other water source is 2 l/s. The penstock length is 100 meters of 50 mill and 150 of 40 mill. I dont have a pressure gauge on this line but the battery monitor shows about 250 watts when charging.

At the moment the stream engines rotor is quite a distance from the stator - tuned to provide the most power with our first water source.

Can anyone help me with details about what I need to do to safely connect the turbine to the mx60 without damaging my PV array? I would like to use the mx60 mppt function for the turbine.. what would happen when the mx60 does its sweep though? What else should I do to protect the turbine/mx / pv array.

Sorry for the long winded question and for any errors... im still on the lower end of the learning curve.

Thanks
serapheim

BB. · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

My question for you--Most water turbines require a constant load to prevent turning too fast (no electrical load, speeds up until damage occurs or water flow is shut down). Also, many alternators do not have voltage regulators and when the load/current is removed, they can generate a lot of voltage (possibly 100-150 VDC or more).

A MPPT Solar Charge Controller is normally installed with solar panels such that when the battery bank is fully charged, the Solar Charge Controller stops taking electricity from the solar panels. So--when the battery is full, the turbine could damage itself by over speeding and/or damage the solar array/Charge Controller by over voltage (Outback has 150 VDC maximum input voltage).

Normally, a water turbine is tied directly to the battery bank (always a load present). And the charge controller is also connected to the battery bank and configured as a "dump controller" and the output is connected to some electrical load (like a large resistance heater).

When the battery is "charged" the dump controller turns on the electric heater for a while until the battery needs charging again--then the dump controller turns off...

There are other ways of doing things (regulating water flow to adjust output current/voltage)--But not many that I have seen for smaller installations.

Note: I am not an expert in this.

-Bill

frserapheim · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

Bill thanks for your reply and comments.

Yes your quite right. Actually I didnt wish to make my original question so long winded so I did skip some information which I probably should have included now that I think of it

I think they might answer some of your questions.

I currently have 3 seperate relays (from Outback inverters / MX60s) safegaurding the batteries from overvoltage from the hydro -

2 dump loads at 27.6 vDC of 500 watts and another dump load at 28.2 of 500 watts
1 electronic solenoid which disconnects the hydro at < absorb voltage.

So battery wise I think Im safe

The voltage clamp /regulator on the turbine is where I am not so sure. I have read elsewhere that this has been done using this method... I just dont know if my system would fit the "criteria" for being safe. The turbines wired parallel delta and the systems 24 vDC so I am "hoping" that I would be within the MX60s voltage range. Unfortunately I do not know enough to calculate what the VOC of the stream engine would be with my site. I was also hoping that the PV array would clamp the voltage at its limit ie 90 VOC. :roll:

Then there is always the issue of something going wrong with the controller like someone had pointed out to me

I havent thought of what I would do in that scenario yet

I was hoping that someone that may have done this could chime in....

Thanks again
serapheim

mike95490 · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

Is there a way you can switch off the water flow on the turbine, when the batteries get full? That'd save some bearing life.

sawmill · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

I use a MX60 with a small hydro unit into a 24v bank. If you are going to run your hydro unit in parallel with solar the hydro's unloaded voltage can not exceed 140v with 150v being destructive. If you do not know the unloaded voltages of your units it is quite simple to check with a good quality meter. Disconnect the hydro from the battery, allow it to spool up to its maximum rpm, check this voltage, if it exceeds 140v you will be risking the MX60.

The MX60 really works great with my small unit(pma). My unloaded voltage is 138v, the controller uses 40% of this voltage as its lock on. This tranlates to 56v from the hydro to the MX60 which is then converted to the battery voltage. I'm sure your situation is different and will require careful thought on your part. I think the mx will work fine for what you propose if the voltages do not exceed the Outback figures.

frserapheim · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

Mike,

I have an electronic valve which disconnects the hydro at < absorb voltage. This usually only occurs if the hydro is running in the day and the PV is charging. Your quite right, no use wearing the hydro unit when you dont have to.

Sawmill,

thanks for the info. I am (was) a bit afraid of of disconnecting the batteries to test for the hydros VOC. I suppose a few seconds wouldnt hurt but I am still concerned since the unit works at 200 psi! / 13 bar! A chart in the stream engines manual says thats about 4200 RPM!!! I dont know if thats when the turbines load / unloaded though.

I am also "guessing" that the VOC should be less than the MX60 max voltage of 140 vDC since I have rewired to parallel delta. I suppose the only way to really find out is try? Although it would be nice if someone could provide the maths :roll:

Also, can you tell me what parameters your using on the MX60. Do you allow it to sweep or is it parked at a certain MPPT that you have set? Also what is your PMAs air gap? Any information would be extremely usefull.

Thanks to all for replies..
serapheim.

BB. · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

Can you talk with the company that made the turbine/alternator?

I assume you have diodes/full wave bridge to change the AC into DC output. Any over voltage (no matter how short) is enough to damage the electronics.

Find out the maximum voltage of the diodes first. Then, you could shut down the water, disconnect the alternator. connect your meter, slowly open the water valve and watch the voltage as you open the valve more and more. You should be able to see if voltage is going to become too high and shut down the water if it approaches an unsafe voltage.

-Bill

sawmill · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

The MX60 snooze mode is disabled, the sweep interval is set to 00 minutes, I use the 40% park mpp setting which in my case gives the most wattage. Usually the manual set 40% value gives me a little more wattage than if I allow the MX60 to auto select the mpp value. You do not want to auto sweep when using a hydro unit through a MX60, there is no reason to sweep because unlike solar your power stays the same.

I use a dual rotor 24 magnet pma. Upon powering up, my unloaded voltage was
165v. I had to increase the air gap( by trial and error) until my unloaded voltage was below 140v before connecting to the MX60. Bill has given excellent advice on safely checking your unloaded voltage.

All hydro situations are different and unique, no two alike, and require careful operation. When checking these unloaded voltages you probably will be in a wet damp enviroment which can be exciting when dealing with dc in excess of 100v. I suspect with your 200 psi you will have voltage and amperage that requires the upmost caution. DO NOT connect your MX60 to a hydro unit until you are sure of the unloaded voltage.

frserapheim · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

BB,

thanks for the advice! The overvoltage limit of the bridge rectifier is not something that I had thought of. I will try to contact the manufacturer for specifications.

Sawmill,

thanks for your system information. Actually I would like to leave the MX60 find the MPPT value itself if possible. Again, we have access to 2 water supplies of differing head, water flow and as things stand at the moment I can only tune for 1 of them. If I could get this to work, I will simply leave the air gap low enough not to overlimit the MX and leave the controler find the "best" match.

Just for interest, what gain have you seen from the MX60 over not connecting straight to the battery?

Thanks again for responces...
serapheim.

sawmill · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

Since you appear to have more hydro output than you can use 24/7, ie having to use dump loads to prevent overcharging. Your situation begs the question of why the desire to use a MX60. It would appear your hydro output should be reduced to allow a more balanced system and also reduced wear on your units.

I suspect your Stream Engine PMA operating unloaded with 200 psi will far exceed the MX60 voltage limits. My small PMA with only 9.5 psi obtained 165 volts before the air gap was increased to allow tying to the MX. To answer your question about direct connecting to the battery, the amperage is almost cut in half as opposed to using the MX in my situation. Plus I have less line loss at 56v rather than 24v coming 300 feet. I am only dealing with a max 120 watt output so I am trying to get every watt available.

Your hydro potential sounds like something most of us can only dream about.

frserapheim · March 2010

Re: PV Array as voltage clamp for Hydro/MX60

Sawmill,

yes we are quite lucky here! But the hydro does not always run, and there are times when we do need its full output which is why I thought of the mx 60. If the water sources ran 24/7 then your comment on tuning for a more balanced system is definitely the best option. At the moment however the water sources run irregularly and not always at the time we want them as they are not in my control.

The dump loads are there for safety messages - there just in case something goes wrong.

Actually the whole point of using the PV array in parrallel with the hydro is just this - to allow that MX60 to sweep without the hydro going over the chargers max vdc rating. Others have successfully clamped the hydro using the PV array. The theory is the array works as a big zener diode, clamping the hydros vDC to a the panels VOC. It is definitely rare but it has been implemented successfully by others from what they say. I am simply looking at more information of what to look our for.

There is a similar thread over at the microhydro group where I also got mixed responces for anyone interested.

Thanks.
serapheim

PV Array as voltage clamp for Hydro/MX60

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