Two parallel C40's

[Warren]

Hello,

The grid does not exist where we live so we have been producing our own power since 1990 with an early ES&D Delco alternator hydro system. I have just upgraded to a 2hp 3 phase induction motor, step down transformer, rectifiers and two C40 controllers in diversion mode, dumping into two separate 600 watt water heater elements. This 12 volt system currently produces 50 amps but I can increase it to 60 amps with different taps on the transformer. Until I have the controllers running properly I am keeping the current at 50 amps. The amperage is constant regardless of whether the voltage is at the float of 13.8 or absorption of 14.1 volts.

Initially I thought the two controllers should be set at the same Bulk and Float settings in order to operate together but quickly found this was not so. My best success was to try to balance the output currents of both controllers by adjusting the Bulk and Float settings on one controller. Part of the time both controllers will be in Absorption or Float mode together, the rest of the time only one controller will in Float mode. It is not always the same controller either.

Is it possible to get both controllers operating together all the time?

The other problem is the current going into the controllers is not the same for both controllers when they are both in Float mode. There may be a difference of 10 to 20 amps even though the controllers are fed from the same point.

Has anyone noticed this and is there an explanation why the difference?

For those who question whether it is recommended to operate two C40's in diversion mode, it is mentioned in the owner's manual on page 66 in the trouble shooting section.

All comments are welcome. My upgrade was made easier through the postings from this group. Thanks,

Warren

[Volvo farmer]

If your maximum current is 60A, couldn't you just replace the dueling controllers with a single C60? I think Morningstar or someone has a dump controller rated even higher than 60A should the need arise.

I've got a C40 and an MX60 on different solar arrays but the same batteries and it is interesting to watch them interact with each other. I consider the C40 the dumb controller and the MX60 the smart one. If I set the C40 too high in absorb or float, it messes up all the nifty daily logging of the MX60 and it makes me mad, cause the dumb controller won't tell me how long I floated batteries today.

If you have only one charging source, I think the easiest solution is to find a single controller. Two C40s have more Ebay value than a C60 anyway. With two charging sources, it's easier to make one controller the master and the other the slave. Things seem to get complicated in my book when both controllers are trying to charge batteries off the same source.

 

[jmk]

You have to set one controller so it's at a little bit higher voltage than the other one on booth float and bulk settings.

[Warren]

Hello,

jmk, I had thought of setting one higher than the other but think this would only work if the diversion loads more closely matched half the output of the system. Otherwise the controller with the lower setting will attempt to divert more current than it was made to handle.

If I can't get the controllers operating together, I am thinking of lowering the diversion loads to 450 watts and having one controller set a bit higher than the other.

Volvo, the C60 can't handle 60 amps continuously according to the NEC recommendations. I wanted a controller around 80 amps to give some measure of safety to the system but did not find anything except one that used mechanical relays.

Thanks,

Warren

[scoraigwind]

"the controller with the lower setting will attempt to divert more current than it was made to handle."

this is not true.

The amount of current the controller diverts is limited by teh size of the diversion load.  It is important to choose a load that cannot overload the controller.  for a C-40 I would choose a load that draws about 35-40 amps at 15 volts.  that is safe.  for a tristart (much prefered) the load can have a lower resistance).

Set one tristar to do the controlling and the other one at a higher voltage (one step higher) so that you have a backup.  In exceptional conditions the first one's heater will be fully on, and the voltage will rise then so the second one comes on.

[TomW]

Hugh;

Thanks for clearing that up. I was starting to wonder if the C-40 could somehow trick the "load" into drawing more amps and bypassing normal physics somehow? I was not sure so I just waited for more responses. I had a C-60 at one time but never used it for load or diversion control just in charge control mode.

I like the trick you mentioned for the Tristar, also. Is there a reason the Trace can not do it that way?

Personally, I would sell the 2 C-40 and get a single unit to do what I needed but thats me.

Thanks for sharing.

Cheers.

TomW

[Warren]

Hello,

Hugh, I was worried my diversion loads were too large for the C40's and that would lead to too much current through one controller.

TomW, I agree one controller would be simpler but there are other complications to my hydro system which could allow the amperage to exceed the specs of the Tristar 60. To put it simpler, I am not running at the maximum amount of power for the system even at 60 amps.

Life is better with complications,

Warren