Charge controller for solar + hydro

[Jake Jacobson]

Hi,

I currently have about 20amps @ 12v worth of solar panels, and a small hydro electric setup that produces about 4amps @ 12v, my charge controller recently got fried in a storm so am looking for a replacement.

I need something that can take both the Solar and Hydro at once, and divert excess power to a resistive load (such as a 12v heating element etc)

Does anyone know of such a product that can do this?

Thanks

Jacob

[Rob Beckers]

Hi Jake,

Any diversion controller will do what you're looking for, and many of the regular charge controllers can be used in diversion mode. For example, the popular TriStar series etc.

With a diversion controller the charging sources (solar, hydro) connect directly to the batteries, charging them. The diversion controller also hooks up to the batteries, and it monitors the battery voltage. It will divert as much current as needed from batteries to a diversion load to keep the battery voltage in check, preventing overcharging. When sizing a diversion controller it should be able to handle the sum of all charging sources, ie. 24 Amp in your case.

There's another advantage of setting things up this way: Since the controller is no longer directly connected to the charging sources, but to the very low resistance batteries instead, it is much harder to fry it through lightning or surges. The batteries will 'eat' those surges and for the most part not pass them on.

-RoB-

[Jake Jacobson]

Hi Rob,

Thanks for your reply, that puts it simply helps me make sense of what i need to do.

The Tristar 45 is about $350

I thought this might be a cheaper alternative:

http://cgi.ebay.com.au/80A-80-Amp-Wind-Solar-Diversion-Charge-Load-Controller_W0QQitemZ150381739026QQcmdZViewItemQQpt ZLH_DefaultDomain_0?hash=item2303733c12

Having it set to disconnect the solar on diversion, and dump the hydro load to this:

http://colemanair.us/vp_asp/scripts/shopexd.asp?id=599

Which would end up being bout $210


What do you think?


Thanks

Jacob

[Jake Jacobson]

like this:

http://ebay.ccssoftware.com/ebay/Images/DLC_HookupDrawing_Dual2-24.gif

[Rob Beckers]

Hi Jake,

The controller on EBay you linked to seems to be using contactors to switch the dump load on/off. Which means it essentially has just one setpoint, trying to keep the battery voltage from going too high. Those controllers do not do proper charge control, as in absorb - bulk - float charging. If you want to save money, take a look at the Xantrex C35. They go for around US$100; not sure what they cost down under but it shouldn't be too different. It's a solid-state charge controller that uses pulse-width-modulation, can work in diversion mode, and do proper charge control. Your batteries will thank you! :nuts:

-RoB-

[Jake Jacobson]

Can the Xantrex dual control both the solar and hydro at once though? all the ones i have seen can only do one or the other (charge control or diversion control)

[Jake Jacobson]

Or another option is to use a cheap regulator for the solar such as this:

http://www.rpc.com.au/catalog/regulator-apple-p-2831.html

and then the ebay or xantrex in diversion control for for the hydro

[Rob Beckers]

Can the Xantrex dual control both the solar and hydro at once though? all the ones i have seen can only do one or the other (charge control or diversion control)

Yes, you can do both at the same time with a single controller in diversion mode: There are two ways to use a charge controller in combination with solar. Either as a series controller (PV modules wire through the charge controller onto the batteries), or in diversion mode (PV modules are simply wired directly to the batteries and the charge controller keeps the battery voltage under control through a diversion load). The downside of a diversion controller is that you need a dump load, something you would not need when using a series controller. The big upside of a diversion controller is that you can tie all charging sources directly to the batteries (no controllers needed) and a single diversion controller takes care of the batteries.

-RoB-

P.S. To complete the story I should point out that there are MPPT charge controllers as well, and they work differently. An MPPT controller converts PV voltage (higher than battery voltage) to battery voltage, and loads up the PV modules in such a way as to get the maximum power out of them. That's different from directly connecting the PV modules to the batteries. MPPT controllers are more efficient, but also much more expensive. For the situation discussed above we're talking about direct battery charging, no MPPT involved.

[Jake Jacobson]

Ok but if i have the panels connected directly to the batteries they are not doing proper absorb - bulk - float charging is that correct?

[Rob Beckers]

Yes, they will.
The diversion controller will divert as much current from the PV modules as needed (to the dumpload) to force the battery voltage in a way that it follows the proper charge profile. That's the beauty of it, you can hook up many charging sources directly to the batteries and still have good charge control with just a single controller. That single diversion controller needs to be sized for the "worst case" though, so it can divert all the current coming from the charging sources when the batteries are completely full.

-RoB-

[Jake Jacobson]

Thanks for all your help!, looks like i will go with the xantrex/tristar or similar

I don't suppose you know anything about lighting protection to stop this happening again? just got the quote back from our inverter that was damaged as well in the storm $500 for repair!

[Rob Beckers]

Hi Jake,

As it happens I know a bit about lightning and lightning protection. I wrote a few Web pages about it (http://www.solacity.com/Lightning.htm). Unfortunately, good lightning protection that actually works is very expensive, more expensive than the price of the inverter, and in practice all you can do is mitigate the risk. Fortunately there is quite a bit you can do on that front, just don't expect it to be fool-proof. There is a page about that as well, just take a look.

By the way, a $500 repair bill is actually quite cheap. The inverters that were damage by lightning that I was involved with cost more to fix (There weren't too many, but I don't recall getting one done for less than $1,000).

-RoB-

[Jake Jacobson]

Thanks Rob i will have a read, i guess the best way is to unplug the inverter completely during a lightning storm!