Load connection on charge controllers

Chark · October 2015

I have a question about how charge controllers work, specifically the load connection.

Suppose the battery connected to the controller is fully charged and the solar panel is producing power that is not being stored. If I connect a load to the battery it obviously (I think) draws current from the battery that will not be replaced until the controller goes back into charging mode. If, however, I connect a load to the load terminal on the controller, does it use current available from the solar panel or does it also only draw current from the battery?

Is there regulated voltage at the load terminal of the charge controller when no battery is connected?

I am considering a small portable system without much excess battery capacity where having the battery fully charged at sundown may be important.

Thanks for your input!
Chark

waynefromnscanada · October 2015

A good (real, not a toy) charge controller will go into FLOAT mode once the battery is fully changed, so as to maintain a battery voltage only high enough to keep the battery charged without overcharging it. At that point, any load on the battery will be supplied by the Charge controller, assuming conditions and ability of the panels to supply the power being used.
That said, we don't know what you have for a charge controller, make and model.
OH, and since you are so far only considering a system, the key is to start by determining what your expected loads will be, bearing in mind that loads grow with time. The next step is to determine the battery capacity needed to sustain the expected load. FINALLY, comes the size of solar panel needed to properly charge your battery bank.

oil pan 4 · October 2015

Chark said:

Is there regulated voltage at the load terminal of the charge controller when no battery is connected?

I am considering a small portable system without much excess battery capacity where having the battery fully charged at sundown may be important.

I believe I have read that most charge controllers do not work when no battery is present.

Always go bigger then you think you need on the battery.

mike95490 · October 2015

The load terminals on most charge controllers has both:
Limited current (amps) rating
LVD (Low Voltage Disconnect)
and it's connected to the battery via a MOSFET & fuse.

As long as the solar PV panel can supply the load, the battery will not be depleted. When the load exceeds what the panel can harvest, the battery makes up the difference,

Chark · October 2015

Thanks all. It's less complicated than I was thinking.

(waynefromnscanada, I don't have any of the pieces yet, trying to make sure I understand what I need first.)

I was thinking there was an advantage (other than LVD) to connecting the loads to the load terminal on the charge controller, rather than the battery, and that I should make sure it could handle the current to the loads. It sounds like that is not the case and it only needs to be sized for the current from the solar panel.

Thanks again.

inetdog · October 2015

Chark said:

Thanks all. It's less complicated than I was thinking.

(waynefromnscanada, I don't have any of the pieces yet, trying to make sure I understand what I need first.)

I was thinking there was an advantage (other than LVD) to connecting the loads to the load terminal on the charge controller, rather than the battery, and that I should make sure it could handle the current to the loads. It sounds like that is not the case and it only needs to be sized for the current from the solar panel.

Thanks again.

Normally you do not "size the LOAD output" of the CC to anything. Instead you decide why you would ever want to connect any loads directly to it (usually for LED night lighting) and plan on using output to drive a relay if you have any significant loads (like your inverter) that you want LV protection for. As noted the LOAD output will supply loads from the battery if the CC is not producing enough current to cover the load.

zoneblue · October 2015

The load output (usually only available on small controllers)(T60,TS60 are exceptions) (and you can never run inverters or other high current loads off load terminals) are only generally used on tiny standalone systems, such as a that which powers an electric fence, or remote security gear. The point is small systems that are less supervised can be made to LVD prior to doing chronic damage to the battery. But watch out that not all controllers with load ports have LVD. The morningstars are a good example, if that feature is important make sure the exact model has LVD. Also check the actual LVD voltage. Depending on the battery it can either be too low to be of much help, or false positve trigger on peak loads.

But in general for the average system, load ports are of almost no use, because our loads are much greater, or arent present at all on any half decent controller, for the same reason. Instead they have AUX ports which you can power relays to acheive similar things.

Load connection on charge controllers

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