Load ports are battery voltage. They vary with the battery. If there is solar available, then the device's load on the battery, and the subsequent drop in voltage will be compensated for by the solar. This behavior is IDENTICAL if the load is attached AT the battery or AT the load ports.
Forgive me citing this old post, but I have a question that I've been asking for some time (a little of it here, mostly to Google searching). However this above strikes me as not fully correct. This is how I see it:
- Load ports may be battery voltage (they may also be from the panel as the poster indeed goes on to suggest)
- the behaviour is not in my experience identical comparing if the load is attached to the battery or to the load port. I have definitely seen this in the actual measurements I've taken on my setups. Perhaps this is controller dependent.
I've noted that a "shunt" is often used here (on this forum and perhaps in this "domain") to simply monitor the current in and out of the battery. Its been a while since I studied electronics at college (electronics engineering, but did my specialisation in computer systems) but what is called a Shunt here is also known to me as a Ballast Resistor.
I propose that inside a Solar Charge Controller (SCC) {perhaps especially an MPPT type} which has a load uses a Shunt internally to ramp up the panel to compensate for the load in as much as the panel can (or to the limit of its rated capacity).
I believe that this is actually a more ideal way of handling minor loads (loads being a demand for electricity) on the system because then the SCC can continue charging the battery in a more "ideal way" to fully groom it to go into the night. If it goes into the night without this situation then it is going to lead to the battery perhaps not ever reaching a float level (thinking Lead Acid here, not Lithium chemistries) which will lead to battery plate sulfation.
It seems to me that without a shunt to know whats going on a in terms of load, a SCC can not compensate for that change in power demand by simply looking at the voltage drop of the battery (or if there is please do share that with me).
As an aside it was mentioned somewhere here that it is not ideal for the SCC to actually manage this because "why put another source of heat in the SCC". However MOSFET switches are very effective, Let me cite a reasonable source (
here) :
Another approach to switching DC loads is by employing a transistor. Modern MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) can switch very fast, don't suffer arcing problems and require negligible energy to switch states. They are also a fraction of the size of a relay. As an example, an Infineon BSC030P03NS3GAUMA1 MOSFET is only 5mm wide, 6mm long and 1mm high yet it can switch 100A and would only burn 23W doing so, it barely even needs a heatsink!
So if a SCC has a MOSFET in it to do the load switching of a mere 20A it strikes me as a good design feature. Just working with that 20A limit (no reason why it can't step up) a 48V system will give a load of 980W (at its limit) which in an RV or smaller off grid situation is nothing to be sneezed at. Sure it won't power a fan heater (2000W) but will amply power a domestic fridge of reasonable size (I've measured my mates two door fridge freezer and it seems to peak at 600W and consume about 1kWh over 24 hours).
So unless I'm misunderstanding things it seems we should be using shunts in our systems to feedback into the SCC the actual demand so that they can (panel capacity and weather permitting) suck that load current out of the panel and keep the battery on its charging trajectory by stepping up the amps its providing. Indeed this is something I think I see in the more complex arrangements that Victron offers in products
like this.
Anyway, if
@snoobler isn't active anymore, perhaps someone else has thoughts on this, because while this seems right to me the devil is often in the details I didn't know.
Thanks