Solar controller amps vs. what goes in battery

[rslifkin]

Originally Posted by Thumbs Up

In a general sense though, stating that amps is amps is confusing because as voltage drops it does require more amps to deliver the same amount of work.

That's correct, although voltage drop may or may not actually cause higher amp draw. Some devices will draw more amps at lower voltage, others will just run at reduced power with the lower input voltage (drawing the same or even less amps).

[lmxr]

Originally Posted by SKMT

Do you know how much of a concern it is to possibly exceed the shunt rating by about 25% for half a second on engine start up?

I wouldn't worry about it. The shunt is heavy and will be able to absorb the heat with negligible temperature increase. The shunt voltage meter (which measures the voltage drop over the shunt) ought to be able to handle an above nominal voltage of around 65 mV (assuming a 50 mV shunt).

[team karst]

Originally Posted by Thumbs Up

.



If you have too much amperage for one shunt or it is impractical to run all the negatives through a single shunt, you can add a second shunt and parallel the sensor wires (stack the connectors) at the monitor. Just make sure that the milliamp rating is the same (usually 500 ma)

? Most shunts are 50mV, although there are others. Paralleled sensor wires makes no sense to me. These are essentially low Z voltage sources. Not to be paralleled.

[Thumbs Up]

Originally Posted by team karst

? Most shunts are 50mV, although there are others. Paralleled sensor wires makes no sense to me. These are essentially low Z voltage sources. Not to be paralleled.

I stand corrected. Shunts are designated by millivolts, not milliamps and commonly are 50 mv, not 500ma.

[jgrebe]

First time responder since I'm mostly a member to learn. However I am a solar engineer and haven't seen this point in previous responses. First thing you need to know is that when it comes to solar charge controllers, amps are NOT amps as some previous posts indicate - meaning that for a given amount of power, amps change with voltage (power = amps x volts). Measuring amps only gives you half the story. Most solar charge controllers these days are MPPT type controllers which means they change the voltage of the input to a different output voltage that produces more power (maximum power point). Therefore is is very common for the amps of the input to the charge controller to be substantially different than the output amps. Measure both the input amps and volts then the output amps and volts and the power of the output should be about 95% of the input. If not you have a problem with meters or the charge controller

[donradcliffe]

The original post was not about amps in vs amps out on his MPPT controller, it was about measured amps out vs measured amps in at the battery shunt, downstream of the MPPT. In this case, Kirchoffs law says amps into any circuit junction must equal amps out. The resolution was that there was another branch circuit (the starting battery) where the current was not being measured.

I just tell beginners that MPPT controllers are "magic boxes", which do not follow Kirchoffs law.

[noelex 77]

Originally Posted by jgrebe

Most solar charge controllers these days are MPPT type controllers which means they change the voltage of the input to a different output voltage that produces more power (maximum power point). Therefore is is very common for the amps of the input to the charge controller to be substantially different than the output amps.

But input current is always less than output current (unless you have one of the extremely rare controllers that can boost voltage).

The OP is reporting the solar controller is indicating a substantially higher current than the battery monitor. This shows an error or a fault. If the controller was reporting the input current, the error or fault would be more, not less substantial.

[jgrebe]

I beg to differ but that is not what the OP asked. He asks about the different amps going into the battery versus the amps displayed on the controllers."Is it normal for the actual amps going into the batteries to be 30% less than the amps displayed on a solar controller?"no mention of a shunt controller. His question regarding if the amps displayed on the controllers is input or output is the most important one. I think that depends on the manufacturer.

[jgrebe]

Originally Posted by noelex 77

But input current is always less than output current (unless you have one of the extremely rare controllers that can boost voltage).

The OP is reporting the solar controller is indicating a substantially higher current than the battery monitor. This shows an error or a fault. If the controller was reporting the input current, the error or fault would be more, not less substantial.

Nolex, good point, I just saw the difference in amps, which is normal, and did not consider the direction of the change. Good catch

[nilespf]

Originally Posted by Perdiem

"If the controller is outputting 105 Amps, and the battery is accepting 75, the other 30 amps have to be going somewhere, or there is a reporting error."

I thought I understood this - but maybe I don't!

We have 3 x 100 watt panels going through a Victron 50 amp smart controller. In full sunshine I get ~16 amps on the battery side of the controller and if the batteries are down it all shows up on the battery monitor.

If the batteries are charged or nearly charged I might only get 3 or 4 amps on the battery monitor. Then if my 8 amp freezer cycles on, I still get the 3 or 4 amps going into the batteries but the 8 amps appears to be picked up by the solar panels.

I thought of it this way. If I go down to the boat and unplug the shore power (batteries have been on float for days) and then leave the boathouse and go out in the sun the panels will be outputting 16 amps but there's no way the batteries will accept it.

Perdiem, Your correct the controller supplies everything the batteries would have supplied because the controller is mandated to keep the buss at a specific value. If the controller is reporting 16A of panel current @ 18V that means some 288W of power (less of course the efficiency factor) is being supplied to the output buss by the controller. If the buss is at a float of 14V that means the current will be about 20.5A Clearly most everything you have is turned on. Just to be clear the only correlation between reported panel input current/voltage and output current/voltage is power. The controller cares about mandated voltage. Mandated voltage is where it is at in the charge profile. Output voltage and buss load variation causes the controller to load the panel seeking VxI combinations quite different than corresponding output voltage/currents.