Solar wiring question and TriMetric installation advice

[tdf-texas]

Originally Posted by sclifrickson

Edit: Bummer, the manual says voltage range on my RM2554 is 9.5-15V. If I don’t operate it on DC does this matter? We only ever use AC or LP.

I don’t see specs in the Maxxfan 7500K manual.

The control panel for the fridge always uses 12v power so I guess it does matter. Can the control panel take higher voltages?

[John in Santa Cruz]

Originally Posted by paulk

I don't understand this statement. Is there some sort of voltage regulator in the system that I'm not aware of?

nope, sure isn't. charger voltage == battery voltage == DC system voltage.

[Brian B-P]

Originally Posted by rbryan4

Output to appliances or lights should be unaffected by a higher charging voltage to the batteries. They should be getting nominally 12 volts regardless.

Originally Posted by rbryan4

My point is that the battery output (not the solar charge controller or any other device) should remain unaffected by charge input.

That is not true at all. "Input" and "output" suggest something between those points, and there is nothing. It is not as if a battery has a change input terminal and a separate power output terminal.

Originally Posted by paulk

I don't understand this statement. Is there some sort of voltage regulator in the system that I'm not aware of?

No, there is not, or as already stated:

Originally Posted by John in Santa Cruz

nope, sure isn't. charger voltage == battery voltage == DC system voltage.

The battery, the output of both chargers (converter and solar), the wire from the tug, and the distribution panel for all DC loads are all simply connected together.

Originally Posted by rbryan4

Not a voltage regulator per se (WFCO and others have "over voltage protection" in their units but that is likely only for shore power), but power is still being distributed via the 12v bus in the power center, and I have not seen a direct 1 to 1 correlation between input charging voltage and output voltage. I've measured output slightly increase during an absorption cycle, but nowhere near the actual input which my charger provides.

If you see a difference between charger output and any other point, it is due to voltage drop over the wiring between those points, causes by current and resistance. If battery charging current gets to zero and loads are minimal, everything sees the same voltage... whether that is 11 volts of a dead battery or 15+ volts of an aggressive charger.

Originally Posted by rbryan4

Besides, RV components (at least decent ones) are typically designed to accept the higher voltages. I've not had a single 12v component failure in over 3 years, and I routinely charge my dual 6V batteries at over 15 volts during absorption.

Reasonable automotive components intended for nominal 12 volt DC operation do tolerate a wide range of voltages, although none are likely to ever see the "equalization" voltage of RV chargers, because automotive charging systems don't do that. On the other hand, the idea of "decent RV components" is interesting, since most RV components are junk.

[tdf-texas]

Originally Posted by Brian B-P

On the other hand, the idea of "decent RV components" is interesting, since most RV components are junk.

No argument there!

[Brian B-P]

Originally Posted by Brian B-P

If you see a difference between charger output and any other point, it is due to voltage drop over the wiring between those points, causes by current and resistance.

Also, if the voltage at the converter or solar charger output is significantly different from the voltage at the battery terminals, then the battery is not getting charged as intended because the wiring between converter/charger and battery is inadequate.

In the case of the WFCO converter, the converter output is physically connected to the DC distribution panel by a few centimetres of wire, but connected to the battery by a much longer wire. A DC load which is "close" to the panel (in terms of wire resistance divided by current) can easily see a higher voltage than the battery.

[John in Santa Cruz]

except, as the battery gets chaged, the current drops, and the wire voltage drop isn't nearly as big a deal. its all ohms law, V = Ohms * Amps.

[Brian B-P]

Originally Posted by John in Santa Cruz

except, as the battery gets chaged, the current drops, and the wire voltage drop isn't nearly as big a deal. its all ohms law, V = Ohms * Amps.

True, the final state has the battery near the target voltage. But if your charger is changing stages while pushing enough current to see a significantly different voltage at the charger output and at a load, the transition is not happening at the intended battery voltage. In the ideal state that the battery is topped up and voltage drop is minimal, your LED lights and everything else are seeing that unwanted high voltage.

A solution to this is very obvious: run sensing wire to the battery terminals from the charger, separate from the output wires and not carrying any significant current. If the charger controls based on that voltage, drop in the main wires doesn't matter to achieving the desired charging profile. This generally isn't done, because it would slightly increase both charger cost and installation cost. It would make life even worse for voltage-sensitive devices, because voltage at the transition from bulk stage to the absorption stage at the charger (and loads) would be even higher to make the voltage at the battery as high as intended.

[sclifrickson]

Originally Posted by Brian B-P

True, the final state has the battery near the target voltage. But if your charger is changing stages while pushing enough current to see a significantly different voltage at the charger output and at a load, the transition is not happening at the intended battery voltage. In the ideal state that the battery is topped up and voltage drop is minimal, your LED lights and everything else are seeing that unwanted high voltage.

A solution to this is very obvious: run sensing wire to the battery terminals from the charger, separate from the output wires and not carrying any significant current. If the charger controls based on that voltage, drop in the main wires doesn't matter to achieving the desired charging profile. This generally isn't done, because it would slightly increase both charger cost and installation cost. It would make life even worse for voltage-sensitive devices, because voltage at the transition from bulk stage to the absorption stage at the charger (and loads) would be even higher to make the voltage at the battery as high as intended.

I believe this is how Bogart Engineering’s solar controller works when paired with their Trimetric battery monitor, no? Also Victron has a pair that do the same, if I’m not mistaken.

On a side note, I’ve been using a Trimetric for a while now, but just helped my neighbor set up a Victron BMV-712 battery monitor. The Trimetric is a solid bit of equipment, but lacks user friendliness. Once all set up this is a nonissue, in practice, as you can just leave it on the % Full, state-of-charge readout and be done. The Victron, however, has much nicer bells and whistles, and is much more user friendly. If I were doing it over I’d get the Victron.

[Brian B-P]

Originally Posted by sclifrickson

I believe this is how Bogart Engineering’s solar controller works when paired with their Trimetric battery monitor, no? Also Victron has a pair that do the same, if I’m not mistaken.

Possibly; both of these companies are way ahead of the level of sophistication of most RV equipment. But it's important not to confuse voltage sensing with the shunt used for current measurement.

Bogart's SC-2030 solar charger connects to the Trimetric with a communications cable, so that net battery charging current information is available. The SC-2030 technical manual says

For accurate battery-voltage control, the TriMetric’s voltage-measurement wire (called “B1” in TriMetric wiring diagram) must be connected directly, or close to the battery’s positive terminal

... which suggests that the system is using this more accurate voltage information from the TriMetric.

[paulk]

Originally Posted by sclifrickson

Also Victron has a pair that do the same, if I’m not mistaken.

Yes, for the Victron Battery Monitor BMV-700 serices, the instructions are to run a separately fused wire to the battery terminal which goes to the monitor alone. The monitor does draw a bit of current, but it's only 4mA. In theory they should know what this current draw is and the wire length, so they could compensate.

[algonquin50]

I always wire from the charge controller directly to batteries with an appropriate fuse. However, if your charge controller is mated to your solar correctly, it won't blow a fuse. I mounted my controller in the outside storage compartment on passenger side with about a foot of 10g wire for each. I'll have to check to see the MPPT controller I use, but I've had it for 10 years. I always assume that any factory installed equipment won't suit my purposes.....so I just install everything myself. I like TriMetric stuff...but a little overkill for me. Let me know if you wanna chat on the phone.