Controller dead, can I connect solar panel direct?

[Deltasailor]

Originally Posted by bcripps

Thanks everyone. Specifics:
50 watt panel
two 85 amp AGM Trojan batteries
Liveaboard on mooring
Daily draw... a couple of fans, computer charging
Located in the Dominican Republic

New controller is on order but damn, this is the hottest month of the year! Really need my 2 Hella fans. Lost the Outback controller during Irma. No idea why. But just need to put some juice back into the batteries.
Thanks,
Bry

As others have said yes but don't over charge. BUT make sure you disconnect at night as the panel will take power out of the bank.

[zeehag]

solar panels donot remove electricity from batteries.
i keep mine on a nicely installed analog gage measuring each and every amp and volt in and out.
fake news already.
put an gage into your panel so you can constantly monitor your system. then yoiu can become adventurous with it.


ps if your batteries go down low at night it only means they are not charged up. or they are dead. the panels have nothing to do with that.

[Paul Elliott]

Originally Posted by zeehag

solar panels donot remove electricity from batteries.

I agree. The panels I've measured show no significant leakage / reverse current when dark and connected to a battery.

[john61ct]

then the panel's fitted with a blocking diode
https://www.instructables.com/answer...-output-end-o/

[Paul Elliott]

Originally Posted by john61ct

then the panel's fitted with a blocking diode
https://www.instructables.com/answer...-output-end-o/

No blocking diodes on the two 36-cell 100W monocrystalline panels I measured. I opened the junction box on the back of the panels and looked. There were two bypass diodes, but no blocking diode.

I measured the reverse current with 12.5V applied to a completely shaded panel. The current was 15mA, which is IMHO not worth adding the constant voltage loss of a series diode.

Here is my post where I describe the measurements: http://www.cruisersforum.com/forums/...ml#post2414537

Perhaps some other panel types are worse in this respect?

[waterman46]

Short answer. No problem other than you must monitor voltage. Connect direct to batteries, monitor voltage, disconnect when rises to 14.4 volts, reconnect below 12 .5 or whenever you like.

[waterman46]

The concern about overvoltage of sensitive devices is unfounded. The OP said he would connect the panel directly to the battery hopefully with an appropriate fuse or better a breaker switch. If connected to the house bus instead, its bad since then if the battery switch is turned off that could indeed result in overvoltage on house bus.

[noelex 77]

Originally Posted by Paul Elliott

Perhaps some other panel types are worse in this respect?

Panels do vary, but your results are quite typical.
In most cases, even without a controller, a blocking diode will "cost" more power than it "saves".

[ramblinrod]

Originally Posted by Paul Elliott

And monitor the battery voltage in the afternoon. Fans running or not, if your panels are generating more power than you use, you will eventually overcharge the batteries. One time I did the direct connection after my controller failed. At sea there was no way that they would overcharge the batteries; the best they did was to slow the rate of discharge. But when we reached shore I would have to disconnect the panels around Noon before the batteries got too full.

Originally Posted by waterman46

The concern about overvoltage of sensitive devices is unfounded. The OP said he would connect the panel directly to the battery hopefully with an appropriate fuse or better a breaker switch. If connected to the house bus instead, its bad since then if the battery switch is turned off that could indeed result in overvoltage on house bus.

This is incorrect. If a battery is overcharged it is certainly possible for the charge voltage to rise to a level that could damage electronics intolerant of over voltage.

[john61ct]

It would be a rare bank where the charge buss and loads buss had separate isolation switches.

A good design principal I've seen with LFP protective devices, but I believe rarely implemented with lead banks.

[Stu Jackson]

Originally Posted by waterman46

The concern about overvoltage of sensitive devices is unfounded. The OP said he would connect the panel directly to the battery hopefully with an appropriate fuse or better a breaker switch. If connected to the house bus instead, its bad since then if the battery switch is turned off that could indeed result in overvoltage on house bus.

How would that be different? Aren't the two just the other ends of the same "wire?" (i.e., battery post and house bus?

[newhaul]

Originally Posted by Stu Jackson

How would that be different? Aren't the two just the other ends of the same "wire?" (i.e., battery post and house bus?

The house buss can be isolated from the house bank via a switch . So the panels should be direct to the charging buss or vice that direct to the battery wether thru a controller or not is immaterial to the connections.

[john61ct]

Originally Posted by ramblinrod

If a battery is overcharged it is certainly possible for the charge voltage to rise to a level that could damage electronics intolerant of over voltage.

This is true, without the specialized design outlined above.

Basically unless the panel is very small relative to the batt, the human needs to *be* the controller.

Fine in a pinch, but not for day to day

[ramblinrod]

Originally Posted by newhaul

The house buss can be isolated from the house bank via a switch . So the panels should be direct to the charging buss or vice that direct to the battery wether thru a controller or not is immaterial to the connections.

Charging system connections should always be on the battery side of any distribution system battery isolation switch.

[thomm225]

Originally Posted by ramblinrod

This is incorrect. If a battery is overcharged it is certainly possible for the charge voltage to rise to a level that could damage electronics intolerant of over voltage.

As long as they monitor the voltage, it should be OK.

Example, with no load on a sunny day my 100 watt panel (and/or my 20 watt panel) will read about 22.1 volts which is the Voltage at Open Circuit (VOC) for each panel.

When you hook the panel to the battery, the voltage will read around 12.3 - 12.7 depending on how low the battery is.

The voltage will slowly increase from there as the battery charges.

If you disconnect the battery when it gets to around 14.4 volts or so, you should be fine.