Unhooking battery from pwm SCC

[mhbell]

When I hooked up my renogy 100 watt starter kit the instructions caustioned not to hook up the solar panels to the 30 amp PWM SCC first. The instructions stated that the battery / batteries had to be hooked first to the SCC befor hooking up the solar panels. Failure to do so would cause damage to the SCC. My question is I want to install a disconnect switch in the positive lead from the battery. What happens if I disconnect the battery/ batteries from the SCC without unhooking the solar panels.
Any help or suggestion would be appreciated.
Mel

 

[snoobler]

You violate the recommendation and risk damaging the unit.

Install a disconnect on the panel to SCC side too and cut it first.

 

[mhbell]

That really doesn't make sense to me. What if you unhook the battery for maintenance or it goes dead? Guess I will put the switch on the panel positive wire. The only reason I want a switch was to be able to cut the solar out of the system when on shore power. I was told that it would not hurt to hook up shore power and have the solar on at the same time. Just not sure.
Mel

 

[Byrogie]

That really doesn't make sense to me. What if you unhook the battery for maintenance or it goes dead? Guess I will put the switch on the panel positive wire. The only reason I want a switch was to be able to cut the solar out of the system when on shore power. I was told that it would not hurt to hook up shore power and have the solar on at the same time. Just not sure.
Mel

SCC require battery hook up first because it is the power source for the controller. Somebody smarter than me can explain why. You should have fused switch or breaker between panels and controller as well as between controller and batteries. Does not hurt to have solar and shore power on at the same time.

 

[mhbell]

Thank You, that is what I wanted to know. I have PV fused and battery fused. No switches yet. I will contact renogy for clarification. I can see where when you first hook up the controller the battery would have to be hooked up first, but once the battery type all all of the settings are done, I would think that you could safely unhook the battery power from the controller. The renogy PWM 30 amp is supposed to have certain protections built in. perhaps someone who knows whether it is safe to unhook the battery from the controller without unhooking the panels will chime in to this post.
Mel

 

[chrisski]

Read a post can that is something like "can you fry your SCC by disconnecting it." Most said they did it and it did not matter. One guy said he fried a PWM controller when not having a battery hooked up. Aside from that one incident, it certainly violates the owners manual and now the company is not liable for any damage, and with my build and others the SCC is a small part of the cost, especially if whatever it causes cascades down the system.

I think a battery switch is a very good thing to have. If you are simply installing it, it can certainly be done at night when the panels are producing no power.

One of the few things I'm waiting on before a hit the "on Button" for my 1KW RV build is installing my battery on off switch.

 

[gnubie]

The can I fry it mostly surrounded the way MPPT controller's work and the potential for a high voltage spike if the load suddenly goes away. That's not really an issue with PWM since for what the industry calls a PWM charger there isn't any output inductor. I can think of a few ways a PWM controller might have functional problems but failing outright would be surprising to me.

 

[Zil]

I have a MorningStar pwm. I use a Blue Sea DPST battery switch to disconnect the battery and the panels at one turn of the switch. 4 years with no problem. https://www.bluesea.com/products/6010/m-Series_Mini_Dual_Circuit_Battery_Switch_-_Red

 

[mhbell]

I have a MorningStar pwm. I use a Blue Sea DPST battery switch to disconnect the battery and the panels at one turn of the switch. 4 years with no problem. https://www.bluesea.com/products/6010/m-Series_Mini_Dual_Circuit_Battery_Switch_-_Red

That sounds like something I will have to get. Thanks for the info.
Mel

 

[grizzzman]

I have also have a Morningstar and a trimetric SC2030 and a grape solar SCC all PWM that deal with battery just fine. Its the real cheap solar controllers that go "poof"

 

[Hedges]

The can I fry it mostly surrounded the way MPPT controller's work and the potential for a high voltage spike if the load suddenly goes away. That's not really an issue with PWM since for what the industry calls a PWM charger there isn't any output inductor. I can think of a few ways a PWM controller might have functional problems but failing outright would be surprising to me.

The main one I can think of is if specified maximum PV voltage is higher for higher voltage battery (48V), lower for lower voltage battery (12V)
That would indicate the transistor has voltage and/or wattage limits. A 50V transistor might be able to switch 80V panel onto a battery discharged to 40V or fully charged at 60V. For 12V battery, 60 Voc would reach transistor absolute max, 50 Voc could be OK. But even 50 Voc would be too much into zero volts for disconnected battery. (About 25 Voc, 17 Vmp from panel is closer to what PWM for 12V battery wants.)

If you disconnected battery and inverter or other load pulled it to zero volts ... or if battery was disconnected but inverter with its input caps were present at zero volts and you connected PV first ... then the transistor sees full PV panel Voc.

An MPPT could have an under-rated transistor like that. For a "buck" (voltage reduction" switcher, transistor is connected between PV panel and battery positive, just like PWM. Difference is, there is an inductor in series and a diode to let inductor keep pushing current into battery even during the period when PV is momentarily disconnected.

Yes, the inductor would kick out high voltage if battery disconnected. Transistor doesn't see that, but other electronics does. Depends on how robust the circuitry to isolate or clamp that spike.

 

[gnubie]

It's a valid point but at least from the few cheap blue PWM controller's I've taken apart the labelling on the transistors put them at higher failure voltage but that assumes they aren't fakes or relabels.

 

[ghostwriter66]

Thank You, that is what I wanted to know. I have PV fused and battery fused. No switches yet. I will contact renogy for clarification. I can see where when you first hook up the controller the battery would have to be hooked up first, but once the battery type all all of the settings are done, I would think that you could safely unhook the battery power from the controller. The renogy PWM 30 amp is supposed to have certain protections built in. perhaps someone who knows whether it is safe to unhook the battery from the controller without unhooking the panels will chime in to this post.
Mel

YOU MUST connect the batteries FIRST and disconnect the batteries last ... Going to say that there are DOZENs of folks on here that can attest to factory smoke being released otherwise

 

[Hedges]

And so ... if you have a BMS, do you wire it's "disconnect" signal to a relay which simultaneously disconnects the PV?
If inverter fuse/breaker trips, and SCC is connected after that, do you buy another SCC?
Should we take battery voltage at SCC and feed it to the coil of a relay for the PV?

If inductive kick is the problem, don't see how simultaneous operation would fix the problem.
A suitably sized transient voltage suppressor would be needed.

Seems like you want a way for protection devices to work without killing hardware.
And you want human-operated switches interlocked so they don't get operated in the wrong order.
Installer you can count on to do it correctly once, when commissioning the system.

 

[Zil]

YOU MUST connect the batteries FIRST and disconnect the batteries last ... Going to say that there are DOZENs of folks on here that can attest to factory smoke being released otherwise

Not true with my PWM MorningStar CC. I have proved by doing. I can disconnect both battery and panels at the same time. I can re-connect them at the same time as well. I have been doing this 4 years with no problem. I did connect the battery first when I initially installed the system. That allowed the CC to recognize the battery.
I have set the custom settings so the CC disconnects the panels when the LFP battery reaches voltage. Then reconnects when voltage falls.

 

[John Frum]

YOU MUST connect the batteries FIRST and disconnect the batteries last ... Going to say that there are DOZENs of folks on here that can attest to factory smoke being released otherwise

Have you seen it personally?
Anyone else witnessed this?

 

[turbineinfo]

Just to share, I have a small 12 volt system…Xantrex 40 amp pmw controller, 3 Kyosera 135GX-LPU 12 volt pannels (wired in parallel) . On the load side of the CC, I have a high grade manual switch where i can redirect the output current 1) to a small (6 golf cart battery) array; 2) to a modified set of car jumper cables for charging individual 12 volt lead-acid batteries; 3) to nothing at all (e.g. off…no battery connection at all).
I have never disconnected my PV panels when switching the CC output between various 12 volt batteries. I have even set the output switch to off for days..meaning no battery connection while the CC is fully connected to the PV array. Ive been doing this for about 10 years and never had a problem.

 

[Hedges]

PWM is just a transistor switch which shorts PV panels to battery, or not. So unsurprising it has no objection to you flipping a switch which connects its output to battery, or not.

 

[rhino]

Just checked the Victron SmartSolar manual and has this in it: (which is MPPT but thought it interesting none-the-less)

We do not recommend to use the solar charger as a power supply, that is without batteries connected.
Operation as a power supply will not damage the solar charger, but it is not guaranteed that the solar charger is able to run all types of loads. Some type of loads might run, others might not. Especially at low load power, the solar charger is too slow to keep the voltage constant. As such, we do not provide support in these kind of situations.

 

[chrisski]

Just checked the Victron SmartSolar manual and has this in it: (which is MPPT but thought it interesting none-the-less)

I’ve accidentally used the SCC with the battery off and it will run normal DC loads and let the inverter idle, but anything other than small loads will cause the inverter to fault out.

I never run without a battery on purpose but have forgotten.