Transfer switch LV cutoff settings and voltage drop under load

[furkidmom]

Hi, new here. We have a 24v DIY solar setup to power our pond pump. We have four 12V, 200Ah AGM batteries wire in serial/parallel to make 24v system w/a 3000w inverter. There is a transfer switch so that when the battery power drops, it transfers to 120V household current. The idea was run the pump on solar during day, and to have a few hours of battery power in the evening, when peak use rates hit. We recently discovered that when the load is transferred to the batteries, the voltage drops so much that it only runs on batteries for a few minutes, then switches back to 120V, then the battery voltage runs back up, and a few minutes later it transfers back to batteries. It seems that this is happening in AM/PM when solar production is low. During the day, it appears to be running on batteries. But, once the sun goes down we are getting no battery operation, even though the batteries are fully charged. The LV transfer was set to 23.5. The batteries are Apex 12-200. spec sheet has float 13.6-13.8, Equalization 14.6-14.8 There is no LV cutoff on spec sheet. My question is whether this is normal, or is there something wrong with our setup that is causing the battery voltage to drop excessively under load. Is it OK to set the LV switching to 22.5V so that it is below the point that the load is drawing down, so it isn't switching back and forth constantly. Yes, we are novices at this... so appreciate gentle constructive input.... Thanks. -cj-

 

[Boondock Saint]

I see you're using AGM and not true deep cycle batteries. While AGM will let you pull a load longer and deeper than standard SLA is still isn't a marine deep cycle battery.

Initially I'm curious as to the current draw from the pump at 120V? Do you know what this is?

Are you able to measure the current draw of the pump at 120v? And subsequently inline on the 24v side going to the inverter?

If you set the LV down a notch, it will probably buy you more time, but will still end up duty cycling back and forth between the line voltage.

 

[furkidmom]

Thanks so much for the reply. I have a Kill-a-Watt meter. Plugged directly into a 120 outlet, not on the solar system, It says 2.95 Amp, 115.5 v, 303W, and I think it's 59.9 Hz When plugged into the outlet fed by the inverter, the numbers are almost identical.. 2.92/119/302/60. I appreciate any help or insight you can offer.

I see you're using AGM and not true deep cycle batteries. While AGM will let you pull a load longer and deeper than standard SLA is still isn't a marine deep cycle battery.

Initially I'm curious as to the current draw from the pump at 120V? Do you know what this is?

Are you able to measure the current draw of the pump at 120v? And subsequently inline on the 24v side going to the inverter?

If you set the LV down a notch, it will probably buy you more time, but will still end up duty cycling back and forth between the line voltage.

 

[Diysolar123]

a few things to check...
1) wiring sized to small could make the current drain an issue; maybe its an excessive voltage drop on cables that are to small
2)pumps (well, any motor) have a "surge" current demand that you may not be seeing. Only a meter with an "inrush current mode" can measure this. Depending on your motor the real current could many times what the "running" current is.
3)verify what the capacity of each battery is, independently!! You "may" have a weak battery; battery voltage is VERY different than battery capacity. You are runing a 2S2P config so you could just use 2batteries in series (2S1P) and see if it runs ok, then try the other two as a seperate pack. You can use this to try and see where the problem may be. That "all" batteries have a problem while possible is unlikely. DO not rely on "voltage", you need to either check actual capacity or, get a cheap battery load tester and try that.
4) if you can get a battery internal resistance meter that will give you a quick view of the health of the battery
5)double check your cables/connections are tight; a poor connection can cause what looks like transient outages.

 

[Boondock Saint]

a few things to check...

1) wiring sized too small could make the current drain an issue; maybe its an excessive voltage drop on cables that are to small

2) pumps (well, any motor) have a "surge" current demand that you may not be seeing. Only a meter with an "inrush current mode" can measure this. Depending on your motor the real current could many times what the "running" current is.

3) verify what the capacity of each battery is, independently!! You "may" have a weak battery; battery voltage is VERY different than battery capacity. You are running a 2S2P config so you could just use 2batteries in series (2S1P) and see if it runs ok, then try the other two as a separate pack. You can use this to try and see where the problem may be. That "all" batteries have a problem while possible is unlikely. DO not rely on "voltage", you need to either check actual capacity or, get a cheap battery load tester and try that.

4) if you can get a battery internal resistance meter that will give you a quick view of the health of the battery

5) double check your cables/connections are tight (and clean) ; a poor connection can cause what looks like transient outages.

All of DIY suggestions.

Admittedly that's not much of a load.

If it were me, I'd switch the load to AC perm and let the batts fully charge for a day, straight up fully charge.

Tell us more about your solar panels and SCC, what are their ratings? It might be that at the end of the day they just can't charge rhe 2 AGM sufficiently ro hold enough juice ro run the distance.

At dusk use a standard volt meter and read/ watch the voltage on the batts.

With a starting voltage reading on the batteries, and a start time I would measure the gradual voltage drop on the batteries while the pump runs AND until the LV xfer switch over.

If the voltage of the 2 batts in parallel drop quickly then there's a problem with the supply, cabling, connectivity or the batteries are just under rated for the task and you need marine or lithium.

 

[furkidmom]

OK, I'll probably need hubby to chime in here at some point to help with specifics.

1. Five Hanwa Q-Peak L-G4.2 370 Watt Solar panels connected to a 60A Y-Solar Charge controller (60A MPPT Solar Charge Controller 48V 36V 24V 12V Auto, 60 amp Positive Ground Charge Regulator, Max 150VDC Input with Backlight LCD Display for Lead-Acid Sealed Gel AGM Flooded Lithium Battery)
2. single panel, same model to a 20A epever Charge controller. (EPEVER MPPT Charge Controller 20A Tracer2210AN + Remote Meter MT50 + RTS 12V/24V Auto with LCD Display for Solar Power Battery Charging Regulator System (20A + MT50+RTS
3. The inverter is a Reliable RBP-3000S-LED 3000w Pure Sine Wave Solar Power Inverter 24v 120v 60hz With LED Display (Black)
4. Outlets for pond equipment are hard wired to the Transfer switch, that is a short run, maybe 6'.
5. I think the run from the panels to the batteries/inverter etc. is about 50'
6. The wiring from panels to charge controllers is. TEMCo 100' Red + 100' Black 10 AWG/Gauge Solar Panel Extension Cable

It got set up this way because one of the panels they sent us was bad, and they sent us a replacement. Then my husband figured out what was wrong with the original panel, got it working, and we added it to the system. He will have to chime in on the parallel, serial set up of the panels, He figured out that part. -C-