Trace SW 4024 Charging Mystery

[TC McClure]

One would think that after 40 years off grid, I would have seen everything. But.......I have inverted for 28 years with a Trace SW 4024 inverter. Recently, a lightning strike near my PV system rendered my old trusty Trace unable to charge. (Inverter to 120 V was OK)
I decided to purchase another used Trace SW 4024 because I was familiar with it. The replacement works great except during charging from my P9500 df ONAN/CUMMINGS generator. Within 30 seconds of "charging" the Trace's DC Volts meter reads 28.0 V. My Outback 80 controller also reads 28 V and multi tester on my series lead acid batteries reads 28 V on all 5 series. When I turn off the generator, the battery voltage drops slowly back down. The final voltage is dependent on the voltage present when charging started.
My old Trace charged the batteries as expected (a slow climb) for 28 years.
Your thoughts are appreciated in advance.

 

[sunshine_eggo]

Have you confirmed these readings with a separate voltmeter?

Since you've been swapping hardware out, see link #2 in my signature - check every single connection in the path.

If everything checks out, it may be a battery issue. As FLA batteries "wear," their internal resistance goes up, so you'll hit absorption sooner than before.

 

[MisterSandals]

My old Trace charged the batteries as expected (a slow climb) for 28 years.

Are your SW 4024's setup to charge at the same rate and voltage?

Same firmware? Schneider has varying amounts of bugs/glitches in their different firmware (its sad).

 

[sunshine_eggo]

Are your SW 4024's setup to charge at the same rate and voltage?

Same firmware? Schneider has varying amounts of bugs/glitches in their different firmware (its sad).

I'm reading this as a single 90's vintage TRACE SW4024, not Schneider. There is brand confusion due to the SW4024 model number being used by both.

Trace was bought by Xantrex in 1999.

 

[MisterSandals]

Trace was bought by Xantrex in 1999.

And Xantrex purchased by Schneider in 2008

(behind paywall but first few sentences can be read)

https://www.wsj.com/articles/SB121729289562691841

 

[TC McClure]

Thanks. Both the original and the replacement are mid-nineties TRACE. I will clean and polish the connections on the FLAs but it's hard to imagine that connections would cause 28V from 23V in 30 seconds. While I waited for the replacement to arrive, I purchased a 25Amp, 24 Volt battery charger. The voltage climbs slowly and steadily when charging on the same battery bank with the same connections.

 

[sunshine_eggo]

Thanks. Both the original and the replacement are mid-nineties TRACE. I will clean and polish the connections on the FLAs but it's hard to imagine that connections would cause 28V from 23V in 30 seconds.

With a loose or high resistance connection ANYWHERE in the circuit, it's not hard to imagine at all. That's also why it's important to confirm any readings with a separate meter.

While I waited for the replacement to arrive, I purchased a 25Amp, 24 Volt battery charger. The voltage climbs slowly and steadily when charging on the same battery bank with the same connections.

So you connect the charger at the INVERTER battery terminals?

 

[RCinFLA]

On the replacement unit you likely did not setup the charging current rate. It defaults to maximum current, about 100 amps to battery. Trace charging amperage is based on AC input current. For a 24v version it is roughly 120vac/25vdc or 4.8x scaling factor. 10 amps AC charging setting equals about 48 amps to 25v battery.

Aside, on the busted Trace SW inverter check if applying the source AC to other AC input, ACin1 or AC2, will make it connect to AC input and work normally again.

There are two small 120vac to 12.6vac voltage sense transformers, T4 and T8 on PCB, to measure the AC input voltage on each of the AC1 and AC2 inputs. The 12.6vac output of transformer is actually fed to control board and measured to represent the AC input voltage, just scaled down in voltage to be safer for control board.

Primary 120vac side winding resistance of transformer is about 1200 ohms. Check it with ohm meter placed across respective ACin to neutral.

The small transformers are located on AC/transfer relay board on the left side. The small transformers 120vac primary side windings are hair fine wire and can easily be popped by an AC surge from a neighborhood lightning strike. It only pops the transformer on the ACin port that was active during the lightning strike, others input remains undamaged.

If AC input voltage sense transformer is open, the inverter thinks there is no AC input applied on that ACin port and will not attempt to connect to it.

'T4' and 'T8' in below diagram.

 

[TC McClure]

Thanks for the notes. Sunshine_Eggo nailed it! I had neglected to properly service the batteries and clean the connections. I cleaned and polished the connections. I replaced a couple of connection leads, replaced two batteries (one actually had a DEAD cell), filled all cells and equalized the batteries for a couple of hours. The battery bank returned to normal, holding power through the night from 25V down to 23V by morning.

But the Trace still charged the batteries quicker than I thought it should. I scaled the Max Charge Amps back to 10A as recommended by RCinFLA and the climb was slower and acceptable. I turned the generator off at 27.5V and it settled back to 25V.

To RCinFLA:Thanks for the schematic. I moved the "in" wires to AC1 in without success and that led to my purchasing a replacement. Actually, I'm glad to have a stand by inverter "just in case." If the "hair fine wires" were popped, who could fix something like that? I'm good with a chainsaw but taking the face off of the TRACE fills me with fear.

Anyway, thanks guys for reminding me of what I should have known initially.