Setting your Trace Auto Gen Start Parameters

[davidbrady]

I've been drydocking for two weeks. The auto start feature of the Trace SW4024's is factory default set as follows:

24hr: 24.6V
2hr: 23.6V
15min: 22.6V

The generator will start if the battery voltage is below any of the above three parameters for a time greater than that above. The problem is these values will allow your batteries to discharge far below 50% before the generator starts.

Here are the SOC vs OCV (open circuit voltage) values for the Lifeline AGM:
60%: 24.6 VDC --- Trace 24hr genny start timer begins
50%: 24.36
40%: 24.12
30%: 23.88
20%: 23.64 --- Trace 2hr genny start timer begins
10%: 23.4
0%: <23.16
-- Trace 15min genny start timer begins

The problem I've been seeing is the batteries are being discharged to well below 50% and as low as 20% before the generator is auto started. Turns out the default factory generator settings aren't suitable.

If the discharge rate is between 10 and 20 DC amps, which is our expected load when not running air conditioners, then in my case with an 800 A-hr battery bank, the batteries will be discharged to 50% in 20 to 40 hours. This doesn't line up well with the factory auto genny start parameters. Say we're in the middle at an average 15A DC draw. The 24hr timer will begin at 60% SOC which will be after 21 hours. When the timer expires 24 hours later my battery bank is well below a 20% SOC which is terrible for the longevity of AGM's. What happens in my case is that when the 24 hr timer is around the 20 hour point the 2 hour timer kicks in and the batteries start at a SOC slightly below 20%, which is still bad.

The matter is even worse if you're using a battery which isn't quite as high performance as a Lifeline such as an East Penn. These batteries all have SOC vs OCV values which are a good 0.1V above the Lifelines which means the default Trace auto generator start timer parameters will leave these batteries even further discharged.

The answer is to configure you generator start timers to start at higher battery voltages. I view the 24hr timer as a no load genny start parameter allowing the batteries to be topped up every now and then during periods of non use. The 2hr timer is the one I consider to be the most effective for our typical use case. The 15min timer is for cases of heavy draw, air conditioners for example, where you want the generator to start almost immediately. I have my auto gennerator start configured as follows:

24hr: 25.0V
2hr: 24.6V
15min: 23.6V

The important change is bumping up the 2hr voltage to the battery's 50% state of charge voltage level.