Ignition battery

[Andy]

This thread is intended to continue the discussion of the emergency ignition battery that started in -
http://forum.cubcrafters.com/showthr...Tips-amp-Hints

This battery has a manufacturer's design life of 5 years but the CubCrafters maintenance manual template suggests it should be replaced annually.

https://www.power-sonic.com/wp-conte...ifications.pdf

In four years one of the ignition batteries I replaced annually was indeed bad.

That seems to suggest that this maintenance strategy is not working. How long had that battery been bad before it was replaced? Did the battery voltage during the emergency ignition test show the battery was failing before it was replaced?

I suggest that periodic discharge testing and careful monitoring of the battery voltage during the emergency ignition test is a far better strategy than assuming the battery will be good for at least, but not more than, one year.

My FX-3 maintenance manual requires a 6 monthly discharge test with replacement on condition. I may revise the test interval based on test results.

[ceslaw]

Andy:

Indeed, the faulty battery did indeed give a clue of its imminent demise. During run up when checking its function the voltage would drop to well below 12 volts in about ten seconds. The engine continued to run, but the significant drop in voltage was concerning.

I don't disagree with your thoughts regarding a means of checking function to avoid annual replacement.

[Andy]

Andy:

Indeed, the faulty battery did indeed give a clue of its imminent demise. During run up when checking its function the voltage would drop to well below 12 volts in about ten seconds. The engine continued to run, but the significant drop in voltage was concerning.

I don't disagree with your thoughts regarding a means of checking function to avoid annual replacement.

Yes, the standard emergency ignition test which should be performed before takeoff can be a good indicator of the battery condition as long as the displayed voltage is monitored. Based on the tests I have conducted I think I shall increase the duration of that test. Perhaps 5 seconds is long enough to see if the battery is in really poor condition but maybe 10 seconds would be better.

I looked back though my data logs and tabulated emergency battery voltage for several checks done over the last 6 months. Although the voltages indicate my battery is still good I did realize that there was some variation in how long each test was run.

I ran a ground discharge test but that is not representative of the in-flight engine running discharge. It may still be a useful baseline for comparison with a later ground discharge test. The data for the in-flight test was representative of real use of the emergency ignition system but that test has some risk exposure. It did give me confidence that my battery is good for over 30 minutes if all else goes tango uniform.

I'll post the test data here because it may be of interest. I do not suggest that anyone should perform this test in flight.

I know some people will be asking - why not just change the battery once a year? The answer is simple - there is some risk that a good one year old battery will be replaced by one that won't last a year. That comment is based on over 25 years experience of using AGM batteries as the sole electrical source in sailplanes.

[ceslaw]

Good information Andy. Reassuring to see the battery gave you a full thirty minutes in actual use.

Just curious, how many thirty minute cycles of use followed by recharging would you trust that battery?

[Andy]

Just curious, how many thirty minute cycles of use followed by recharging would you trust that battery?

I don't have enough test data to make a prediction.

I think you would have to badly mismanage an aircraft electrical system failure to actually need the emergency ignition battery. There should be enough capacity in the main battery to run both ignition systems for well over an hour if non essential loads are shed.

I'd be interested to hear from anyone who had to use the emergency ignition battery to cope with an in-flight failure.

[Mark Albery]

I'm soon due my annual replacement but it seems that the PS-1221s or Yuasa NP2-12 are unavailable in the UK.

Does anyone have experience of other alternatives that work with the existing battery cradle?

[Andy]

I'm soon due my annual replacement but it seems that the PS-1221s or Yuasa NP2-12 are unavailable in the UK.

Does anyone have experience of other alternatives that work with the existing battery cradle?

Some US vendors say they have the PS-1221S in stock, some say it is discontinued, and at least one points to a PowerSonic notification (attached) of part number changes.

There are lots of US vendors selling batteries they claim to be equivalent. I think there is as much variation between batteries of the same make and model as there is across the various "no-name" equivalents.

[Andy]

Just curious, how many thirty minute cycles of use followed by recharging would you trust that battery?

Based on the information in the Panasonic SLA technical manual I'd say 6 monthly testing over the 5 year design life would have no insignificant impact on battery life. Periodic discharge testing may actually increase battery capacity. See figure 9 of attached.

[Mark Albery]

Some US vendors say they have the PS-1221S in stock, some say it is discontinued, and at least one points to a PowerSonic notification (attached) of part number changes.

There are lots of US vendors selling batteries they claim to be equivalent. I think there is a much variation between batteries of the same make and model as there is across the various "no-name" equivalents.

It costs over $100 to get one shipped by a US supplier!

I managed to find an equivalent in Germany - Multipower MP2-12SL.

Still not cheap. Maybe worth looking for a more sustainable alternative set-up.

[Andy]

Based on the information in the Panasonic SLA technical manual I'd say 6 monthly testing over the 5 year design life would have no insignificant impact on battery life. Periodic discharge testing may actually increase battery capacity. See figure 9 of attached.

I have new data that makes me revise that opinion. I recently installed a current sensor which displays and logs emergency ignition battery current for both discharge and the subsequent re-charge. I observed a peak charge current of 3.1 amps after a 30 minute discharge test. After 16 minutes of charging the current had dropped to 1.2 A. The maximum allowed changing current for this battery is 0.3 C or 0.6 amps. It is possible that exceeding the 0.3 C charge current limit will shorten the battery life.

I'm experimenting with a simple charge current limiter. Bench tests look encouraging and I'll provide more information if in-airplane tests are satisfactory.