I spent most of the day making up a test rig to load test my fairly new backup Shorai LiFePO4 battery and for comparison, a 6 year old PC680 AGM.
I made up an array of seven 20 watt Halogen bulbs, which gave a measured current draw of around 11 amps which is close to what a 4 cylinder SDS EFI system draws with one pump running, the ECU, coils and injectors at 2500 rpm.
The Shorai is rated at 18 AH and the PC680 at 16AH.
The first test on the Shorai showed it was pretty much done at the 20 minute mark, getting close to the 12.9V threshold (unloaded)- the point where it's not recommended to discharge below for cell longevity.
The old PC680 soldiered on for over 35 minutes before dropping down into the low 10V range under load (low 11V range unloaded).
10 volts is getting low enough to affect the operation of some components. In particular, the surge current capacity to charge the ignition coils and fire the injectors is diminished. The engine will probably still run down to 9 volts in some fashion though and the ECU doesn't sign off until a bit below 7.5V.
The lower floor level of the hangar was at around 8C during the test to make this a tougher scenario so this may have affected the Shorai more than the Odyssey. I couldn't find any info on how temperature affects capacity on the Shorai but it also affects the PC680 to the tune of 20-30% from the 25C rating.
I want to repeat the Shorai test again when I have time but from this first test, if you are relying on a LiFePO4 for backup power in cooler conditions, you may want to select something larger than 18AH, especially if you have a 6 cylinder system where current draw is higher. In truly cold conditions, you may want to consider an AGM battery instead.
I shot some video which I'll publish at some point when I get time.
Typical LiFePO4 discharge curve
Shorai capacity vs. voltage
As far as our EI systems (CPI/ CPI-2) go, they draw far less current that the full EFI/EI systems so they will run much longer on the same size batteries.
As always, be aware that even colder temperatures, say colder than -20C, severely affect the ability of LiFePO4 batteries to deliver high current for long periods. If you're at altitude on a winter day and the battery is in a location where it's seeing ambient temperatures, don't count on it to last very long if the alternator takes a dump. Also, be aware that batteries lose capacity with the number of cycles they experience. Don't rely on an old, cold battery to keep your engine running.
This test was a bit of an eye opener for me but I'm glad I did it in cool conditions. The lesson is clear here- don't rely on battery AH ratings solely, different chemistries have different characteristics.
I made up an array of seven 20 watt Halogen bulbs, which gave a measured current draw of around 11 amps which is close to what a 4 cylinder SDS EFI system draws with one pump running, the ECU, coils and injectors at 2500 rpm.
The Shorai is rated at 18 AH and the PC680 at 16AH.
The first test on the Shorai showed it was pretty much done at the 20 minute mark, getting close to the 12.9V threshold (unloaded)- the point where it's not recommended to discharge below for cell longevity.
The old PC680 soldiered on for over 35 minutes before dropping down into the low 10V range under load (low 11V range unloaded).
10 volts is getting low enough to affect the operation of some components. In particular, the surge current capacity to charge the ignition coils and fire the injectors is diminished. The engine will probably still run down to 9 volts in some fashion though and the ECU doesn't sign off until a bit below 7.5V.
The lower floor level of the hangar was at around 8C during the test to make this a tougher scenario so this may have affected the Shorai more than the Odyssey. I couldn't find any info on how temperature affects capacity on the Shorai but it also affects the PC680 to the tune of 20-30% from the 25C rating.
I want to repeat the Shorai test again when I have time but from this first test, if you are relying on a LiFePO4 for backup power in cooler conditions, you may want to select something larger than 18AH, especially if you have a 6 cylinder system where current draw is higher. In truly cold conditions, you may want to consider an AGM battery instead.
I shot some video which I'll publish at some point when I get time.
Typical LiFePO4 discharge curve
Shorai capacity vs. voltage
As far as our EI systems (CPI/ CPI-2) go, they draw far less current that the full EFI/EI systems so they will run much longer on the same size batteries.
As always, be aware that even colder temperatures, say colder than -20C, severely affect the ability of LiFePO4 batteries to deliver high current for long periods. If you're at altitude on a winter day and the battery is in a location where it's seeing ambient temperatures, don't count on it to last very long if the alternator takes a dump. Also, be aware that batteries lose capacity with the number of cycles they experience. Don't rely on an old, cold battery to keep your engine running.
This test was a bit of an eye opener for me but I'm glad I did it in cool conditions. The lesson is clear here- don't rely on battery AH ratings solely, different chemistries have different characteristics.
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