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Old 01-30-2024, 05:51 PM   #11
larsdennert
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The 120V converter will also need to be able to supply 14.6V to charge Li. Some WFCO ones have a sense circuit. Most tow vehicles isolate the Bargman charge lead when the truck is not running.
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Old 01-31-2024, 04:13 PM   #12
rickst29
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Default You DON'T want "14.6V" DC charge voltage for Lithium.

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Originally Posted by larsdennert View Post
The 120V converter will also need to be able to supply 14.6V to charge Li. Some WFCO ones have a sense circuit. Most tow vehicles isolate the Bargman charge lead when the truck is not running.
Charging Lithium "TM" batteries from the 120-VAC converter board has been addressed in some other Threads, I hate to see that separate topic introduced to this "charging from the tow vehicle alternator" discussion.

Some "Lithium" cell types use other chemistry, allowing them to handle higher voltage. But Lithium batteries in TM Trailers should be built using "lithium-ferro-phosphate" cells, which are less likely to catch fire and generally provide longer lifespan. Each "12v-compatible" battery pack contains 4 cells in series, and 14.6 volts of charging voltage subjects those cells to an average of 3.65 volts each.

That is the absolute maximum voltage to which a single cell should EVER be charged. Such a high voltage should be reached only once, for capacity testing (and I generally recommend not to bother with that, even one time).

The battery BMS should be be programmed to prevent current from reaching the batter pack when the sum of voltages (n the battery) has reached more than about 13.45 Volts, roughly 96% charged.

(1) It not useful to apply 14.6 volts into the "12 Volt DC" at all times (when the 120-VAC cord has been plugged in). It would be more efficient and better for the Converter's electronics to shut down the Conversion circuits, only re-activating them when voltage testing on the DC side (voltage supplied by the battery) has somewhat lower than 13.45 volts.
- - -
For driving current into "12v" LFP battery packs, virtually nothing is accomplished by attempting to supply more than 14.2 volts anyway. (An "attempt" to reach just 14.0 volts will likely utilize all of the current which a low-powered charger can supply during "bulk" charging, before reaching that voltage, because the internal resistance of these battery cells is very low).

I have my own Converter set to see my Lithium batteries as "AGM/GEL", and that is probably the best battery-type setting to use with non-programmable controllers. To the extent that forcing a non-programmable Converter to resume "bulk" mode" when the battery is lower than I'd like, I have a programmable a Solar controller to take care of the last few % of capacity (ending no higher than 97% full, NOT near 100% full.)

With my older model "WildKat", a modified non-programmable PD controller, I'm not sure that the charge wizard push-button "mode switch" can actually push it past some non-programmable and hidden parameter, "minimum voltage at which to resume bulk charging from float". Some times it seems to work, other times it doesn't.

Some Victron Converters are are programmable, but they tend to be either lower-power or very expensive.
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