Renogy DC to DC not charging at 14.6 volt

Hi, my 20 amps Renogy DC to DC charger is not charging at 14.6 volt, it is only charging at 13.2 volt. I am charging 2 X 100 amps Lithium Batteries in parrallel in the RV. Dip switch are SW5 OFF, 1234 ON as per instructions. I use 6 gauge wires, my Truck batteries are charging at 14.2 volt. Any solution, thank you.

Sigy said:

Hi, my 20 amps Renogy DC to DC charger is not charging at 14.6 volt, it is only charging at 13.2 volt. I am charging 2 X 100 amps Lithium Batteries in parrallel in the RV. Dip switch are SW5 OFF, 1234 ON as per instructions. I use 6 gauge wires, my Truck batteries are charging at 14.2 volt. Any solution, thank you.

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Test voltage at the DC to DC output. Also what is the SOC of the batteries? Do you have a amp clamp?

13.42 volt at the DC to DC output, 13.32 at hr battery.

SOC is 75%

How many amps?

Sigy said:

13.42 volt at the DC to DC output, 13.32 at hr battery.

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With any charger the absorbtion/ boost voltage is a 'target' that the charger will hopefully reach when the battery is full. Due to low Internal resistance the charge voltage will be around 13.4 for most of the charge cycle, the bulk charge stage.
The graph shows the voltage for one cell, multiply by 4 for a 12v battery.
The 0.10 volt drop you measured between charger and battery is due to cable and connection resistance losses, this is acceptable.
With a 14.6 volt absorbtion voltage it's likely the batteries will enter protection mode due to cell inbalance.
You may need to reduce the charge volts to 14.4 or 14.2, even 14.0 will still charge.

mikefitz said:

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With a 14.6 volt absorbtion voltage it's likely the batteries will enter protection mode due to cell inbalance.
You may need to reduce the charge volts to 14.4 or 14.2, even 14.0 will still charge.

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There does seem to an overzealous attempt by the DC-DC charger manufacturers to push LiFePO4 4S systems to 14.4 - 14.6V and then float.
Certainly in the off grid world most would not be pushing their cells above an equivalent of 14.0V. Some of the manufacturers of LIFePO4 4S packs also recommend charging to 14.6V.
I can't join the dots to work out why 14.4- 14.6V is recommended, other than a legacy of lead acid profiles.

ocular said:

There does seem to an overzealous attempt by the DC-DC charger manufacturers to push LiFePO4 4S systems to 14.4 - 14.6V and then float.
Certainly in the off grid world most would not be pushing their cells above an equivalent of 14.0V. Some of the manufacturers of LIFePO4 4S packs also recommend charging to 14.6V.
I can't join the dots to work out why 14.4- 14.6V is recommended, other than a legacy of lead acid profiles.

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My best guess at this point is marketing. If one company decides to suggest more realistic voltages, such as 13.9-14.2V, they will have an uphill battle to convince why they're not wrong since every other company out there suggests 14.4-14.6V. If they played their cards right and stood solid on their claim (with proof), they might be able to swing customers to them, but if they make a wrong move (such as point blame to another company or otherwise get defensive) they will dig their own grave.

To that end, in my currently limited knowledge, charging to 14.4-14.6V itself isn't all that bad for LFP cells...it is what is recommended by the LFP engineers, as far as I know. What's bad about it is that unless the cells are extremely well balanced, then the BMS will trigger charge protection before the target voltage is reached. It may not trigger at 14.0v, but might very well trigger at 14.3. So if the target is 14.4V, the BMS will trip every single charge cycle. Unless you have a high-end BMS (most of the off-the-shelf batteries do not), then it will likely be inevitable you will need to replace the BMS, which can be next to impossible in some of the cheapo LFP off-the-shelf batteries.

Of course there are finicky ways to balance an off-the-shelf battery, but these instructions are NOT included in off-the-shelf batteries and it took experts on this forum to help me figure that process out! Not too difficult once you learn, just tedious and time-consuming. Or build your own LFP pack with an above-average BMS like JK or JBD, throw a $20 active balancer on there and it will do it automatically in a few hours or days.