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I notice when the charger is in Bulk charge phase, the voltage at the charger generally reads around 14v yet at the battery, the voltage reads around 13.5v, then at absorption stage the battery voltage increases to around 14.2v.
Is this normal behavior or should the voltage at the battery always correspond with the voltage at the charger whatever the charging phase?
note: paired with Renogy 100amp LifePO4
Voltage should be the same at the battery and charger. Could be poor connection somewhere.
The battery should show an creased voltage as it charges, and a constant voltage during absorption.
Are you measuring the battery voltage, or is the battery reporting it? If it's the battery it would be helpful to check with a meter.
Interestingly, voltage test at battery = 13.64v whilst BMV712 (with supplied wiring and connectors) reads 13.36v
This is after I replaced the positive and negative cables from the battery charger to the battery, using hydraulic press for crimped terminal rings to 10AWG cable over 15ft (both ways).
(I think this is a bit under-spec'd but was all I had on the boat. Will replace with 6AWG and use a length of 20ft of total length of both cables.
+ Battery Charger to + Battery = 0.22
- Battery Charger to - Battery = 0.22
Check to see what the expected voltage drop is for the wire gauge and length you have between the charger and the battery. That may account for the lower voltage you're seeing at the battery.
https://www.youtube.com/watch?v=0xOvINH4tKs
Based on using his calculator it appears that its within 3 or 3.5% voltage drop. It'll be interesting to see the difference with bigger cabling.
What confuses me on the voltage drop is that as soon as it hits Absorbsion I get 14.2 at both ends, so it feels like I get voltage drop during bulk charging and no drop at Absorbsion. Lots to learn! Thank you for commenting.
Your voltage drop looks normal to me, especially since you're using smaller 10 AWG wire.
Voltage drop (resistance) is directly proportional to amperage so we'll get more voltage drop at higher amps. When the charger switches to absorption phase, it charges at a constant voltage with decreasing amperage until the battery reaches that absorption voltage. That means voltage drop will also decrease. It is interesting, though, that your voltage is exactly the same at the charger and at the battery during the absorption phase. I can see how they might be exactly the same at the end of the absorption phase, but during is interesting.
Your total circuit length is 15x2=30ft (~10 meters), so the recommend wire gauge is 16mm2 (~6 AWG).
While 10 AWG wire's ampacity for 30ft is indeed 30 amps, it does so with greater voltage drop (listed under the 10% non-critical voltage drop row).
FYI, this charger is capable of outputting 40 amps under ideal conditions.
