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thisbigroadtrip avatar image
thisbigroadtrip asked

Tail Current Questions

HI.

I just installed my MPPT 100/50 and had a couple of questions about tail current.

1.
If the Tail Current dictates when the batteries need to flip over into Float. Why is there an Adaptive Charge setting at all?
I think Adaptive Charge sets the time for Absorb based on a multiplier of the morning voltage of the batteries and Max Absorb Time.
Turn Adaptive off and just the Max Absorb Time is used.
In both instances, Tail Current (if switched on) would flick the batteries into Float mode. But Adaptive mode could time out before that tail current is hit,. Wouldn't that mean that the Absorb time was too short?
With Tail Current available to dictate when the batteries are full, why would you need an Adaptive mode at all?

2.
How does the Tail Current work if the sun goes in and the current drops. Does it just switch to Float prematurely?

BMV Battery Monitor
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2 Answers
pwfarnell avatar image
pwfarnell answered ·

The controller only flips to float if the voltage is at absorb voltage AND the current falls below the tail current. This stops it dropping to float due to cloud.

The use of tail current can be misled if there are loads on line when the battery is being used, say you have a 5amp load and have set the tail current to 4amp, it will never reach it using the current measurement within the controller. Therefore you should always have a maximum absorption time set. But this means that if you have fixed the absorption time and have lightly discharged your batteries, you could be giving them too long on absorb.

However, if you have a BMV battery monitor and GX device then you can set up DVCC and SCS so the actual charge current into the battery is used and the effect of loads is ignored. In this case you are able to use a fixed absorption time knowing that the tail current will quickly go to float on lightly discharged batteries and not overcharge them.

The adaptive charging is there to cater for simple sets ups using an MPPT controller only and has loads drawn whilst the solar is working to avoid overcharging.

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Vance Mitchell avatar image
Vance Mitchell answered ·

Adaptive_charging_how_it_works

This might help explain some of it and hopefully someone with more knowledge on the subject can come in and answer the rest.

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