question

kaz-oz avatar image

Feature request PLEASE ALLOW Absorption time less than 1 hour

DC DC 30a charging lithium, I want to set less than 1 hour Absorption time, so I can keep my batteries ~70-90% max soc then float. I use it in my car so it's rare that I run it more than 1 hour at a time. I see this is a big issue with victron range. Love the product, just this one issue will force me to look elsewhere.

VRMsoftware
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
Alexandra avatar image
Alexandra answered ·

@Kaz_oz

Dc to dc chargers dont know soc.

Since bulk and absorption are the same voltage and the only difference between the two is the amp draw of the battery, not sure how this will help you?

A tweak is setting lower target voltage of you arent aiming at full.

You dont mention your specific product so cant help you more, except to say you can have bmv to switch a relay to disconnect and reconnect the battery at certain soc if that is what you want. So there are ways, you just need to get creative.

2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

kaz-oz avatar image
kaz-oz answered ·

Thankyou for the reply.

In victron connect I can create a profile with 1 minute absorb time and save it, but when i select this profile it will change it to 1 hour. Surely this is a software bug.


My device is DC DC 30a Non-isolated Charger. I have a coulomb meter display that shows SOC, voltage, current. 120ah LIFEPO4 battery. Smart alternator.


Current options are:

1- Set to 14.1v charge, 13.4v float. Unit will bulk to ~90%, absorb to ~100% SOC then float. Purely at the mercy of "adaptive absorbtion", multiple car starts will restart this and it can quite easily overcharge my battery.

2- Set to power supply mode 13.6v. Unit will bulk to ~40%, then current will taper down to a slow absorb charge to 100%. This is not useful in practice, it is low SOC when i need it.

Theres not much inbetween that I can do other than change settings every time i want it to do something different.


What I want is to Bulk 14.1v (30a) gets it to ~90%, 1 minute absorb, then float 13.4v. So then if I do a 5 hour drive it will not overcharge, and it also gives me fastest charge. Lithium doesnt really need an absorbtion time due to the low internal resistance. But lifepo4 I still need to set a higher than float voltage to get it to charge at max rate.


I have a programmable voltage sensitive relay that I can use to switch the charger on and off, but I want the float feature. Am I really going to have to buy a second unit set to float voltage?

4 comments
2 |3000

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

Depending on capacity, lifepo4 does need absorption since voltage does not indicate SOC on them. Have experimented quite a bit on this matter.

Also with bms it is (other than failure there) it is impossible to overcharge a lithium.

Adaptive charging is based on start voltage etc so even there it will adjust itself based on where it starts. (again have experimented here)

Most battery manufacturers want the absorption for cell balancing as well, so it is more than just a target voltage. In absorption is it not thumping 30A in anyway it is tailing it off. Once the battery has said enough then it drops to float.
Yes but lifepo4 prefers 50% SOC so id rather keep it to 80-90%.

On the contrary, with a 30a supply to my 120ah low resistance lifepo4, I find when it is flat it will gradually increase voltage from 12.5 to 14. If it was a smaller battery or larger current then it would hit the absorption phase earlier.

Look at tesla , they charge their lifepo4 to 80-90% by default.

I can fully charge it and then float it, it will be pushing on 100%, I don't want this.

Tesla has completely different chemistry to the batteries you are using.

The manufacturer of your battery will be hovering charge between two points in the cell useable voltage range anyway, so the 100% you are charging to is not actually 100% of the full cell capacity.

Charge the battery as the manufacturer recommends.