Balance with asymmetric battery size?

[TheB1gG]

Hi,
I have two batteries: a Venus D with 15 kWh and a Venus E with 5 kWh.Currently, I use the CT003 emulation with active control and min_efficient_power, which works great. Thank you for this great piece of software.

My problem is that it works great only for the first 5 kWh, but after that, the Venus E is depleted.
Do the batteries tell Astrameter their capacity so it can balance them more fairly and maintain a closer SoC? If not, would it be possible to set the capacity of the batteries in the config to allow Astrameter to regulate more intelligently? For example use 5kwh battery for 30 mins and then 15kwh for 90 mins or something like that or maybe you can read the SOC via modbus or openapi which should be possible since you can see the IPs of the consumers?

Thanks for your help!

[sygys]

In the newest version there are sliders for every battery to set the distribution weight. this will help allot in your case. If you really want it distributed evenly based on SoC then Tom has posted an automation here somewhere in these posts that will move the sliders on the fly to keep both batteries evenly charging based on the SoC

[sygys]

Well if it works correct 1 - 3 would mean that when you have 2000 watts 500 goes to the E and 1500 watts go to the D. But if it's not sunny enough and you have rotation turned on it can still be that when the effenciency minimum charge is set, both batteries charge the same amount. When you have set efficiency to 350 watts minimum then the distribution weight will start when power goes over 700 watts. If you never reach that amount one battery will charge at a time and with the rotation they will be equally full in the end.

[TheB1gG]

Then that will sadly not solve my problem. My effenciency minimum is set to 2000 watt because both batteries can output more than that. The inverters are not that efficient, they take 70-80 watt just for turning on, so using both at the same time for medium load is pretty inefficient.

[tomquist]

Note that with an efficiency minimum set to 2000 watts, the second inverter only kicks in if your consumption exceeds 4000 watts. That's probably not what you want, because your Venus can't deliver 4 kW. The efficiency value defines the minimum per-battery value. Also note that there's a 1.2× hysteresis, so once the system is down to one active battery, demand has to exceed ~4800 W before the second one rejoins.

Regarding the weights: they only affect how power is split among batteries that are active at the same time. While the efficiency optimization keeps you in single-battery mode they have no effect. Which battery runs is a plain round-robin rotation (EFFICIENCY_ROTATION_INTERVAL, default 15 minutes) that gives each battery an equal turn regardless of weight, and even a weight of 0 doesn't take a battery out of the rotation.

So for your setup I'd lower MIN_EFFICIENT_POWER to something both batteries can sustain together (or disable it) and let the weight sliders do the balancing. They work as intended as soon as both batteries run simultaneously. I might add a feature in a future version to control the rotation interval per battery, which would let asymmetric setups like yours get weight-proportional turns even in single-battery mode.

[TheB1gG]

Thank you for the info. So I shouldn't set it to higher than 900w since the max for the Venus d is 2200w if I want to continue running single battery mode for efficiency. I will for now disable the single battery mode and check how much energy that wastes over a day and if it would be worth it.
But on the long run having the weigthing system work even in single battery mode would be of course the holy grail.
Thank you both for the insights.

[tomquist]

Yes, that math checks out. With the 1.2× hysteresis the second battery rejoins at 2.4× the configured minimum, and 2.4 × 900 W = 2160 W, just under the 2200 W max of your Venus D. So with 900 W or lower the second battery will always kick in before the first one hits its limit, and you avoid a window where the grid covers the gap.