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Do you find that your off-grid solar system batteries are low on charge when you need them?
Are you wondering what may be drawing the battery power?
Batteries may be drained by solar panels, charge controllers, and appliances.
This post looks at whether inverters drain batteries, how fast they drain, and how battery drain by the inverter can be stopped.
Does an Inverter Drain the Battery?
Yes, a power inverter can drain the battery even when idle, i.e. no appliance is connected or switched on provided the inverter is switched on and in standby mode.
The amount of power (and current) an inverter draws from a battery depends on the inverter design.
Some inverters draw more power than others. To find out your inverter’s power draw, consult the technical specifications section of the inverter manual.
Look for the inverter’s no-load power consumption (watts) or no-load current(mA). You can work out the no-load power consumption (watts) by multiplying the no-load power current by the inverter voltage.
A 1000 watt/ 12V inverter with a no-load power consumption of 7.5W continuously draws 7.5W or 0.63 Ah of the battery capacity even when no appliance is connected.
The no-load power consumption of the inverter mainly depends on:
- Inverter efficiency. You should aim for an inverter efficiency of 90% or greater. More efficient inverters have a smaller power draw compared to the less efficient inverters.
- Inverter size (watts). Larger size inverters generally have a higher power draw on standby compared to lower wattage inverters.
Avoid using inverters with a higher power rating (watts) compared to the connected appliance’s power consumption.
The no-load power consumption can be significant in comparison to the appliances powered.
Will an Inverter Drain the Battery?
A power inverter draws power from the battery when switched ON and in standby mode. To stop the inverter from draining the battery, switch it off (turn its ON/OFF switch to the OFF position).
Some inverters have an energy-efficient setting that can reduce the power draw by about 80% when the inverter is on standby.
Check if your inverter has that option.
How Fast a Power Inverter Drains the Battery?
How fast an inverter can drain a battery mainly depends on the power inverter’s no-load power consumption and the available battery capacity and the state of charge.
Take for example, a 1000 watt/12V inverter with a no-load power consumption of 7.5 watts.
If it is connected to a 100 Ah fully charged AGM battery, the available capacity is 12V x 100 Ah = 600Wh.
The battery will be drained to 50% of its capacity in 80 hours or 3.3 days.
Larger capacity inverters tend to have a higher no-load power consumption and if so will drain the battery in a shorter time.
How Long your 12V Battery Lasts with an Inverter
The table below shows estimated times to drain a 100Ah battery to 50% of its capacity with selected inverters loaded to 100% of their capacity (watts).
|No.||Appliance power consumption (watts)||Estimated runtime|
|1||100||About 5 hours|
|2||200||About 2.5 hours|
|3||300||About 1.5 hours|
Why your Inverter Battery may be Draining Fast?
If the inverter batteries appear to be draining faster than usual:
#1. Double-check that there are no appliances running that may have been accidentally left ON. It is possible that the batteries appear to be draining fast because of additional appliances (s) switched ON.
#2. Confirm that the inverter batteries are fully charged. It is possible that the inverter batteries are partially charged or not charged at all creating the mistaken impression that it is draining faster than usual.
Are the battery terminals clean and firmly connected to the alternator or charge controller? This can affect how well the inverter batteries charge.
Also, confirm that the charging source – the charge controller, battery charger, or car’s alternator is actually supplying power to the battery.
You can connect a current meter to the cable connecting the charging source and the battery to monitor and confirm that the batteries are charging.
#3. Your batteries may be aging and have lost their capacity to hold charge. How old are the inverter batteries and how many cycles are they expected to last.
As batteries age, you can expect them to lose the ability to hold charge and will drain faster than usual even when fully charged.
Can an Inverter Kill a Battery?
Yes, an inverter could possibly kill a battery by deeply discharging it beyond the recommended voltage (repeatedly).
Battery lifespan reduces when they are deeply discharged repeatedly beyond the recommended depth of discharge, 50% for AGMs and 80-90% for LiFEP04.
At 10.5V, when the low voltage disconnect is activated, the battery is already drained.
How to Stop an Inverter from Draining the Battery?
Inverters will usually have a low voltage disconnect feature that shuts it down as low as 10.5V DC. Unfortunately, the low voltage disconnect voltage is usually set at too low a voltage.
By the time it is triggered, the battery is usually completely drained. To stop the inverter from draining the battery when no appliance is connected, switch it off.
If the inverter has an energy-efficient setting, you can engage it to reduce its drain on the battery and extend how long the battery lasts.
In addition, you can also install a programmable low voltage disconnect switch that disconnects the inverter at a higher voltage before the battery is fully drained.
An inverter can drain the battery if left switched ON. The power draw largely depends on inverter design. More efficient or smaller inverters tend to have a lower power consumption when on standby compared to inverters with a larger rating.
To stop the current draw, switch off the inverter when not being used. You can limit its no-load power consumption by engaging its energy-efficient mode setting (if it has that feature).