DC POWER | Battery Charging with Generators

The 12 V DC output of generators are 8.3 A (Amperes, also called Amps). For most users, this might seem sufficient. In reality, many camping enthusiasts find that batteries are not charged at the end of the day, after many hours of running (charging) with the generator. The charging rate in Amperes (A) is too low for the application of camping.

The reason why batteries never seem to really have charged after hours of running is simple; the load connected to the battery almost equals what the generator can supply. Thus, the generator output of 12 V DC @ 8.3 A is only supplying power to the load, and not effectively charging the battery.

There are 2 possible solutions:

1. DISCONNECT THE LOADS

If we assume accessories like fridges, radios or other 12 V DC equipment are connected to the batteries and running while camping, this can affect the battery charging capability of the generator. Assuming all accessories consume on average only 3 A (very optimistic figure) and the generator is supplying its maximum at 8.3 A, we have the following available for charging:

8.3 A - 3 A = 5.3 A

Charging a 105 Ah battery to 80 % at a mere 5.3 A from 30 % state of charge (SOC) with can take approximately 14 hours, if the generator supplies its maximum all the time, which is not actually the case. This means the generator is running at least 14 hours per day, just to keep up with the load connected to the battery.

Disconnecting the load from the battery charging without any loads connected for a few hours can partially solve the problem. Charging time would depend on the size of the battery rated in Ampere Hours (Ah). A 105 Ah battery would need at least 12 hours charging time from 30% SOC (state of charge).

This method, although it seems to work, is slow and might not be what some might want while camping... It just seem to take up too much time.

2. USE A BATTERY CHARGER RATED MUCH HIGHER

Connecting a battery charger to the generator 230 V AC output, will definitely solve the problem, if the battery charger is rated high enough. With this method, the generators' capability of supplying power at 230 V AC is converted to 12 V DC, which will give a much better and more powerful 12 V DC output current.

If we use only 300 Watt from the generator, we divide the power by the voltage needed to charge batteries (i.e. Voltage larger than 13.5 Volt for lead-acid type batteries), and then subtract the load current, we get the following result:

(300 W / 13.5 V) - 3 A = 19.2 A for charging!

Should we use more power (available from the generator), at around 600 Watt, we can see this charging figure grow:

(600 W / 13.5 V) - 3 A = 41.4 A for charging!!!

The following table shows the different output current capabilities when converting power, using a voltage of 13.5 V subtracting an average, more realistic load of 5.5 A:

100 Watt: 1.9 A (Definitely not recommended for deep cycle batteries of 105 Ah)

200 Watt: 9.3 A (Slow charging, consuming a lot of time to reach 80 - 90 % SOC)

300 Watt: 16.7 A (Minimum recommended current for 105 Ah deep cycle battery)

400 Watt: 24.1 A (Good initial charging current for 105 Ah deep cycle battery)

500 Watt: 31.5 A (Recommended initial charging current for 105 Ah deep cycle battery)

600 Watt: 38.9 A (Very good initial charging current for 105 Ah deep cycle battery)

700 Watt: 46.4 A (Maximum allowable charging current for 105 Ah deep cycle battery)

For best battery charging recommendations, contact us for details

PLEASE NOTE:

The figures and results above are under ideal conditions and only obtained from basic mathematics, converting power. Charging currents will differ, depending on the voltage applied, the SOC of a battery (which affects the battery resistance), and other factors (temperature, battery health etc.). These values should be used as an indication of maximum charging currents, that can be obtained by converting the POWER available from the generator.

Now, if we choose the correct battery charger (we recommend a minimum rating 4 times the average load), we can easily keep all accessories connected and running while charging the battery. The load connected to the battery will have minimal effect on the charging time needed to re-charge the battery.

CONCLUSION

If we want to effectively charge a battery using a small silent type camping generator, we need to decide whether we can:

1. Disconnect the loads to compensate for those losses during charging.

2. Use a battery charger rated high enough to charge batteries while supplying loads.

NEED A BATTERY CHARGER TO RUN FROM YOUR CAMPING GENERATOR?

HAVE A LOOK AT OUR BATTERY CHARGERS.

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