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lifestyle:faq_solar_generator

Words of wisdom: “These aren't aimed at people that know what they are doing.” – LastTreeStar

solar generators

images-na.ssl-images-amazon.com_images_i_51ug3iif-zl._ac_us218_.jpg “Solar Generators” (power stations, power packs) are self-contained devices that contain:

  • a battery pack, often lithium or AGM
  • USB outlet[s]
  • a pure sine wave inverter

These devices are packaged for convenience and are usually much more expensive than the components bought separately.

The terms solar generator and generator alternative are marketing terms with no real meaning: the units do not generate power.

Sometimes the term jump pack is used for portable battery packs in general, but it often means packs intended to jump start a vehicle. Battery pack usually means small, pocketable “bricks” for charging phones and other small devices.

best case scenario

The best use of these “generators” is

  • a person who camps on relatively short outings
  • who can charge from shore power when away from the camper
  • and who does not need to run devices in the camper when the owner is charging the unit

specifications

Specs for these devices are often given in nonstandard or even misleading ways. The following discussion will use the Yeti shown above, although their product description is better than most.

The 33Ah capacity lead-acid battery in the example above is stated as 400Wh. This is technically correct but mixes units in a way that consumers may not understand. Consumers may also not realize that lead-acid chemistries are usually only drawn down to 50% depth of discharge, giving an actual usable capacity of 16.5Ah. In addition, lead-acid battery capacities are measured over 20hrs. With our example this means a 10w continuous DC load in this case, or 9w from the built-in inverter. Loads greater than those will decrease usable capacity due to the peukert effect.

In units with lithium batteries, the DC output of the device will be somewhere between 9v-12.6v due to the voltage of li-ion chemistries.1) On the upside, they have almost no peukert effect and therefore can support heavier loads (at the expense of running time).

You could run run a load at the inverter's 300W normal rating for ~36 minutes.2) Some manufacturers will list the inverter's peak output (600w in this case) in the title as if it were the amount of power the unit could deliver over time. New folk sometimes read this as “I can run 600w of appliances off the unit forever!”, forgetting this is a peak load and that the unit has a finite capacity.

charging

Using the Yeti above as our example again, the charging requirements are:

5 hours from a wall outlet with the included AC charger; in 13 hours with the available car charger*; or as fast as 8 hours from Goal Zero’s monocrystalline solar panels*

Things to consider:

internal AGM batteries

Some units use AGM batteries. This will greatly reduce cost and provide more normal voltage3) but requires diligent charging or the batteries will fail prematurely. All lead-chemistry batteries need to be fully charged then kept charged as much as possible.

solar charging

Note that charging rates from solar panels will be lower than you might expect due to the internal charge controller4). Poly panels will typically make more power in this scenario due to their lower voltage / higher current.

Units that do not mention solar charging in their specs can likely still take solar charging through the DC charging port. Since there may be no controller, manually disconnect the panel when battery voltage creeps up too high. For lead this would be ~15v, and for lithium ~12.3v5). Another rule of thumb is that the cutoff voltage should be no higher than the voltage on the stock DC charger – read its label. Another approach might be to place a shunt charge controller between the panel and DC input and limit the voltage automatically that way. This will not work if the DC port does not “show” the controller the battery voltage.

1) if LiFePO4 is eventually used in the devices then the voltage will be quite close to lead acid's voltage
2) including 10% efficiency loss on inversion, but not including peukert effect
3) compared to 3parallel_serial lithium
4) likely shunt unless otherwise stated
5) assuming 3S
lifestyle/faq_solar_generator.txt · Last modified: 2020/01/14 12:25 by frater_secessus