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lifestyle:faq_solar_generator

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

The self contained units are overpriced, underperforming “power for dummies”. – Somebodyelse1)

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. Sometimes manufacturers use non-standard panel connectors to keep customers in an expensive “walled garden”, referring to normal, non-proprietary panels as "off_brand".2)

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.

Ah are often expressed as mAh. Which is more impressive, 33Ah or 33,000mAh? They are the same capacity expressed in different ways.

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 typical 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 and their 3S internal arrangement.3) Nefarious marketers sometimes multiply each cell's Ah rating times the number of cells, resulting in a 3x inflation of Ah rating.
On the upside, they have almost no peukert effect and therefore can support heavier loads (at the expense of running time). Also, higher end units run 4S or higher voltages then downconvert them for a ~13v output much closer to what nominal 12v devices expect.

You could run run a load at the inverter's 300W normal rating for ~36 minutes.4) 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:

Charging from solar panels

Charging these devices from solar panels will probably be slower than you might expect.

  • in the absence of an mppt controller5) panel output is hamstrung by battery voltage. You may see a device listing 60w max input but specifying a 100w panel for use with it, and now you know why.
  • devices with 3S lithium cells will hamstring the panels even worse6)
  • long wire runs (as seen with portable panels set outside) result in voltage drops
  • sunlight is limited to a certain number of hours. Some units require more hours of charging than there are hours of sunlight in a day.

Poly panels will typically make slightly more power on normal (non-MPPT) devices due to poly's lower voltage / higher current. Devices with internal MPPT controllers will use both panels equally well because they decouple battery and panel voltages.

Note: it is possible to place a small DC-DC converter between the panel and input port to get the panel up near max power. Doing so will make it even more important to manually disconnect the panel when charging is complete.

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 ~12.3v7). Another rule of thumb is that the cutoff voltage should be no higher than the voltage on the stock DC charger – read its label. Be certain not to exceed the maximum input charging voltage.8)

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.

Charging from wall socket

Wall charging is typically fastest because the manufacturer gets total control over the adapter's voltage and current output. Note that they might not include a fast charger to reduce cost or heat stress on the battery.9)

Charging from car outlet

Car charging is typically slow because alternator voltage tends to be fairly low10) and ciggy outlet current limited to 10A. Unless one is on a road trip there is probably not enough time spent driving the vehicle to charge the device fully.

internal AGM batteries

Some units use AGM batteries. This will greatly reduce cost and provide more normal voltage11) 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.

2) COUGH inergy COUGH
3) if LiFePO4 is eventually used in the devices then the voltage will be quite close to lead acid's voltage
4) including 10% efficiency loss on inversion, but not including peukert effect
5) sometimes present on higher-end devices
6) 3S Li voltage can be as low as 9v, and maxxes around 12.5v.
7) assuming 3S
8) typically 20-25v for built-in MPPT controllers. Standalone controllers typically can handle much higher input voltages – check the specs.
9) particularly for Li
10) particularly for charging lead
11) compared to 3parallel_serial lithium
lifestyle/faq_solar_generator.1589989162.txt.gz · Last modified: 2020/05/20 08:39 by frater_secessus