
Portable power stations (or PPS) are extremely popular in the nomad community. These large batteries are designed for convenience and ease of use, and they are a great solution for many uses. In terms of battery capacity and run time, power stations are typically quite expensive for what you get, and they do have other drawbacks.
Related terms
"Solar generator" is a common but misleading term for portable power stations: these devices do not generate any power by themselves and do not contain solar panels. Rather, you can plug solar panels into them to create power. The term is a double reference: first, when portable power stations were introduced, they replicated the function of conventional fuel-powered generators (power where and when you need it), and second, you could plug a solar panel into it to recharge the battery.
Power stations are really self-contained electrical systems. Other terms may include "generator alternative", "rechargeable portable battery". (The term "jump pack" typically refers to systems designed to jump-start a vehicle; these are not designed for powering small electronics and appliances. "Battery pack" typically refers to small, pocket-size batteries designed to recharge phones and other small devices.)
What's in portable power station?
These devices contain:
- A battery, usually LiFePO4
- One or more USB outlet(s) and 12v outlet(s)
- Inputs to charge the battery via AC (household/grid) power, 12v plug from your vehicle, and a separate portable solar panel.
- Internally, they contain a battery management system, an inverter, and a solar charge controller.
Benefits
Compared to an installed electrical system, a portable power station has these benefits:
- Ease of use
- All-in-one convenience: No need to understand how batteries or electrical systems work
- A fast solution if you quickly need power on the road: great for involuntary nomads
- Portable: Use it away from your vehicle when needed (at a camp site, etc.), move it between vehicles
- Multiple recharge options: attach portable solar panels for charging all day; plug in at home, work, or elsewhere; plug in to 12v car charger (probably slow) while driving.
- Multiple ways to power devices
- Great for short trips and limited power needs
- Good as a backup to an installed electrical system
Disadvantages
Compared to an installed electrical system, a portable power station has these disadvantages:
- A relatively expensive way to store power.
- Recharging the power station may be too slow to meet your needs.
- Almost always more expensive than all of their components purchased separately.
- If one internal component breaks, the whole thing may be useless.
- Repairs are difficult or impossible and may void warranties.
- Some manufacturers use proprietary non-standard connectors to keep you in an expensive "walled garden": charging cords and battery expansions can only be purchased from the original manufacturer; if the manufacturer stops selling the product, replacements may not be available.
- Low-end models may use cheaper internal components: AGM battery instead of lithium, MSW inverters instead of PSW, and a PWM solar charge controller instead of MPPT; more restrictive charging limits.
- May have fewer recharge cycles (a shorter useable lifetime) than a similar-sized installed system
Specifications
Unfortunately, specs for these devices are often given in nonstandard or even misleading ways, so it's important to be careful when comparing models and making a purchase. We are most interested in:
- how much capacity the bank has (typically in Watt-hours, Wh)
- charging limits
- by car adapter (typically ≤120w because of limitations of the ciggy port)
- by wall adapter (volts and amps, sometimes the stock wall charger makes lower power than is otherwise possible)
- by solar (Voc and input current, which will dictate which panels and how many are suitable)
- DC output (typically 10A at 12v)
- AC output (given as Watts, the biggest AC loads you can run)
Capacity and output
Capacity is most often listed in Wh (watt-hours), which makes comparison quite easy. Some (especially lead cells) retain Ah ratings. For lead batts, 12v x the Ah rating = Wh. Sometimes Ah are expressed as mAh, or 1/000th of an Amp. Which is more impressive, 33Ah or 33,000mAh? They are the same capacity expressed in different ways.
Nefarious marketers sometimes multiply each battery cell's Ah rating times the number of cells, resulting in a 3x inflation of Ah rating.
If the battery is lead-chemistry (AGM, etc.), only about 50% of capacity should be used in order to ensure a long life.
- For example a 400Wh battery has about 200Wh usable.
- With 200Wh usable we could run the a theoretical 400w inverter at max load for 30minutes: (200Wh / 400W x 60 minutes)
If the battery is lithium, about 80% of the rated capacity can be used and still hit the manufacturer's cycle life claims.
- For example, a 400Wh battery has about 320Wh usable.
- With 320Wh usable we could run the a theoretical 400w inverter at max load for 48minutes: (320Wh / 400W x 60 minutes)
Some units are tightly focused on inverter (AC) output, and don't have big DC outlets. The BLUETTI EB150, for example, maxes out at 9A DC and that is through the ciggy outlet.
Cell chemistry
The cell chemistry is likely 3.6v Li-NMC ("Li-Po"), unless LiFePO4 is stated. The chemistry has significant impact on both battery cycle life and solar charging behavior. (when PWM charge controllers are used; see below).
Li-NMC are typically 3.6v cells arranged three in a row (3S) for nominal 10.8v. Actual voltage will vary from 9v-12.6v. Some more expensive models use 4S for 12v-14.4v but this is uncommon. Li-NMC are rated ~500 cycles to 20% state of charge.
- LiFePO4 are typically 3.2v cells arranged four in a row (4S) for nominal 12.8v and actually ~12.1v - 14.0v. LiFePO4 are ~2000-3000 cycles to 20% SoC.
- SLA (lead) batteries are uncommon. They are nominal 12v and actually ~12.1-14.6v. SLA as found in solar generators are capable of ~500 cycles to 50% SoC.
Inverter
The inverter will usually be pure sine wave, but lower-priced units that do not specify may be modified sine wave. Modified sine wave is not appropriate for some electronics and appliances.
Inverters are typically rated on their continuous output but unscrupulous marketers may list the peak load, which is a temporary overload.
Solar input
If the solar charge controller isn't specified as MPPT, it is likely the cheaper PWM.
Solar charging limits
Many smaller units have quite restrictive solar input limits.
- Voltage - 22Voc is a common voltage limit, effectively limiting one to 12v nominal panels.
- Current limit - 3A is a common input current limit on smaller, less-expensive units.
- With PWM controllers the max power harvestable will be 3A x [internal battery voltage], which can be as low as 9v. 9v x 3A 27w.
- MPPT controllers with the same limit might run the panels at 18v, the Vmp: 18v x 3A = 54w((minus DC-DC conversion losses of ~5%))
Pass-through charging
Pass-through charging is an important feature, as it allows you to run DC/USB/AC while charging the unit. Some units will pass through DC but not power the inverter for AC. Check the specs and reviews carefully. While passing-through keep an eye on the unit's temperature and discontinue one or the other if it gets too warm.
A unit with pass-through would maximize charging while driving; both the solar generator and attached devices would charge: 12v ciggy port -> SG -> other devices. A unit without pass-through could only charge the SG because the power cannot be "passed through" the SG.
The situation with solar would be even worse, because it might take all day to charge from solar and the SG could not power other devices for that day.
Regulated DC output
Since many of the devices don't run at 12v-friendly voltages, some of the nicer ones have voltage regulation. This means the output would be a steady 12.8v or 13.4v (whatever they decide) no matter the voltage level of the internal battery pack. Unregulated 3S packs can drop to 9v, causing some devices to misbehave.
Charging
Charging requirements might be stated as something like: "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:
- will you be near shore power for 5 hours to charge from 110vac?
- It takes 13hrs to charge from a running vehicle because alternator voltage output is relatively low.
- Idling your vehicle to charge is a really bad idea.
- Will you have 8hrs of usable solar harvest? Do check the Vmax and Imax specs for the device if you intend to charge with solar; the max input voltage is usually quite low.
Charging from solar panels
Charging these devices from solar panels will probably be slower than you might expect:
- If the unit has a cheaper PWM controller, panel output will be 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 worse: 3S Li voltage can be as low as 9v, and maxes around 12.5v.
- 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.
- it is common for smaller units to have low input voltage limits, like 25v or lower. This restricts the panels you can use for charging.
- it is common for smaller units to have low input current limits for DC charging (wall adapter, car adapter, or panel). This is particularly restrictive on panel input. Consider these examples using a 3A input limit and 100w panel with 18Vmp.
- 100w panel on MPPT controller - 18v x 3A = 54W (In practice it will be even lower due to cell temperature derating. 10% derating would put max input around 49w.)
- 100w panel on PWM controller - With typical 3S Li-Po batteries input would typically be limited to something like 36w (12v x 3A). Less-common internal AGM batteries would make a bit more since voltage is higher, ~39W (13v x 3A).
Poly panels will typically make slightly more power on 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.
Adding MPPT charging
Some of the newer Goal Zeros have MPPT chargers built into them, which does increase their usability. To older models, it can sometimes be added.
Goal Zero makes an optional MPPT controller that installs seamlessly into selected models. Will Prowse damns it with faint praise, noting the 22v solar input voltage limit and relatively modest yield improvements: "It does work better than the PWM on the goal zero... it's worth the money but not as good as a DIY system[2] The GZ display will not show the charge rate from external controllers.
It may be possible to run the output of a standalone MPPT controller into a charging port of the device. Remember to configure the controller to put a max voltage in line with what the AC charging adapter puts out. See this video by Will Prowse.
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 ~12.3v (assuming 3S). 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 — typically 20-25v for built-in MPPT controllers. Standalone controllers typically can handle much higher input voltages — check the specs.
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, particularly for lithium.
Charging from car outlet
Car charging is typically slow because alternator voltage tends to be fairly low (particularly for charging lead) 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.
It's not efficient in the normal sense, but if ciggy charging is running <100w it might make sense to charge the device with the AC adapter running on an inverter rather than from the car charging adapter: 12v ciggy port -> small inverter -> AC adapter -> device
Example: the BLUETTI AC50S charges about 2x as fast from the inverter than from the car adapter, due to the AC adapter's higher 27.5v output.[3]
Charging from isolator
If >120w charging is required while mobile, one solution might be to install an isolator as one would when charging an auxiliary battery. The isolator will pass heavier current into the cabin of the vehicle: alternator -> isolator --> inverter --> solar generator's wall adapter. As with the ciggy lighter setup above, it's not particularly efficient but while driving the alternator has power to waste.
Internal batteries
Some units use AGM batteries. This will greatly reduce cost and provide more normal voltage (compared to lithium) 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.
Manufacturers
The most common "premium" brands:
Lesser known brands include:
Cheaper units may be high-value rebadged units, or they may be lacking features. Read and understand the specs so you know what you are buying.
They tend to be named after the watt-hours (Wh) of battery capacity (at 100% DoD, which is unrealistic), or sometimes by the inverter output rating.
The manufacturers often sell proprietary panels (Jackery Solar Saga, etc) which are needlessly expensive. Do the homework and find out which normal panels can work with your device (voltage and amps); most will require an adapter. Will Prowse recommends devices with MPPT controllers.
Notes: inverter ratings below are the continuous rating, not peak/startup rating. Lithium packs are typically duty-cycle rated to 80% of capacity. Inverter runtime estimates are 100% of continuous rating at 80% DoD and 10% inversion losses. (Jackery advises 15% inverter losses in the Amazon listings, but 10% is used here for consistency.) Inverters described below are pure sine wave (PSW) unless described as modified sine wave (MSW).
DIY portable power stations
People who want portability or an all-in-one solution can build their own solar generator out of a trolling battery box or milk crate. In this approach the battery, inverter, solar charge controller, and DC power ports are installed in or on the carrier. See Will Prowse "milk crate" how-tos
Needs assessment
Product assessment
- How well does the product under consideration meet the needs above?
- How effectively will it charge from your chosen sources?
- If it meets your needs, does it do so at a price you are willing to pay?
Resources
Search Amazon | Search Amazon for related products. | |
Search forums and groups | Search van life discussion groups for "portable power stations" | |
Search related sites | Search van life sites for "portable power stations" | |
Search NomadLife.wiki | Search other pages on this wiki for "portable power stations" |
- ↑ For image credits, open image and click More Details
- ↑ https://www.youtube.com/watch?v=rqXscD69RvM
- ↑ https://www.reddit.com/r/overlanding/comments/o8orti/newbie_question_on_jackery_bluetti_portable_power/h42jvr3/?context=3