Power Supply

Various ~5 V DC power supplies for ultralight blower stove are considered with regard to; convenience, efficiency, versatility, rechargeability, backup power and safety issues. The 18650 lithium-ion battery is my preferred battery and it packs so nicely amongst stove components.

The blower unit and the little lighting module is designed to run on approximate 5 V DC. If the correct polarity is reversed, the motor will not run and no harm is done. The fan draws approximately 0.29 A without any air constriction and 0.26 A with the shutter closed.

“No I have not made a mistake, it is counterintuitive to some, but there is less current with the shutter closed because the motor can do less work! it is the same with water pumps.”

There will be an extra 0.02-0.03 amps with the LED light running.

The fans have brushless motors and are designed to run on a regulated 5 V DC. They appear to run quite happily at 6 V. They also can run unhappily (a bit rough) down at 2.5-3 V. One power supply option below (AA battery box) can have full and half voltage output wires, so that it can provide for two fan speeds to allow gentle cooking or simmering and also doubles the cooking time from a set of batteries.

Blower stove power energy ratings

For all the battery power supplies that I have tested, I determined that they do not provide the amount of electrical energy that I would expect by estimation from the battery label (see later discussion ‘Battery performance, energy yield and safety issues’ below.

“Let’s be clear about this, this is not a complaint, I am delighted with all of my listed battery options, it is just that my simple tests of time, voltage and current and estimated losses through the voltage step-up circuit never agrees with the battery’s label rating and I don’t know why it should be so? There is a generous amount of cooking time available in all the lightweight power supplies that I consider and the cheapest ones provide excellent value (the most rechargeable cooking hours for the least space, weight, environmental waste and cost). All power supplies will delight outdoor adventurers (other than the most mean spirited ones) who discover this new way of cooking “

Power supplies

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AA battery box. This was my first power supply for my early stoves and I have used them for many years. The box holds 4*AA batteries, has an on/off switch, positive (red) and negative (black) output cables. The batteries are series-connected. I add a third wire in the middle of the battery train to give two alternative half voltage power sources. This enables a slow fan speed to provide more gentle cooking. It also can double the cooking time from a set of batteries.

I fit the robust copper pin connectors on each wire that will connect to the inputs of the blower fan (or the LED Snorkel Lighting Module. This arrangement provides for multiple hours of cooking at full power or more at half power depending upon the quality of the batteries. This is the bulkiest of my power supply options, but it still fits into my smallest Solo stove (a large coffee cup size) with room for all other stove components.

The biggest advantage of this power supply is its simplicity and the fact that extra batteries can be carried for little extra weight for long trips. To me, the downside is that with non-rechargeable batteries you don’t know how many hours of cooking time is left and I find that rechargeable ones are rather disappointing, particularly in a cold mountain environment. The effect of coldness on battery performance can be mitigated by keeping the batteries warm with heat from the stove, but the balance between too cold and too hot is not easy to manage. The USB power pack with removable 18650 lithium-ion battery’ is better in this regard (see later).

Unfortunately, for the three cable configuration, the on/off switch does not isolate all cables. There is a potential for battery shorting if the copper pins make contact with one another or a metal object. Consequently, to isolate the copper pins on the power cable they should be placed in the tight holes in the rubber terminal block that is mounted on the centre tap cable.

The remaining power supplies are less prone to this type of shorting issue, because the positive and negative pins have a fixed spacing and the plug that goes into the USB power supply is effectively the on/off switch for the blower fan and users should keep this plug out of the power supply when power is not being used and when it is being transported.

Luckily, for the following USB power supplies,  If the power cables were left in the power supply it makes it much more difficult to pack up. In addition, the devices are short protected, but common sense tells me that good safe practice should come first.

Also, disconnecting the power cable from the power supply and leaving it connected to the blower fan makes the cable less likely to be lost!

Aldi solar USB power pack. This neat little unit was the one that I used next after many years of use of the ‘4*AA system’. It has 5 V step-up circuit, inbuilt battery charge/discharge management with short protection and indicator lights.  It has a 3.5*1.35 jack output socket and USB micro charging socket and charging cable. It will provide for ~2.5 h of powerful cooking and will fit easily inside all my cooking stoves and is much less bulky than the ‘4*AA box’. It is great for short walks, day trips and picnics where it is nice to have a cook up. It avoids the cost and wastage of using normal batteries and gives a known amount of cooking time if fully charged. Charging on USB supply is simple. However, unlike the AA battery option, when using the USB battery blower it will just stop without any warning when the discharge protector just cuts the power (as it should) when the battery low voltage is reached.

I have found that the solar charging function is ineffective enough to give useful battery top up when cradled on top of my backpack while bushwalking. The device does not allow battery changeover, so carrying spare batteries is not an option.

The connection to the Aldi USB unit is described my power plugs page .

USB power pack with removable 18650 lithium-ion battery. To date, this is my most effective, compact, versatile and cost-efficient power supply. The replaceable  18650 lithium-ion battery fits inside a compact cylindrical aluminium case. It comes with inbuilt; 5 V step-up circuit, battery charge/discharge management with short protection and indicator lights. It has a USB A output socket and USB micro charging socket (as used for Android phones).  It provides ~2-3 h of full power cooking. I consider it to be superior to the Aldi power supply as the 18650 battery is removable and can be easily replaced when needed on long walks. Its slim profile makes it easy to pack inside the stoves and easy to mount on the blower manifold so the whole assembly with electronics moves as one. This arrangement helps to keep the battery warm in cold weather and minimizes the risk of damage to the power cable.

Large USB power bank. I have recently tested a large power bank and it ran the blower fan for over 30 h. This may be a good choice for stump burning. However, I consider the disadvantages of this type of power supply are many; considerable weight, long charging time with a small backpack charger, not easy to keep in ‘Goldilocks temperature zone’.

I consider that multiple 18650 batteries give better backup insurance rather than having ‘all eggs in the one basket’. Multiple small batteries make it easy to monitor power reserves and budget for appropriate use on extended trips.

Blower Stove Power Management Issues

Integrated battery cradle. My latest design incorporates a cylindrical cradle for the USB 1860 battery power supply (shown below). This means that when deployed the blower and power supply all move as one. This makes it compact, easy to handle, less likely to lose parts in the darkness and eliminates straining of the fine fan cables. The 18650 battery is housed in a thermally conductive aluminium power pack tube and should not be allowed to get too hot for safety reasons, nor too cold for good function, the cradle makes a ‘Goldilocks-zone’ where both conditions are met on a cold night or in the snow.

Battery performance, energy yield and safety issues.  Because I consider the lithium-ion 18650 battery (in a USB power pack) to be the most economical, weight-efficient, compact, ‘environmentally sustainable’ and versatile power supply option it is worth discussing its potential limitations and mitigating actions.

There are quite a lot of negative comments about ‘cheap’ 18650 batteries and power pack performance with regard to; energy capacity not meeting the label value, ability to be recharged many times or cycle times and safety issues such as exploding batteries.

There are also concerns about cheap USB power packs that use 18650 lithium-ion batteries having low efficiency of voltage step up conversion ~70% and premature charging cut off.

I have used a combination of cheap lithium-ion batteries in a cheap USB power pack to run the fan without any noticeable fault or evidence of overheating. The power pack manages both the charging and discharging of the battery including short protection. According to the battery label, the battery is also SUPPOSED to have ‘short protection’ circuits within (see later comment).

Evaluation of battery performance issues. The cheap 18650 batteries that I use are labelled with “4000 mAh 3.7 V”, “500 recharges” and “Over-Current Protection (OCP) and Short-Circuit Protection (SCP)”.

Available electrical energy. I calculated the available electrical energy of the battery from the label to be 14.8 Watt hours (4 Ah*3.7  V). Using the above voltage step-up energy conversion factor of 0.7 this reduces the energy to 10.4 Watt-hours. For 10 cycles I tested the same battery running the fan, without air restriction and with the LED light running (as a visual indicator) till the low voltage control cut the power. In these tests, the fan ran for an average of ~2.54 h and each battery provided an average of ~4 Watt-hours per recharge. This was estimated by the combined fan & LED current*USB voltage*system runtime ((0.29+0.03) A*5 V*2.5 h) and this is about 40% of the expected energy output from the label.

Either the battery does not come up to label expectations for available energy content (in my experience they seldom do)  or the voltage step-up factor is less than the 0.7 assumed in my calculations.

“To me, simply creating 2-3 hours of renewable and powerful cooking with the aid of such a combination of cheap devices is a delight and you would be hard to please if don’t think so. It will owe you very little when it dies”.

Short circuit protection of the USB power pack. I tested the combination of the battery in the USB power pack by inserting the power cable with the exposed ‘fang fitting’ (described below)  on the end of the cable. This fitting when only partially inserted into the socket leaves exposed copper conductors that can be shorted with a piece of wire. I ran the fan and the LED light and the blue USB power active light illuminated as expected. When I shorted the fang fitting it immediately stopped the fan, LED light and the indicator light until the short was removed. I also noted that there was no visible spark from the short circuit.

“It appears that the short protection of the USB power pack is good from a safety perspective, it does what you would want it to do. However, I don’t rely on this safety feature and use common sense and remove the cable when not in use and allow the smarts in the power pack to be my ‘fail-safe protection’.”

As an aside, during this testing, I noted that when the LED light was run alone, without the fan connected, it did not cause the USB power pack indicator light to illuminate. This means that small currents of 0.02-0.03 A can flow from the power pack without you knowing about it and could waste your battery.

“Always remove the cable from the power pack when not in use and leave it connected to the blower unit so it does not get lost or left behind.”

Lack of short circuit protection of the 18650 battery. I cautiously tested the fully charged battery by connecting a wire to the negative end of the battery and brushing the positive terminal with some of the fine frayed wires at the other end of the cable. Yes, there were plenty of sparks and some of the wire melted.

“This is not my idea of short protection so cable removal and the USB power pack will be your real protection.”

The above video of the exploding battery was arranged by extreme provocation. The short protection of a power pack was bypassed, the thick plastic protective insulation disk was removed from around the positive terminal and a large conductor (metal washer) was used to set up the shorting situation. Even then I noticed that it gave plenty of warning of fumes and spewing liquids before the final explosion.

I have concluded that with care and common sense that some cheap 18650 lithium-ion batteries when used in a suitable cheap USB power pack with short protection, that is known to work, should be safe. 

Good Value for money power supply. Providing they are safe, consider a battery and power pack costing $5.0 ea, buy the time the battery has been used only 10 times at 3 h/use it will be a cost of 13 cents/hour ($5 /( 10*4)) and it will probably provide many more cycles than this.

All the batteries above provided adequate energy for the task and are excellent value for money compared to manufactured hydrocarbon fuels for cooking stoves and are capable of providing multiple hours of cooking pleasure for a fraction of the weight and cost of these fuels.

Polarity issues. While correct polarity is essential for the fan and the LED light to work, there is no harm done to the LED, fan or battery if the polarity is reversed. The motor is polarity protected and the LED will simply not work if the power pins are inserted in the wrong holes. Obviously, remove the cable in this situation as a small current can flow and discharge the battery.

Backup power considerations. For any trip, I take a backup battery. I prefer the 18650 Li batteries in the USB power supply and at ~45g/battery this is a small extra load to carry. They are also good for lighting and charging devices in emergencies.

Tim

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