Can a Powerbank be used to start a car?

[Siwastaja]

Lets say it is a 20Amp powerbank with the sole purpose when built to charge phones and possibly run low current devices.

Consider this unit as the example, 20000mAh Power Bank, ROMOSS Sense 6 Plus USB C Portable Charger with PD 18W QC 3.0

A big discrepancy, first you say 20Amp then 18W, which, at 5V, is 3.6A.

Can you do it? Of course, most stupid ideas are possible. Just wire enough powerbanks in series and parallel. For example, three in series for 15V, 3.6A. Then hundred of these (so 300 total) in parallel for 15V, 360A max. Or oh well, use 600 powerbanks for 15V, 720A for smaller risk of cascading overcurrent detection and shutdown of the units. I'd suggest adding small value balancing resistors, one per each 3 powerbanks in series, such that they drop e.g. 0.5V at 3.6A.

Do a Youtube video of it.

[radiolistener]

PD 18W means that it provides 1.5 Amps at 12V. Since it has USB-A connectors it probably don't support voltage above 12V through PD protocol.

So, in order to get for at least 200 Amps, you're needs to connect 200/1.5 = 134 power banks in parallel (include PD triggers for 12V) in order to use it for a car starter

Also be careful, because if you use PD triggers for 12V, it may be damaged with a car battery which voltage can be up to 13-14V.

If you use USB-C port, you can use 15V PD triggers, but for 18W it can provide just 1.2 Amps at max. So, for 200 Amps you will needs to connect 200/1.2 = 167 power banks in parallel. But be careful, 15V may damage some electronics on your car. Most of all it will be ok, because it was designed for 14.4V and even a little more, but who knows...

[rteodor]

Had one of these starters and it was useful once when due to long standing in cold the car battery was at 4V.
It was also useful to somebody I've borrowed it. For a few weeks he used it almost daily until he replaced his car battery, but he never returned the starter.

I assume that the battery is specially built for the purpose. It has small capacity 55Wh but it is a lot bigger in size than a "domestic" 20Ah/70Wh power bank and a bit lighter. Also it has very thick wires and a 70A relay for protection. That relay is only active for a short period of time after boost button is pressed.

[brucehoult]

Lets say it is a 20Amp powerbank with the sole purpose when built to charge phones and possibly run low current devices.

Consider this unit as the example, 20000mAh Power Bank, ROMOSS Sense 6 Plus USB C Portable Charger with PD 18W QC 3.0

A big discrepancy, first you say 20Amp then 18W, which, at 5V, is 3.6A.

Can you do it? Of course, most stupid ideas are possible. Just wire enough powerbanks in series and parallel. For example, three in series for 15V, 3.6A. Then hundred of these (so 300 total) in parallel for 15V, 360A max. Or oh well, use 600 powerbanks for 15V, 720A for smaller risk of cascading overcurrent detection and shutdown of the units. I'd suggest adding small value balancing resistors, one per each 3 powerbanks in series, such that they drop e.g. 0.5V at 3.6A.

There is no need to use 300 or 600 of the described power banks. There is plenty of energy in just one of them, it merely has to be put into a suitable form i.e. 12V and a few hundred amps for a few seconds.

That is precisely the job the NZ$55 (US$35) device I gave a URL for is designed to do. One of its options is to charge it for 15 min from a USB power source, such as the given power bank. The other option is to charge it from the car battery itself, if it is at low voltage but not completely dead.

https://www.jaycar.co.nz/capacitor-based-12v-300a-jump-starter/p/MB3765

You just need the one power bank and one supercapacitor car starter device.

[sparkydog]

If you use USB-C port, you can use 15V PD triggers, but for 18W it can provide just 1.2 Amps at max. So, for 200 Amps you will needs to connect 200/1.2 = 167 power banks in parallel. But be careful, 15V may damage some electronics on your car. Most of all it will be ok, because it was designed for 14.4V and even a little more, but who knows...

According to Wikipedia: "depending on operating conditions, the vehicle electrical system voltage today can vary between 6.5 and 16 V, with a varying degree of ripple superimposed on this value." From people designing electronics for automotive use, I've heard that such need to be designed to withstand even higher voltage spikes (at least 30V). I would therefore suspect 15V isn't going to be an issue (I'm not warranting that, though!). Alternatively, you could do the sensible thing and disconnect the battery from the car while charging it.

[MrAl]

Hello again,

I see two different interpretations of the original question in this thread, and each one has been answered in a different way because they are two different questions.

[1] The first one is can a car be started SOLELY with a little power bank without there being the original car battery still in the car.
[2] The second is can a car be JUMP started with a little power bank with the original car battery still in the car.

The answer to #1 is NO because the power bank cannot put out enough energy fast enough.
The answer to #2 is YES but it takes time to charge the original car battery with the jump pack first, and it could take as long as an hour, but only if the battery is still good enough to take a charge from a lower current source.

For #2 there are little "power banks" that can work faster, but they are made for jump starting not for just charging phones.  They are hit and miss though because the car has to be able to start fast enough before the jumper pack disconnects from the battery automatically.  These type can put out 16 volts so they can charge the car battery much faster than a regular power bank made for charging just a phone.  Some of them have several Li-ion batteries (or similar) inside so they hold a lot of energy and can deliver it faster than a phone charger.

[shapirus]

[2] The second is can a car be JUMP started with a little power bank with the original car battery still in the car.

The answer to #2 is YES but it takes time to charge the original car battery with the jump pack first, and it could take as long as an

It depends on the definition of "little".

Assuming a fully depleted car battery of, roughly, say, 800 Wh, and not even such a small powerbank of, say, 60 Wh, it becomes clear that such a powerbank does not have a sufficient amount of energy to charge the car battery to the level at which it can output the current required to start the engine sustained during a few seconds.

[Siwastaja]

withstand even higher voltage spikes (at least 30V). I would therefore suspect 15V isn't going to be an issue

Of course it's not going to cause any issue because it's the normal continuous voltage on the car's 12V system during engine run condition. 12V is just a nominal rating. Alternators adjust their output voltages based on temperature, as fully charging the lead acid battery in cold conditions (e.g. -20degC) requires voltage of 15...16V (e.g. the magical 14.4V number won't cut it) in order to not sulfate and self-destruct in matter of months, which is exactly why it's normal to have 15V on the system, and quite obviously everything connected to the car needs to deal with it. Additionally, devices choose to cope with spikes of various durations and voltages based on how robust they need to be, but 15-16V would be the very minimum baseline, as it's both normal and continuous.

[radiolistener]

Alternators adjust their output voltages based on temperature, as fully charging the lead acid battery in cold conditions (e.g. -20degC) requires voltage of 15...16V (e.g. the magical 14.4V number won't cut it) in order to not sulfate and self-destruct in matter of months, which is exactly why it's normal to have 15V on the system, and quite obviously everything connected to the car needs to deal with it.

It depends on the car. On Toyota Corolla I didn't seen alternator voltage above 14.4V. But on another car type I was seen 15V and more... I'm not sure if these 15V is due to broken/failed alternator voltage regulator, or just by design.

Usually alternator has voltage regulator which can control alternator output voltage. It control it by change current through special alternator coils. Sometimes this regulator is failed and alternator can push high voltage on the battery. In such case it leads to a faster death of the battery due to overcharge. The bad thing is that all works ok, and you can even don't suspect that alternator regulator is failed, you can replace battery, it it also will be dead soon. This is why it is important to check alternator voltage in case if your battery is dead too quickly.

But there is also modern Ca/Ca batteries, which may require higher charge voltage than 14.4V, so it's not easy question.

Yes, 15V looks ok, for all vehicle electronics, because it should survive even higher voltage pulses. But who knows, may be some cars don't like when voltage is 15V and more...

[Siwastaja]

It depends on the car. On Toyota Corolla I didn't seen alternator voltage above 14.4V.

You did not measure when really cold, or the alternator regulator circuit was broken (or car improperly designed, but I don't think so for Corolla). 14.4V is about right for summer weather. With cold winters, and I don't even mean Alaska/Siberia tier cold, if you always only charge to 14.4V, the battery never really gets fully charged and in a few months it starts to sulfate and eventually fails to cold start. On the other hand, if you pick say 15.5V which is about right for extreme cold, then you'd overcharge during summer. Lead acid charging really needs temperature compensation (even rudimentary, for example the alternator circuitry of course only measures alternator temperature, there's no sensor at the battery), no way around it (except in lab conditions).

[radiolistener]

Yes, I measured it in summer. I'm not sure if it makes difference depends on temperature, needs to check it.

[shapirus]

Yes, I measured it in summer. I'm not sure if it makes difference depends on temperature, needs to check it.

It does. I once saw 14.85 V on the battery terminals (KIA Sportage) shortly after the engine was started, and that was in the winter, and it was quite cold. In the summer I never saw anything higher than 14.4 V.

However that winter measurement was made with a dubious DMM. Yes it could potentially be THAT off :). I will need to verify it some time.

[MrAl]

[2] The second is can a car be JUMP started with a little power bank with the original car battery still in the car.

The answer to #2 is YES but it takes time to charge the original car battery with the jump pack first, and it could take as long as an

It depends on the definition of "little".

Assuming a fully depleted car battery of, roughly, say, 800 Wh, and not even such a small powerbank of, say, 60 Wh, it becomes clear that such a powerbank does not have a sufficient amount of energy to charge the car battery to the level at which it can output the current required to start the engine sustained during a few seconds.

I had gone all through that in a previous post.

[MrAl]

Alternators adjust their output voltages based on temperature, as fully charging the lead acid battery in cold conditions (e.g. -20degC) requires voltage of 15...16V (e.g. the magical 14.4V number won't cut it) in order to not sulfate and self-destruct in matter of months, which is exactly why it's normal to have 15V on the system, and quite obviously everything connected to the car needs to deal with it.

It depends on the car. On Toyota Corolla I didn't seen alternator voltage above 14.4V. But on another car type I was seen 15V and more... I'm not sure if these 15V is due to broken/failed alternator voltage regulator, or just by design.

Usually alternator has voltage regulator which can control alternator output voltage. It control it by change current through special alternator coils. Sometimes this regulator is failed and alternator can push high voltage on the battery. In such case it leads to a faster death of the battery due to overcharge. The bad thing is that all works ok, and you can even don't suspect that alternator regulator is failed, you can replace battery, it it also will be dead soon. This is why it is important to check alternator voltage in case if your battery is dead too quickly.

But there is also modern Ca/Ca batteries, which may require higher charge voltage than 14.4V, so it's not easy question.

Yes, 15V looks ok, for all vehicle electronics, because it should survive even higher voltage pulses. But who knows, may be some cars don't like when voltage is 15V and more...

Hi,

It is very interesting that you brought this up because I had talked about this on a forum dedicated to automobiles.  The battery voltages on different cars can be VERY different, which does not make sense at all.

On a Hyundai I once had, the voltage was a max of 14 volts, which never charged the battery enough.  I had to bring the battery into the house to charge on a battery charger about once every three months or so.
Also on a Volvo, max 14 volts.
On a Ford Mustang, the max voltage was about 14.2 if I remember right.
On a Buick, the voltage can reach up to 15 volts max, then slowly come down as the battery charges.

From my experience, the lower voltages can only work if the car is driven every day, and it may be questionable at that.
The 15 volt max works the best, because it charges the battery better and also brings the voltage down once the battery gets charged to some degree.  That's the best.

Now one more car, an older Toyota, with max voltage around 13.65 volts.  That's nuts, but I will test that more in the future because the guy just got a new battery so maybe it charges better with a new battery.  If it does not ever go higher than that, then I do not expect the battery to last long unless he charges it manually from time to time.  I don't have much data on that one yet though so I will be measuring the voltage from time to time also to see if the 'resting' voltage drops more and more.  If it keeps dropping, that's a sign that it is not charging enough.

I have not figured out why these voltages should be that different, and nobody seems to really know there are just guesses out there.
There is one thing that sounds like a 'fact' though, and that is the type of battery.  There are the older types and the newer types.  The older types are used in older cars and I think they charge better with lower voltages like 14 volts, while the newer ones are for newer cars that can charge better.  That seems to be a fact because the different battery types are recommended for the different cars, and the newer type chemistries are not recommended for older cars.  This I found out by looking up batteries for different cars.  What I do not know is how much of a difference this makes, as the best info I can find says that there is about a 0.1 volt difference between the two, but I don't know how accurate that figure is.

If someone knows more about this variation in automobile max charging voltages now's the time to speak up.

[LateralNw]

Hi All,

Thanks for all the replies and the interesting detours this question created.
My understanding is it will never charge a 12 v lead acid battery due to the output being only 5V.

So  because it is a voltage Mismatch the 12V lead-acid battery requires a charging voltage higher than 12V, typically around 13.2V to 14.4V depending on the charging stage. A 5V supply is too low to charge the battery effectively.

I got hold of some PD fooler ccts just to see if I could get 12-15V but on my initial test I didn't get any readings, either I wired it wrong or aliexpress sent me a dud?

Again thanks to all for the answers it was quite an interesting discussion.

Cheers, LateralNw

[ataradov]

What is "PD fooler ccts"?

[wasedadoc]

What is "PD fooler ccts"?

What you can place between a PD source and a non-PD sink to make the source deliver the voltage the sink wants. eg https://www.aliexpress.com/item/1005006191468955.html

[mobby_6kl]

Hi All,

Thanks for all the replies and the interesting detours this question created.
My understanding is it will never charge a 12 v lead acid battery due to the output being only 5V.

So  because it is a voltage Mismatch the 12V lead-acid battery requires a charging voltage higher than 12V, typically around 13.2V to 14.4V depending on the charging stage. A 5V supply is too low to charge the battery effectively.

I got hold of some PD fooler ccts just to see if I could get 12-15V but on my initial test I didn't get any readings, either I wired it wrong or aliexpress sent me a dud?

Again thanks to all for the answers it was quite an interesting discussion.

Cheers, LateralNw

I have a 20Ah USB-PD powerbank that can output 15V, in fact I've used it with one of those aliexpress triggers to create a charger for my DJI Mavic Air.  So this part works fine. And yes ~15V is ok for charging a lead-acid battery.

This powerbank has a 74Wh capacity, while a small car battery like I have in my Miata is about 500Wh. So I think it only has a chance of slowly topping it up if it was just a bit low, not completely flat. The maximum output of the powerbank is 30W so it'd take about 2 hours. Then disconnect and try to start. Not great but might be worth a shot if you're stuck in a desert or something.

The other option would be hooking up the lithium cells directly, as they usually have a much higher discharge rate than the electroncis will allow. This is basically like that power tool battery approach that was posted here, and I've seen it done with RC hobby LiPos too. You'd need at least 3 cells thogh and it's questionable if the powerbank cells would like that.

[radiolistener]

A Lead acid battery is considered to have 0% capacity at 11.59V.

No. The lead acid battery parameters are specified for t=25 °C. And it should be recalculated for other temperature.

11.59V for 0% charge is for 65°C (electrolyte density 1.092 g/cm^3)

Normal lead acid battery at 25 °C has the following electrolyte density:
min allowed = 1.070 g/cm^3 = 1.910V per cell = 11.46V per battery
0% charge = 1.120 g/cm^3 = 1.960V per cell = 11.76V per battery
25% charge = 1.160 g/cm^3 = 2.000V per cell = 12.00V per battery
50% charge = 1.200 g/cm^3 = 2.040V per cell = 12.24V per battery
75% charge = 1.240 g/cm^3 = 2.080V per cell = 12.48V per battery
100% charge = 1.280 g/cm^3 = 2.120V per cell = 12.72V per battery
max allowed = 1.300 g/cm^3 = 2.140V per cell = 12.84V per battery

Note that this is EMF voltage which needs to be measured after about 48-72 hours after last charge/discharge.
Immediately after charge/discharge voltage on battery terminals may be different because chemical reactions needs some time to stabilize.

As you can see, it has 0.96 V delta between 0% and 100% charge, so you can simply estimate battery charge level from EMF voltage with this calculation:

Charge level = (EMF - 11.76) / 0.96

Or just round it to 1V delta for 0% to 100% charge and use simplified calculation:

Charge level = EMF - 11.8

which is about 0.1V per 10%.


Regarding to the battery capacity for a car it is usually 60 Ah and can handle starter current 500-700 Amps. The voltage should not drop below 11V.
Which is about 730 Wh capacity and about 6000 W power.


Regarding to the OP power bank, this is PD power bank which supports 12V output (12V x 1.67 Amps on USB-C and 12V x 1.5 Amps on USB-A connector).

But the main problem with OP power bank is that it has just 18 W power (instead of 6000 W as in a car battery) which is not enough to run the starter which needs for at least 2-3 kW. So it is impossible to use it directly.

The second issue of OP power bank is that it has just 74 Wh capacity (instead of 730 Wh as in a car battery). So using it to charge super-capacitor may be also not enough, especially considering the losses on conversion and super-capacitor charging. It cannot replace car battery. But it is possible that using super capacitor charged from this power bank (it will require long time) may allows to start the car for one time in summer.

[JustMeHere]

The car's alternator generates more than enough electricity for the car when the engine is running. The battery is only needed to start the engine and if the car can be stated with the little power bank why do they put such a large battery in the car?

Lead Acid batteries are relatively cheap.  More tolerant.  And don't explode as easily as lithium.  The weight makes little difference to a car.


FWIW....there are starter packs that use lithium batteries that start car from a very dead battery.  No, precharging before attempting to start needed.  For a small engine, they are the size of a flat tissue box.

[Haenk]

The car's alternator generates more than enough electricity for the car when the engine is running. The battery is only needed to start the engine and if the car can be stated with the little power bank why do they put such a large battery in the car?

The idea is to have everything in the car running on the alternator, when the motor is running. At the same time, the alternator *charges* the battery.
On pretty much every car since the last 50 years, there is permanently powered on electronics, from theft protection/alarm, to remote unlocking and ready-to-wake-up computers. This is not nothing, your battery will run out of juice in a couple of weeks (of course this depends on the car) when not being used; you might even run you battery flat when driving only short distances, which drains the battery more on a motor start than the recharging from driving.
So you really need a battery with enough crank power (Ampere) and capacity (matched to the "permanently powered electronics"). Unfortunately, that's not the size of an USB power pack - which might be enough to start your car, but only once or twice.

[MrAl]

Just a quick reply...

Some cars do not start to generate electrical energy with the alternator as soon as the car starts.  This is very strange but it's probably meant to protect the alternator or something.  It could take as long as 5 seconds as my old Volvo did.  That means you need to supply power for a time longer than the time it takes for the engine to start.  If you don't the engine just shuts right off again.  It's a real pain in the neck.  Some jump starters will not start the car because of this because the engine starts, then the jump starter turns off, then the car stalls.  Then you have to reset the jump starter to try again but it will just do the same thing again because of that delay.

[shapirus]

you might even run you battery flat when driving only short distances, which drains the battery more on a motor start than the recharging from driving.

No. The amount of energy spent for starting the motor is tiny. It can be recovered by the alternator in much less than a minute.

The quiescent current, which is consumed by all the devices when the engine isn't running, is a different story, of course. That one is a significant problem when the car is not used frequently enough, especially when it's cold.


p.s. I obviously mean normal cars that don't consider themselves smarter than the user. If there's some weird charging logic, then of course anything may happen, like in this quote

Some cars do not start to generate electrical energy with the alternator as soon as the car starts.  This is very strange but it's probably meant to protect the alternator or something.  It could take as long as 5 seconds as my old Volvo did.  That means you need to supply power for a time longer than the time it takes for the engine to start.  If you don't the engine just shuts right off again.  It's a real pain in the neck.

[Marco]

This is legit. Supercap based jump starters definitely work.

The amount of energy required to start an engine is very -- surprisingly -- low. Even a half-dead car battery contains more than enough of it. But the problem is that this energy must be released in a very short time, and this is what a depleted or degraded lead-acid car battery is not capable of. A sufficiently large supercap bank, OTOH, can do it, and with a proper charging circuit it can be charged from any low-power source, including a powerbank, that would never be able to start an engine on its own.

Seems a good evolution, the li-ion ones always seemed a bit iffy to me.

Some of them also have a timer I see. So you press a button, jump in the car and start when it beeps so the battery doesn't drain the capacitors before you have a chance to start. If the battery isn't completely buggered that should work most of the time and you won't have to disconnect it (though you can when necessary).

[amyk]

Just a quick reply...

Some cars do not start to generate electrical energy with the alternator as soon as the car starts.  This is very strange but it's probably meant to protect the alternator or something.  It could take as long as 5 seconds as my old Volvo did.  That means you need to supply power for a time longer than the time it takes for the engine to start.  If you don't the engine just shuts right off again.  It's a real pain in the neck.  Some jump starters will not start the car because of this because the engine starts, then the jump starter turns off, then the car stalls.  Then you have to reset the jump starter to try again but it will just do the same thing again because of that delay.

That reminds me of how dynamos that need to self-excite slowly build up voltage from residual field magnetism, and suggests that perhaps your alternator's field excitation circuit isn't working correctly, since automotive ones are normally excited from the battery too, commonly through the charging indicator:

https://electronics.stackexchange.com/questions/599265/does-alternator-self-excitation-require-rectification