# hybrid vehicle DC voltage boost

if i join two battery cells in series then the voltage will be added. what if i replace one of the two battery cells with a DC generator?

My reason is because batteries (excluding Lipo) have modest C ratings, thus the current extracted is modest relative to its size.

In electric cars, batteries are setup in parallel and series (Tesla for example uses 385v) however if I am trying to develop a race electric car, I’ll have to balance between current and voltage, thus if I average out 500–600 volts for a high RPM electric motor then the current extracted from the batteries would be so much that I might kill the battery pack.

Therefore I got this idea of a hybrid system where all the batteries are connected in parallel for current, and then a DC generator is connected in series for voltage.

If I have 2 battery cells connected in series, shouldn’t I be able to substitute one cell with a DC generator is series!!?? I personally think so if we neglect the affect of sinusoidal current which can be solved with a capacitor.

The reason for this system is that if I am trying to develop a high performance electric race car, with this solution I’ll be able to lower the current demand per cell and provide the need for high voltage by connecting the batteries to a DC generator in series.

does this idea work? does it help prolong battery life by reducing current demand per cell?

• Welcome to EE.SE! Think in terms of impedance for everything, battery, generator and load. Do they match up in your case? Also, please draw a schematic. – winny Jan 15 at 7:14
• Firstly thanks for the welcome :-), regarding the impedance, i think we could solve the issue with inductors capacitors and such power systems. Also dont forget that the DC (gasoline) generator is variable speed thus producing variable voltages, which more or less match the electric motors voltage need for different RPM's. i would like to upload an explanatory Sketch however im not sure how in this website. – Sam Al-Hinai Jan 15 at 7:29
• " i think we could solve the issue with inductors capacitors and such power systems" Please show how with a schematic. As the question stands at the moment, it's just handwaving. Press edit on your question and click on the schematic symbol. A pretty full-fledged schematics editor will start and allows you to embed said schematic to your question. – winny Jan 15 at 11:49
• i will soon, thnks – Sam Al-Hinai Jan 16 at 9:12

You could say this system already works. I have a standard full-hybrid. Where a petrol engine works in parallel with the electric motor to move the car forward.

This is also similar to various diesel-electric locomotives, which use an engine to generate electricity which powers a motor. There are some shunting versions of these which use a generator in parallel with a battery pack so that their instantaneous power can be higher than just the engine or the batteries on their own.

Then there are also machines such as the River Simple hydrogen car which uses a hydrogen fuel cells to generate electricity from hydrogen which it then stores in batteries to give good acceleration. Replace the hydrogen fuel cell with an internal combustion engine, and you have your design.

The thing to notice here is that all the systems work in parallel. This is because it is a lot easier to integrate the two power sources in parallel rather than in series. If you have an engine in series with batteries, the voltage out of the system will depend on the power out of the engine. Engines are very slow to respond to changes in loads. Suddenly removing the load will cause the engine to spin up and cause the generator to provide very high voltage for potentially a long (5 seconds or more) time. If the generator is in parallel with the batteries, the engine will always see a load as the external load can be replaced with a load to charge the batteries within milliseconds with ease.

To answer your question: Yes it can work, and indeed does in various production cars (all full and plug in hybrids), as well as locomotives (diesel-electric) and famously on the BBC program Top Gear with the Eagle i thrust.

The important fact is WHY do you have an engine there? You seem to be planning on having an engine there to over come high power/current demands. That won't work too well, as engines are very slow in getting up to speed compared to what can be done with an electric motor and a good battery supply. If you look up the fastest accelerating cars, the world record of 0-60mph (0-100kph) is held by a fully electric car for a reason.

So, in summary; you idea works and is in use today. But for the purpose of extending the range or improving the power delivery of the machine. Putting an engine to over come current spikes is a bad idea due to the slow reaction time of an IC engine.

• thanks for your reply. true there are series hybrid cars already available and work by generating electricity from an ICE generator hooked in parallel. However the load sustained by the batteries is still high when asking the batteries to deliver say (370v and 1000A I.e 370Kw) at full power (96s78p), the petrol engine wont power more than 30Kw of power so the majority will be burdened by the batteries. specifically if i am trying to design a race car with batteries that will last i should lower the current demand per battery cell. – Sam Al-Hinai Jan 16 at 6:05
• therefore by wiring the batteries in parallel im spreading the 1000Amp current demand over more batteries, and the voltage needed will be provided by the 30Kw generator that may produce 400v and 75A current. this way the C rating demand per cell is lowed from 4.2C to about 0.045C only. this way even the cells will almost never heat up ( cells assumed 18650, 3.7V 3000mAh, 7488 Cells) . – Sam Al-Hinai Jan 16 at 6:06
• yes i understand and you are maybe right regarding the delayed response of this system, however is could be solved with capacitors (and yes itll make the system more complex) but the intention is to save battery life substantially – Sam Al-Hinai Jan 16 at 6:08
• @SamAl-Hinai batteries are used in electic and hybrid machines because they are a cheaper, easier and do the job. Lots of hybrid and electric vehicles are on the road after 5+ years, with the original batteries (original prius dates from 1997, and I have seen many with pre-2010 plates on the UK roads today, Nissan leafs are from 2010, and I see many with pre-2014 plates). An extra run of cells in series is a lot easier and cheaper than trying to put an engine in. – Puffafish Jan 16 at 8:27

I’m reading this as equivalent to “can I put a 12 volt car battery is series with a bunch of little 9V batteries to get high voltage at high current (current from the car battery and voltage from the 9 volters)?” I’m afraid it doesn’t work that way. You can’t do voltage and current separately. You have to look at wattage (total power of the circuit).

In this case, the internal resistance of the small batteries would prevent the car battery from delivering much current.