Enginer Plan B

[sipnfuel]

Can I ask a stupid question:

How come the battery packs can not be connected in series in such a way that the voltage is 240V?

[mrbigh]

Originally Posted by sipnfuel

Can I ask a stupid question:

How come the battery packs can not be connected in series in such a way that the voltage is 240V?

I will sugest you to go to the Enginer website and get interiorized with their principle of operation and also to read the ample content of CalCars for more in depth information on any PHEV conversion.
Regards

[sipnfuel]

Originally Posted by mrbigh

I will sugest you to go to the Enginer website and get interiorized with their principle of operation and also to read the ample content of CalCars for more in depth information on any PHEV conversion.
Regards

I know how the system works overall.

I'm not familiar with how many cells are in the battery pack however. Are there multiple 48v battery packs connected in parallel? Or just one battery pack containing 16 cells?

I know the converter will stabilize the output voltage, of course that is a good reason for its inclusion.

[electric1]

Originally Posted by sipnfuel

I know how the system works overall.

I'm not familiar with how many cells are in the battery pack however. Are there multiple 48v battery packs connected in parallel? Or just one battery pack containing 16 cells?

I know the converter will stabilize the output voltage, of course that is a good reason for its inclusion.

That depends on your definition of a cell. Enginer kit has 48V nominal pack, which consists of 16 "cells" in series. The size of each "cell" can vary based on specific product used, it can be a single prismatic cell of 40AH ( 2kW kit ) or 80AH ( 4kW kit ) or smaller pouch type cells grouped in parallel to acheve desired AH capacity and enclosed in 2 metal boxes ( 8 "cells" each ). This is all driven by price, Enginer finds cheapest cells in the world to keep their cost low, hence many of unhappy customers ( setting aside all BMS issues, which is whole 'nother story ).

You could take 76 LiFePO4 cells instead of 16 and build a 240V+ nominal pack, this way you don't need DC booster. That is what PIS kit does and some others as well. The problem here is that you must use smaller cells, or you won't fit them in Prius. Plus, the pack quickly becomes expensive. The upside is very high efficiency ( no DC boost heat losses ), PIS easily runs at 10kW and peaks at 20kW at times. This requires good quality cells, like CALB, Winston or GBS.

So, bottom line, you have 2 technical paths to take and you get what you pay for, no miracles here.

P.S. For simplicity sake I am not talking about spoofing Prius's CAN messages to get even higher MPG, I was just responding to battery related questions.

[sipnfuel]

Originally Posted by electric1

That depends on your definition of a cell. Enginer kit has 48V nominal pack, which consists of 16 "cells" in series. The size of each "cell" can vary based on specific product used, it can be a single prismatic cell of 40AH ( 2kW kit ) or 80AH ( 4kW kit ) or smaller pouch type cells grouped in parallel to acheve desired AH capacity and enclosed in 2 metal boxes ( 8 "cells" each ). This is all driven by price, Enginer finds cheapest cells in the world to keep their cost low, hence many of unhappy customers ( setting aside all BMS issues, which is whole 'nother story ).

You could take 76 LiFePO4 cells instead of 16 and build a 240V+ nominal pack, this way you don't need DC booster. That is what PIS kit does and some others as well. The problem here is that you must use smaller cells, or you won't fit them in Prius. Plus, the pack quickly becomes expensive. The upside is very high efficiency ( no DC boost heat losses ), PIS easily runs at 10kW and peaks at 20kW at times. This requires good quality cells, like CALB, Winston or GBS.

So, bottom line, you have 2 technical paths to take and you get what you pay for, no miracles here.

P.S. For simplicity sake I am not talking about spoofing Prius's CAN messages to get even higher MPG, I was just responding to battery related questions.

Thanks for the info. It covers almost all of what I was wondering about -- specifically the use of multiple smaller capacity cells to achieve the 240 voltage without having to boost voltage, against the use of smaller number of larger capacity cells, and their respective pros and cons.

I also suppose it is much easier to balance 16 cells vs 76. Do you always need to have an even number of cells?

[Simtronic]

Originally Posted by sipnfuel

Thanks for the info. It covers almost all of what I was wondering about -- specifically the use of multiple smaller capacity cells to achieve the 240 voltage without having to boost voltage, against the use of smaller number of larger capacity cells, and their respective pros and cons.

I also suppose it is much easier to balance 16 cells vs 76. Do you always need to have an even number of cells?

You don't need to have even numbers of cells when they say balance the cells they mean all have the same SOC (state of charge) if you have one charged more than the rest it will reach full before the rest have charged properly and if you have a low cell it will be flat before the others have been fully utilized, so you see an unbalanced pack has significantly less capacity and dies earlier due to overcharged and undercharged cells. The enginer system is great for the price, but it is the cheapest by far. I think it is great they are giving a chance to many who couldn't afford to have a plug in of sorts as well as getting many more people involved.

[electric1]

Originally Posted by sipnfuel

I also suppose it is much easier to balance 16 cells vs 76. Do you always need to have an even number of cells?

Nah, it doesn't matter, its all about cost. Its cheaper to manage 16 cells than 76, since you need less BMS channels/modules. Battery quality is also all about cost, some cells are made better than others. Even best BMS can't save crappy cells from early grave.

Cell count is purely based on desired pack voltage, doesn't have to be odd or even.

[sipnfuel]

^^ Thanks for the info. I thought even was required because BMS likes to use buddy cells, but now I think this is just a method of getting 48v out of 32 cells.

[Octane]

Is there nothing special about pairing up cells in parallel versus stringing them all in series when it comes to protecting other cells from being damaged by a bad cell?

[electric1]

Originally Posted by Octane

Is there nothing special about pairing up cells in parallel versus stringing them all in series when it comes to protecting other cells from being damaged by a bad cell?

That's right, there is nothing special. Once you connect 2 or 3 or N number of cells in parallel, they become one "cell" for all intends and purposes, with capacity that is sum of all cells in parallel. BMS sees them as one cell and they cannot be managed separately anymore. For example, take 32 cells of 40AH each. You can make 32S1P pack, by connecting them all in one series string and you will end up with 96V nominal 40AH pack ( 3.8kWh energy capacity, usually rounded up to 4kW for nice round figure ). Or, you can parallel pairs of cells and end up with 16S2P config, 48V nominal 80AH pack ( same 3.8kWh of energy ). You trade voltage for current and vice versa, but pack size in kWh doesn't change. Again, you get what you pay for.

When cells die from abuse or being poor quality to begin with, they usually increase internal resistance ( IR ) up to the point of open circuit, hence contributing less and less current until zero. In 1P scenario that means the pack can't be used until bad cell is replaced. In 2P scenario this means 2nd cell in parallel to the bad one will pickup the slack, but overall pack capacity will be reduced to the "weakest link". Unfortunately, this means remaining cell will become overloaded and will die soon after, so in the long term there is very little benefit from 2P config from reliability point of view. The benefit of multi-P config is to increase pack AH size, while keeping same voltage. If DC booster is designed for 48V input, then you can achieve various pack sizes by using larger cells or pairing smaller cells, but still keeping 16 series connected "cells".

There is nothing special about Enginer's 48V pack, my guess is that DC booster design was swiped from existing 48V AC inverter, modified by removing AC stage. What would be really nice is to design DC booster with higher input voltage, like 96V or 120V, hence less conversion losses and higher efficiency. Then we could build 32S1P or 40S1P packs using 40AH cells, to keep the pack size/cost reasonably small, yet end up with more efficient system.