The alternators of the hybrid drive train I'm making will be using a voltage and amperage that is not very common (48V @ 145-155 A). As a result, it is difficult to find a charger which I can use in this system (since most chargers are meant to be powered from the electricity grid (so 230V or 110 V). Also, most chargers do not allow the batteries to be charged at the highest C-rate they can sustain. To resolve this, I hereby put up a post to let us solve this (and hopefully generate a solution that will benefit, not just me, but anyoone building an electric vehicle that uses unconventional voltages/amperages or batteries).
An obvious solution is that we just describe the procedure on how to create (a very simple) electric charging circuit, from scratch.
First off, here are the details of my electric vehicle system, which can serve as an example:
* the batteries I use are 4 NiFePo4 batteries of 12V, with 2,5Ah which I wired in series to make one 48V battery. I use two of these intermittently, but that's not important here. The C-rate of the batteries is 4C
* the input power is (as allready mentioned above), 48V @ 145 to 155 A
Let's start with calculating out some things based on the variables we allready know.
We know that:
* They're NiFePo4 batteries. The nominal voltage of NiFePo4 cells is 3,2V. Since we know the nominal voltage, we also know how much cells there are in the 12V battery. This is 4, since 3,2 x 4 = 12,8 V. So, it's a "4S pack". We don't know how many P's it has but that's not important. We also know the maximum charge rate with this, since the maximum charge voltage at which to charge LiFePo4 batteries is 3,6V per cell; since we have 4 cells, the maximum charge voltage is 14,4V for these 12V batteries.
* We know the C-rate of the 12V batteries is 4C, and the capacity is 2,5 Ah. So 1C= 2,5 and we have not 1 but 4 C, so maximum discharge rate is 10A (2,5A x 4). Charge rate would be a little less, but near that amount.
The charge curves for NiFePo4 tell us that we best charge them:
- from 10 to 90% of State of Charge (SOC) at the full C-rate the batteries can handle (in our case 4C or hence 10A)
- from 90% to 100% of State of Charge (SOC), at 0,5C (or hence 1,25 A)
So ideally, in my example, I'd need to make a charging circuit that is able to charge 4 NiFePo4 batteries of 12,8V from a 145A @ 48V input stream. The rate at which to charge the batteries would be 10 A @ 14,4 V for 10-90% of SOC, and 1,25 A @ 14,4 V for 90%-100% of SOC
How would I make such a circuit in practice ?
Also, I'll only be using a small part of the power (more precisely, the surplus power will be: 145 A @ 48 V - 10 A @ 14,4 V = 6960 watt - 144 watt = 6816 watt ). So where does this power go in such a charge circuit ? Is it normally just grounded ?
The above calculations can obviously be done for any type of battery (LiPo, NiCd, ...) -regardless of their C-rate- and for any other input stream. We just need to specify now how one can make the charge circuit in practice.
An obvious solution is that we just describe the procedure on how to create (a very simple) electric charging circuit, from scratch.
First off, here are the details of my electric vehicle system, which can serve as an example:
* the batteries I use are 4 NiFePo4 batteries of 12V, with 2,5Ah which I wired in series to make one 48V battery. I use two of these intermittently, but that's not important here. The C-rate of the batteries is 4C
* the input power is (as allready mentioned above), 48V @ 145 to 155 A
Let's start with calculating out some things based on the variables we allready know.
We know that:
* They're NiFePo4 batteries. The nominal voltage of NiFePo4 cells is 3,2V. Since we know the nominal voltage, we also know how much cells there are in the 12V battery. This is 4, since 3,2 x 4 = 12,8 V. So, it's a "4S pack". We don't know how many P's it has but that's not important. We also know the maximum charge rate with this, since the maximum charge voltage at which to charge LiFePo4 batteries is 3,6V per cell; since we have 4 cells, the maximum charge voltage is 14,4V for these 12V batteries.
* We know the C-rate of the 12V batteries is 4C, and the capacity is 2,5 Ah. So 1C= 2,5 and we have not 1 but 4 C, so maximum discharge rate is 10A (2,5A x 4). Charge rate would be a little less, but near that amount.
The charge curves for NiFePo4 tell us that we best charge them:
- from 10 to 90% of State of Charge (SOC) at the full C-rate the batteries can handle (in our case 4C or hence 10A)
- from 90% to 100% of State of Charge (SOC), at 0,5C (or hence 1,25 A)
So ideally, in my example, I'd need to make a charging circuit that is able to charge 4 NiFePo4 batteries of 12,8V from a 145A @ 48V input stream. The rate at which to charge the batteries would be 10 A @ 14,4 V for 10-90% of SOC, and 1,25 A @ 14,4 V for 90%-100% of SOC
How would I make such a circuit in practice ?
Also, I'll only be using a small part of the power (more precisely, the surplus power will be: 145 A @ 48 V - 10 A @ 14,4 V = 6960 watt - 144 watt = 6816 watt ). So where does this power go in such a charge circuit ? Is it normally just grounded ?
The above calculations can obviously be done for any type of battery (LiPo, NiCd, ...) -regardless of their C-rate- and for any other input stream. We just need to specify now how one can make the charge circuit in practice.