DIY Electric Car Forums banner

1 - 5 of 5 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter #1
Ciao This is my first post, and I ask you to help size a LiPo battery pack (like thunder-sky) that short-replace on my car.
Currently, the battery pack is composed of 18 modules Exide Dryfit Pb/Gel 55Ah connected in series for a total of 216Vdc.

The requirements of the replacement are:
1) Maintain the same range of kilometers.
2) Keep the battery charger. (Actualy have a software for charging AGM batteries from 60Ah).
3) The car has a gauge of SOC; to keep it, you must take the voltage signal to groups of 5, 5, 4, 4 batteries : 60VDC, 120Vdc, 168Vdc, 216Vdc and amper-meter in/out.
4) Insert a cell balancer.

What helps in scaling the new battery pack?

Thank you

Ciao
Fox

see me on
www.evalbum.com/2123/
and
http://www.energeticambiente.it/dis...-problemi-modifiche-batt-alternative-ecc.html


 

·
Registered
Joined
·
2,123 Posts
I would use 72 cells to approximately match 4 cells for each 12V battery being replaced.

To keep the same approximate range you could use 40AH cells ( considering that your current 55AH is a 20 hour rate, so you actually get less than that in EV ). Even with 40ah cells you should get better range considering weight reduction as result of battery swap.

So, looking at EV Components site http://www.evcomponents.com/SearchResults.asp?Cat=34

72 cells of 40ah x $44 = $3168

If space and budget allows, see if you can go to next size of 60AH, which will greatly increase your range.

To keep your charger you need to know max charging voltage and divide it by 72 and see if its between 3.6V-3.9V. If so, then you can keep your charger and adapt BMS to prevent individual cell overcharge.

Unfortunately your SOC gauge probably won't be useful, since LiFePo4 has extremely flat discharge curve. You'd have to learn how to intepret your SOC reading to adapt it to LiFePo4 voltage levels. For example, note the SOC reading when your new cells get to 2.8V-2.9V during coasting and consider that to be your new LOW CHARGE reading.

Since each lead battery is replaced by 4 LFP cells, you would connect SOC leads in 20, 20, 16, 16 pattern.

As for BMS, there are few options on the market today, pick whatever suits your needs/budget. You need to pay attention to the charger's current during final stage, to ensure it won't overrun BMS shunting/balancing capacity.

You can probably go between 70-74 cells to better match your charger's voltage, to ensure that each cell gets less than 4.0V but more than 3.6V.

Hope this helps.
 

·
Registered
Joined
·
7 Posts
Discussion Starter #3
Thanks for your reply, I put the image of the cycle of charging the battery charger siemens, and as you can see the end of charging voltage is 260Vdc (72 cells = 3.61 Vdc), which might have an optimal value.
As time you load the 40Ah and 60Ah as a charging curve as per attached image?
What kind of cell in the trade balance exist?

Ciao

Fox


see me on
www.evalbum.com/2123/
and
http://www.energeticambiente.it/disc...ative-ecc.html
 

Attachments

·
Registered
Joined
·
2,123 Posts
This charger seems perfect, it has CC and CV phases and even trickling phases which you don't need with Lithium since it doesn't have much self discharge.

Seems very similar to my Zivan NG3 charging profile, it has a timeout too.

With 72 cells you will be at 3.61V which is quite far from dangerous overcharge levels, so you will not need a fancy BMS. Some people may argue that you don't need BMS at all, as long as you manually balance your pack once in a while. This is subject of debates here and several points of view exist on this subject.

One thing is clear, your EV will work much better after this upgrade :)

I looked at your EVAlbum pictures, are all batteries easily accesible for service? If not, you should focus on centralized BMS so you don't have to service BMS modules installed on each cell. For example my BMS requires visual access to all cells, so I can see LEDs when I need to ensure proper balancing. Some BMS just run wires to each cell and have centralized display, this will probably work better for you if you choose to have BMS at all.

Hope this helps
 

·
Registered
Joined
·
7 Posts
Discussion Starter #5 (Edited)
This charger seems perfect, it has CC and CV phases and even trickling phases which you don't need with Lithium since it doesn't have much self discharge.

Seems very similar to my Zivan NG3 charging profile, it has a timeout too.

With 72 cells you will be at 3.61V which is quite far from dangerous overcharge levels, so you will not need a fancy BMS. Some people may argue that you don't need BMS at all, as long as you manually balance your pack once in a while. This is subject of debates here and several points of view exist on this subject.

One thing is clear, your EV will work much better after this upgrade :)

I looked at your EVAlbum pictures, are all batteries easily accesible for service? If not, you should focus on centralized BMS so you don't have to service BMS modules installed on each cell. For example my BMS requires visual access to all cells, so I can see LEDs when I need to ensure proper balancing. Some BMS just run wires to each cell and have centralized display, this will probably work better for you if you choose to have BMS at all.

Hope this helps

Hello Dimitri, thanks for the information ...
You know I live 30km from a Poviglio (Reggio Emilia) where to build the Zivan battery charger ...
Ok if the battery charger is ok as models and brands of balancing battery you used?

I look your system is 128Vdc for (i think) 20Amp. = 2560W for recharge the battery for 10hour...that absorbs power from the line ac?

Thank you

Ciao

Fox



see me on
www.evalbum.com/2123/
and
http://www.energeticambiente.it/disc...ative-ecc.html
 
1 - 5 of 5 Posts
Top