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I'm making a power board for my robot and I am looking for some advice regarding LiPo battery protection ICs.

I might need to draw a fair bit of current (9A), though if I get the programming right, it shouldn't be a problem (will probably be around 3A max).

Anyway, I was looking at using DS2764 from Maxim (datasheet), and it seems nice aside from the fact that I don't think I can use the 14.7V packs (need 12V output) I wanted to get :) Plus the current is limited to 2.5A. It also has the 2-Wire Interface that I don't plan using, so it's a bit of a waste.

Next, I started looking on Digikey for some LiPo protection devices, and now I'm confused: let's say I have a 14.7V LiPo battery, which means it's 4S I think. So technically there are 4 cells in there, but I don't have access to all 4. So when sorting the ICs, should I look for ones that say 1 cell (because that's the number of connections I have) or 4 cell? The 4 cell ones seem to always want inputs from all 4 cells...

Do you have any suggestions for something that can handle the current (I'm using a fuse anyways, so just as long as it has a fairly high limit it's probably ok) and the voltage? I know it's quite vague, but I don't really know where to look.

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An important question to ask yourself: Can I really not access the cells' individual wires?

Your best option is accessing the wires to all the cells, usually battery packs have balancing connectors, with in it wires to connect to the joints of each set of cells.

This is done, because LiPo cells are much more sensitive to cell-to-cell imbalance and will waste away much faster if you do not check the cell balancing regularly, preferably each time you charge and/or discharge. Alternatively you also should make sure no single cell ever discharges below a level of about 2.5V.

The 4 cell chips do all of that for you, if you choose an appropriate one. They will stop current flow when any one of the cells is depleted, in stead of when the entire pack reaches a lower limit, and they should be chosen to have some balancing feature, to alow you to fully charge all the cells.

A 1 cell device will only work with one single cell, because it expects the upper limit of 4.25V and lower limit of 2.5V, connecting a full pack of 4 cells to its terminals will at best just not work, but most likely turn it into a ball of smoke.

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  • \$\begingroup\$ Ok thanks! So if I'm looking at this IC, I don't see any information about the current it will source through it? Is that irrelevant? \$\endgroup\$ – Mewa Oct 5 '14 at 18:48
  • \$\begingroup\$ @Mewa that's because that chip is intended for a battery pack with added intelligence, they intend the Gas Gauge IC to control the chip and set the parameters. You can see in the tables that the "V(OL)", or "Overload Trip Voltage" can go from 25mV to 250mV depending on settings and configuration through the I2C port. Combine that trip voltage with a set resistance and that will dictate the trip-current. E.g. with 50mV and 10mOhm it would be about 5A. Same resistor, but 100mV, it's about 10A. The GG can adjust to the battery's level of charge. Do take care with the external MOSTs though \$\endgroup\$ – Asmyldof Oct 5 '14 at 20:00
  • \$\begingroup\$ Asmyldof, thanks for your help! What about a chip such as this? I can see you can connect them in series and that would work for my purpose I think. But I don't see anything similar to the overload trip voltage here, so again I'm not sure how to find out what current will trip it. Maybe it doesn't have overcurrent protection? \$\endgroup\$ – Mewa Oct 9 '14 at 22:32
  • \$\begingroup\$ @Mewa if you build figure 16 or 17 that would work. For the voltage levels it checks for see table 2 on page 4. I'd suggest a BAH or BAI type (BAH for fig 16, BAI for fig 17 with discharge balancing as well) \$\endgroup\$ – Asmyldof Oct 10 '14 at 0:32

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