Power Shield – charge current for LiPos with < 500mah?

Hardware
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The Power Shield v0.2.1 specs state a charge current of 500mA via USB, and 1A via DC.

A common guideline for ‘garden-variety’, 1C charge-rate LiPos is to charge them at a maximum rate based off their capacity rating (i.e. a 1C LiPo @ 500mah can be charged at a rate of 500mA safely).

With the Power Shield’s set charge rates (0.5A USB, 1A DC), does that mean LiPos rated below 500mAH/1AH should not be used?

There are high quality LiPos targeted at the RC hobbyist that typically allow 5-6C charge rates. But I’m curious as to the use of affordable, 1C charge-rate LiPos out there that are under 500mAH.

p.s. I also checked the Power Shield’s BQ24030 datasheet, and reckon that the charge rates set during the design of the board are very sensible limits. I just need some clarification towards the safety aspects of using lower-capacity LiPos w/ the Power Shield.

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…and I noticed that the Power Shields are no longer available for sale at the Particle Store.

Any plans to manufacture them again?

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@steph can comment about the availability.

As for the charging current, You can cut off the trace for ISET2 and ground it (but it’s super hard with such a small pad) to default the charging current to 100mA.

You will have to be careful to use a minimum 500mAh, 1C Lipo-battery since that’s the minimum charging current set.

I have opened up an issue here: https://github.com/spark/docs/issues/212

1 Like
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Thanks @kennethlimcp

You meant grounding ISET2 will set a charge of 100mA, and not 1A, right? :wink:

Yes they're small, but their position's thankfully in a convenient spot!

The documentation for the I2, PSEL and CE jumper pads should be included in the Power Shield docs, though.

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ok updated the typo :wink:

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Hi @chuank,

Power Shields are temporarily unavailable due to complications around shipping lithium polymer batteries. We are sorting it out though and will have them back up!

2 Likes
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Typically, for best battery life (on normal packs) it’s recommended to not exceed 0.8C. See http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

eg, before the chemistry got all complex and leading edge on the iPhone, we did not exceed 0.7C for the CC phase. Charging faster shortens pack life.

Some other notes:

  • charging at full CC rate below 15C can cause issues with copper plating (as I remember) so reduce the charge current (0.1C, 0.2C).
  • do not charge AT ALL below 0C or above 45C at the pack. Most charge chips enforce this with an attached thermistor.
  • avoid any DISCHARGE above 60C (again, varies per vendor). This is why iPhones shut down at high temp, it’s a pack safety issue.
1 Like
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@heather, how about an option to sell Power Shields sans 2AH LiPo battery? I’m sure the community will be able to source locally for the batteries.

May I suggest the importance of warning the user not to use <500mAH / 1AH LiPos with the Power Shield (and from @hfiennes’ 0.8C recommendation, perhaps <600mAH / 1.2AH?) This can be clearly included in the store’s product description/datasheet, and packaging in the form of a safety label.

…and as a suggestion, perhaps the next iteration of the Power Shield can include selectable charge rates for the BQ24030 through additional jumper pads? It might be a risky option for beginners to LiPos, but then again who’s to stop owners of v0.2.1 Power Shields now from plugging in 200mAH LiPos and having them swell up (and hopefully not blow up)?

Thanks @hfiennes for the additional details, this is very helpful information on managing LiPos. Good to know that 0.8C’s the best-practice recommendation for normal packs.

The Power Shield’s a great design with a compact footprint (the lack of mounting holes is my only grumble), so I’m looking forward to seeing it available again.