Astro Charger as a Power Supply

This message from "Jim Keller" <jkeller1@peoplepc.com> brought to you by EFLIGHT!

The Astro 110D charger has a "Test" mode that allows
one to provide a constant DC voltage via the current
adjust knob. I've used this mode to power brushed
motors at low voltages for break-in. Therefore, the
110D can be used as a power supply (yes, I know you
need another power supply to power it - just bear with
me here). Since it can charge up to 18 NiCd cells, it
must be capable of around 22 volts.

But here's my question. If you need around 18 vdc to
charge a 3 cell LiPo pack using a multi-cell LiPo
charger, and you only have a 12 (or 13.6) vdc power
supply, can the Astro charger be used for this purpose?
Perhaps Doug Ingraham can address this.

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This message from Doug Ingraham <dpi@rapidnet.com> brought to you by EFLIGHT!

On Mon, 1 Dec 2003, Jim Keller wrote:

> This message from "Jim Keller" <jkeller1@peoplepc.com> brought to you by EFLIGHT!
>
> The Astro 110D charger has a "Test" mode that allows
> one to provide a constant DC voltage via the current
> adjust knob. I've used this mode to power brushed
> motors at low voltages for break-in. Therefore, the
> 110D can be used as a power supply (yes, I know you
> need another power supply to power it - just bear with
> me here). Since it can charge up to 18 NiCd cells, it
> must be capable of around 22 volts.
>
> But here's my question. If you need around 18 vdc to
> charge a 3 cell LiPo pack using a multi-cell LiPo
> charger, and you only have a 12 (or 13.6) vdc power
> supply, can the Astro charger be used for this purpose?
> Perhaps Doug Ingraham can address this.

The 110D 110DX 112D 112DX and the new 109 all have voltage boost
circuitry. The 109 and 110 series can boost to about 30 volts. The 112
can boost to as much at 80 volts. When boosting the input current will be
higher than the output current because watts in must equal watts out. If
the charger was perfect efficiency with a 12 volt input and a 24 volts
output the input current would be twice the output current. Since the
charger is something over 90% efficiency the input current will be a bit
higher than twice the output current in this case.

Without modification it would be a bad idea to try to use the 110D charger
to boost the 12 volts input to 18 volts to feed another charger. This is
because the charger controls current, not voltage as configured. Small
changes in load will dramatically change the output voltage. You would
need to change the feedback loop so that the charger was a constant
voltage output rather than a constant current.

Doug Ingraham
Rapid City, SD USA




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This message from Doug Ingraham <dpi@rapidnet.com> brought to you by EFLIGHT!

On Mon, 1 Dec 2003, Jim Keller wrote:

> The Astro 110D charger has a "Test" mode that allows
> one to provide a constant DC voltage via the current
> adjust knob. I've used this mode to power brushed
> motors at low voltages for break-in. Therefore, the
> 110D can be used as a power supply (yes, I know you
> need another power supply to power it - just bear with
> me here). Since it can charge up to 18 NiCd cells, it
> must be capable of around 22 volts.
>
> But here's my question. If you need around 18 vdc to
> charge a 3 cell LiPo pack using a multi-cell LiPo
> charger, and you only have a 12 (or 13.6) vdc power
> supply, can the Astro charger be used for this purpose?
> Perhaps Doug Ingraham can address this.

I should have pointed out that you only need a little over 12.6 volts to
charge a 3S pack. You need a little over 16.8 to charge a 4 cell pack.

Doug Ingraham
Rapid City, SD USA




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