[RE-wrenches] DC-DC converter for SQFlex

[Gary Higbee]

Hi Wrenches,

I’m assisting a customer and well person in replacing a failed Lorentz ETApump (after 15 years of intermittent use). We’re looking for a quality DC-DC converter to power a not-yet- ordered Grundfos SQFlex 6 SQF-3 from a 24 V Surrette battery bank (wish it was 48!). The pump draws a max of 8.4A and the curves say we’ll need about 600 watts so I figure we’d want at least 70 volts out. Ideal would be a higher DC output, say 200V (save a couple hundred feet of larger copper, greater efficiency) and at least 3A (see questions).

The primary power source will be 240V AC but my customer wants a fallback for battery operation. We plan to use the Grundfos IO 101 SQFlex switch box, which will switch to DC if the AC fails. Also the CU 200 SQFlex control unit, so we can accommodate the existing float switch up the hill, etc.

The Grundfos tech person I spoke with today said the DC system should be able to supply 8.4A, regardless of the DC voltage.The pump curve says we need 600W for maximum performance at the lift we’ve got. It seems to me that if we’ve got 200V and need 600W we’d be drawing 3A. Yet if the Grundfos factory line is there should be 8.4A available that’s 1680W. The tech guy said he didn’t have specific information why we’d need 8.4A regardless of pump input voltage. 

The Grundfos Product Guide says:

Max. ratings are as follows:
• Maximum power input (P1) of 1400 W
• maximum current of 8.4 A
• maximum speed of 3600 rpm (think I read somewhere it’s 3000 rpm for this helical rotor model)

The pump delivers its maximum performance when one of the above parameters is reached.

Two questions:

1) Do any of you have experience running the SQFlex on DC, and what to make of the 8.4A at any input voltage factory recommendation? Maybe basic amps/volts/power calculations aren’t applicable given the pump electronics?

2) Are you aware of any DC-DC converters that will get us from a nominal 24V battery bank to 200V, or somewhere between 70 and 200V, with an appropriate current limiting amp rating to get us at least 600W (depending on thoughts regarding the above question)?


Thank you,

Gary

Gary Higbee
Windstream Solar
Oregon License 17LRT
Renewable Energy Consulting
gary at windstreamsolar.com <mailto:gary at windstreamsolar.com>
541-954-3881
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