Booster pump on 8kW inverter

[Scubadude]

Hi all,

Spent my lunchtime at three pump shops across the street, looking for a backup water system. I am happy with a 2000-2500 L tank and 1.1kW booster pump. Question is, two of the three suggested VSD pumps instead of a standard DOL pump because I have solar.  I understand about inrush current, but surely 8kW of inverter and 200A of battery supply will easily cope with this? Price difference is R2500 for standard vs R12000 for VSD pump. Is this additional cost 1) warranted and 2) neccesary? 

[Jacques Ester]

I am running an .75kw pressure pump of my 5kw inverter with no issues. I assume if you have a large load on the inverter and the pump starts that will be an issue.

[Scubadude]

Thanks Jacques. I was thinking the same. What about guys that had booster pumps long before they went solar?

[Basil Katakuzinos]

Have a +- 1KW DAB Easybox diver, works fine on my MPII even when large loads are running also.

 

I am not super educated in the realm of pumps but I would imagine a VSD would be better for solar/Offgrid because it is not drawing the full 1kw whenever it is running.

[P1000]

12 minutes ago, Basil Katakuzinos said:

Have a +- 1KW DAB Easybox diver, works fine on my MPII even when large loads are running also.

The Esybox has a built-in VFD, I suspect that's the "R12000" option OP is referring to... It's much more than just a VFD pump, though, and IMO worth the additional expense.

Edited April 20, 2023 by P1000

[Robbo]

For your use case as just a water backup system, a standard DOL pump may work. You will have to carefully manage your loads during loadshedding to be sure not to trip the inverter though.

I went with the bigger Esybox VSD and I'm very glad I did for my offgrid water solution. You would not believe how many times the pump turns on per day, it must be hundreds. So its useful that its just 150W-500W at a time in most cases. Only if a few taps go on at a time will it get closer to full power.

So you would need to consider that there will be a full spike in power every single time someone fills a glass of water or washes their hands when getting the DOL pump. 

[BTTB]

On my 11KW Inverter with 3 x 5.5 AM2 which is slightly bigger than your system I can run 2 well point pumps at around 0.8KW each and one Booster Pump @ 1.5KW and everything else in the house. Bascially, all excluding the Geyser, Stove, Tumble Dryer and Jacuzzi., Pumps are for the extended garden. 
No solar as yet.

This arrangement can run for 2 hours easily, if it's a 4-hour load shed, then I try not to use any of the pumps, just the house, plugs, kettle, washing machine and lights etc, otherwise it flattens the batteries to 20% and below. 

Edited April 20, 2023 by BTTB

[Chris Louw]

@ScubadudeWhy do you want a 1.1kw pump. I Use a 0.37kw pressure pump for a backup with no problems.You can buy them for R1399 at Adendorff Machinery. This includes the Flow control switch. 

[GreenFields]

I'm using a 0.37kW pump for backup, but flow rate after filters and pipe friction isn't great. Wouldn't recommend for it multi-storey homes, larger homes, or for running more than one or maybe two taps at a time.

Looking at the VSD type, if it's really just for home and for backup, the performance difference between the 0.75kW VSD and the 1.5kW VSD I don't think is worth the difference in price. It jumps from R7000 to R12000 for maybe a 10% improvement in performance in terms of flow rate and pressure.

Otherwise maybe consider if a combination of DOL pump and pressure tank will resolve the issue of constant switching on and off, at maybe half the price of the 1.5kW VSD.

[Scubadude]

6 hours ago, Chris Louw said:

@ScubadudeWhy do you want a 1.1kw pump. I Use a 0.37kw pressure pump for a backup with no problems.You can buy them for R1399 at Adendorff Machinery. This includes the Flow control switch. 

I have a single story house but a large family - when my wife and kids get home late afternoon it is not uncommon for 2 showers  and 2 baths / 3 showers and 1 bath to run at the same time. Maybe I can get away with a 0.75kW but I think 0.37kW may be a little light 

Edited April 20, 2023 by Scubadude

[TimCam]

9 minutes ago, Scubadude said:

I have a single story house but a large family - when my wife and kids get hom late afternoon it is not uncommon for 2 showers  and 2 baths / 3 showers and 1 bath to run at the same time. Maybe I can get away with a 0.75kW but I think 0.37kW may be a little light 

An 8kW inverter will handle a 1.1 kW pump start-up, but as you suggested try the 0.75 kW pump. Most important for flow and head is pipe diameter feeding the pump, as you don't want cavitation. Unfortunately most houses have 15mm copper pipe throughout except feed in, so nothing much you can do there.

I currently have a 0.55 kW booster pump, but we rarely have more than 2 taps open at a time. When my water purification room is complete, I'll be running a 0.75 kW pressure pump and a 0.55 kW booster pump in tandem at times, plus another 0.55 kW booster pump for the green house. I also "only" have a 8.8 kW inverter.

[frivan]

6 hours ago, Scubadude said:

I have a single story house but a large family - when my wife and kids get home late afternoon it is not uncommon for 2 showers  and 2 baths / 3 showers and 1 bath to run at the same time. Maybe I can get away with a 0.75kW but I think 0.37kW may be a little light 

My 0.37kW pump worked for one shower but you noticed the reduced flow when filling the bathtub. Although I saw this as a feature, I upgraded to a 0.75kW VSD pump to better regulate pressure to my RO system. Now I don't notice any difference between backup water and municipal water... other than backup water being more reliable. My house runs on a 5kW inverter.