I bought a MultiPlus II, 48v, 5000va, 70a (120v) last year. Now ready to commission. Long story short: my well is 500 feet deep, so I need a 1hp / 230v pump. Therefore I bought a Victron AutoTransformer (120/240 | 32). My well pump supplier is telling me my pump will generate a 6500 start-up surge.
Will the MultiPlus II 48v | 5000va | 70a (120v) be able to handle that?
Thanks!!
I don’t think this will work under any circumstances and the Multi will go into ‘overload’ and switch off.
But you could install a soft starter. These are available for little money. Here you regulate the starting ramp of the current for 2 phases … This is usually sufficient, as you don’t have a heavy-duty Load. It will probably be a multistage pump.
If that doesn’t work, it will probably have to be a much more expensive frequency inverter.
Both solutions are definitely better for the Multi and the pump. Both are relieved in the starting moment…
6500 W is the startup surge, so LRA (locked rotor current) is 27.1 A (6500W/240V).
You should verify that number with the well pump supplier.
I assume that the autotransformer is creating 240V by up-converting from 120V.
You can only use 28A continuously into the neutral on the AT, which will be 14A continuous at 240V. Which is probably fine for continuous use of your pump.
However, you will need 54.2A at 120V for 1-2 seconds when the pump starts up.
Although this greatly exceeds the allowable neutral current on the AT, it is so short that it will probably work. But definitely something to be aware of.
The Multiplus-II 48/5000-70 120V has peak surge power of 9000 W.
Therefore, I believe it will handle the surge when the pump starts, though it probably will dim the lights badly. And you have no room for other loads simultaneously, which is a great inconvenience. Make sure you have sufficient battery capacity and thick enough cables because that is a huge hunk of power.
Here is some info on overloading and peak power.
The takeaway here is that the inverter will do 150% of rating for 5 seconds, which is 6000W.
If the pump does not start up in 5 seconds, the inverter will shut down.
Adding a soft-start to well pumps is not trivial, and depends on whether it is three-wire or a two-wire pump. The three-wire pumps have a control box.
To follow what Rick said, I think you’re going to ultimately be unhappy with this setup. You can try using the AT 100A and see if it will be sufficient, but it will heat up quite quickly after just a few minutes of running your well pump and if it does, it will shut down.
I suggest you get a second 48/5000 along with the AT 100A, configure the multis for split-phase, and then you’ll be happy. If you choose to try the AT 100A, no problem, and then if you decide that you will need the second 48/5000 you won’t have wasted any money. Just some time to rewire. Good luck with your project.
Sadly, I already purchased the Multiplus II and the AutoTransformer. Woe is me! If I had it to do all over again, I would have purchased a system already set-up on a frame, solar and all–much less headaches for a newbie.
I couldn’t find a consultant to design the system for me. I’ve found the solar industry to be willing to sell, but not willing to help, in spite of the promises of nearly every website. I bought the bulk of my system from a national supplier here in the US, but I didn’t buy every single piece from them - so they declined to help review my system design.
BUT, I have found this forum to be a very helpful, as well as DIYSolarForum.com
Anyone have a recommendation on where I may sell my two small Multiplus II and AutoTransformer?
Thanks 
I don’t think you need to sell them. I think you just need a second MultiPlus-II 48/5000 and then you’ll be good.
There are companies out there that will spend more time with DIYers. And there are companies who sell every brand under the sun and get it to you in two days, but won’t spend time with you beyond the sale. Both add value, but in very different ways.
You are right–both add value along the way. I had some dinner so I feel less grumpy!
Will heed your advice and keep what I have.
I did contact the well driller/pump provider/installer. They do have soft starts for well pumps. He recommended the Goulds 1AS15 variable speed pump. Will see if that will help while reading up on using two inverters…
Thank you again!
