Can I use a Victron MPPT to regulate charge a DC water heating element without batteries?

DIY
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Can I use a Victron MPP to regulate charge a DC water heating element without batteries?

I’m not charging batteries, solely using a resistive load (DC water heating element), freestanding- not connected to the grid.

Presumably I need an MPPT designed for a direct DC load control?

As I understand it an MPPT will be more efficient as opposed to charging the element direct from the panels.

I have;

2 x JA Solar JAM66S30

Values for these 505W panels:
• Vmp (voltage at max power): ~38.5V
• Voc (open-circuit voltage): ~45.8V
• Imp (current at max power): ~13.1A

I’ll probably buy a 3rd panel.

I directly wired the two 505W panels to a 48V 1000W heating element.
I tried series and parallel, read some advice somewhere and went for parallel, which may well have been another mistake.

The element has an integrated thermostat.

It turned out to be a mismatch. In parallel the element only ran at
36.78V
14.26A
524W

Naïvely I was expecting 1000W which would have been happy days, off we go. After about a weeks use the element went pop and gave up. Now that did surprise me as I thought it was under stressed. It was rated at 2.5 ohm’s but by my calcs it was running at about 2.9 ohms. Anyway it’s toast , which is a good thing because it wouldn’t have enough grunt to heat 200ltrs. So up with the volts, down with the amps, I’ve ordered a 96v 1000W and a 96v 1500W with thermostats. ( with delivery and special offer it was better to get 2 in case I burn out another).

The plan is;

3 Panels in Series
• Vmp total: 38.5V × 3 = 115.5V
• Voc total: 45.8V × 3 = 137.4V
• Power: ~1515W

What could possibly go wrong?

Would I be better off with an MPPT ( a 150/35 or 45 or even 60)?
Would I need a DC load relay?

Thanks for any help.

Once this is sorted the plan is to get a separate system with batteries because they’ve suddenly taken to cutting the power for the whole country here in Spain. One thing at a time though.

2

Don’t know what happened to the T in MPPT. Perhaps the moderators can put that right.

3

It’s not recommended to use an MPPT without battery.
If you use that MPPT only for the heating element, use some small and cheap (AGM) battery to have it as a buffer.
Something like 4 x 12V/5A, like the ones in UPSes, connected in series.
Of course, set proper bulk/absorption/float voltages in order to prolong as much as possible the batteries life.
A DC (solid state, if possible) relay for the heating element is always a good thing, because you can control much better the system, especially when you are out of sun, in order to not let the batteries discharge excessively… :wink:
But the battery must be there uninterrupted on the output of the MPPT.

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Connect the panels directly to the heating Element, nothing can happen if the element can take more power then the panels can supply.

5

That too, but only if the panels power is less than heating element power and panel voltage is the same (or less) as the heating element.
In other words, match the panel power AND voltage with the heating element’s. Otherwise a lot of power will be wasted.
If he plans to expand the panel power, it’s always good to have a constant in the system and that’s the MPPT output voltage and therefore the heating element voltage.

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Yeah, but he ordered a 96v element…