Danfoss solar PV inverter gaff!!?? - Page 1
Forum section: electronics / general

author: unknownparticle
author_rank: Frequent Contributor
timestamp: January 07, 2020, 02:20:18 pm
content: Recently I bought a new Danfoss solar inverter at a clearance price, type DLX 3.8. It is a high end product and extremely well made but I think I may have shot myself in the foot! There is an aspect of the spec that I wasn't aware of, the input threshold, or, turn on voltage! That is specified at 230 VDC.My plan was to install a SPV system in stages, starting with 1KW, then eventually increase to the max inverter rating of 3.8KW. Problem is, depending on the loaded output voltage of the panels I use, it seems that I'll need at least 8 panels to reach the inverter switch on voltage. Is this correct or am I missing something? Are all inverters like this?

author: Kilrah
author_rank: Unknown
timestamp: January 07, 2020, 02:36:57 pm
content: Yup, looks like it needs the input to be within 230 and 500V.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 07, 2020, 05:03:58 pm
content: Quote from: unknownparticle on January 07, 2020, 02:20:18 pmSad, nice inverter with transformer so IMOP safer, you could use 72 cell panels to gain a little voltage but you still need quite a few, in theory you might get away with 6 but knowing perniticy inverters maybe you need 7 so much the same as 8x60 cell jobs.I have an IG15 and it's a bit more forgiving on the low end (170V cut-in) but it takes two transformer taps to do it (cover the full range to 500V).

author: Kilrah
author_rank: Unknown
timestamp: January 07, 2020, 05:13:21 pm
content: Maybe get smaller panels, so instead of adding more in series over time you make a string that's long enough form the start but add parallel branches over time?

author: unknownparticle
author_rank: Frequent Contributor
timestamp: January 07, 2020, 05:19:40 pm
content: Quote from: fourtytwo42 on January 07, 2020, 05:03:58 pmThanks for that. Excuse my ignorance, I'm new to SPV, so could you explain where transformers come into this please?

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 07, 2020, 06:05:38 pm
content: Quote from: unknownparticle on January 07, 2020, 05:19:40 pmTraditionally in an GTI the transformer was used to isolate the DC side (panels) from the AC (grid) side of the inverter meaning for example the panels could be grounded. Someone had the bright idea that as the transformer was only 98% efficient the efficiency could be improved by eliminating it and connecting the panels directly to the grid, this was the marketing speak, the actual reason was to save the manufacturing cost of the transformer!As I said before IMOP these "transformer-less" inverters are dangerous, how they ever became approved for use god alone knows, it's like having an electric kettle with a bare wire heating element because its supposedly more efficient

author: unknownparticle
author_rank: Frequent Contributor
timestamp: January 07, 2020, 06:28:35 pm
content: Ah, I see!! JHC, as you say, how did they get approved without isolation??!!So it seems I'll be installing a larger system than I planned originally! What are the current best panels to go for? This is the UK BTW.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 07, 2020, 06:40:52 pm
content: Panels for DIY are not easy to find in the UK at a reasonable price, there are a few companies around selling them for silly money but of course the worst problem is transport, there big buggers, two men standing side by side and I don't think they would stand up to a roof rack! Fortunately I have a nice neighbor with a big van. Ebay is probably as good a place as any to start as you want to figure out the going rate of pence/watt (anything approaching £/watt or over is way overpriced), you will also get an idea of what panel sizes, watts, cells, voltages & powers are available, try and stick to the most popular. For example there are fancy 300+W 60 cell panels but the norm is around 260W. Particularly bear in mind you may be back for more to extend your system and if you can get the same again so much the better. The most hopeless source for anything is your local PV installer, there just not interested, it's also not a good idea to buy 2nd-hand stuff that's been de-installed (IMOP). Happy hunting

author: unknownparticle
author_rank: Frequent Contributor
timestamp: January 07, 2020, 06:56:29 pm
content: Typical, the good 'ol UK strikes again! Thanks for your help, appreciated.

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 08, 2020, 02:49:54 am
content: Quote from: fourtytwo42 on January 07, 2020, 06:05:38 pmHaving worked on a few of those systems, isolation doesn't really make a high voltage solar array much safer. A ground fault would cause the inverter to isolate the input anyways. An older isolated inverter without ground fault protection will allow a ground fault to become an undetected fault, possibly allowing that fault to turn into an arc fault if it degrades further.