Installing a 6 kW 48 V rectifier rack in the basement

We put up, populate, wire and load test a 25 year old Powec 48 V rectifier rack! Including batteries, breakers and a 50+ year old trash picked cable to hook it to the main 48 V bus!
6 kW passively cooled? No problem! Despite dating from 1997, the oldest modules (PMP 1.48) are over 84 % efficient, and the newest ones (PMP 13.48) are over 89 % efficient - not bad!
Throw money at me: / ffcossag
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[@Lillfot]

As always, envious and inspired by your shenanigans. Keep on keeping on, brother!

[@FFcossag]

Thanks, will do!

[@daskasspatzle2396]

The old telecom stuff was nice :-)

[@twocvbloke]

In the event of a power failure like that long-lasting one, the heat from the cables alone ought to keep you warm throughout... :P

[@FFcossag]

Hehe, yeah, at 120 A, the entire length of cable between the rack and the DC central will dissipate about 60 W. Ideally, it should never have to do that since it's mostly just an AUX battery hookup, but you never know!

[@tigerelectronics5966]

Absolutely beautiful! 👍

[@FFcossag]

Thank you! Cheers!

[@tigerelectronics5966]

@@FFcossag :D Now you can charge properly from the grid too! Using that salvaged cable with the shield was a wonderful idea, I might use that idea myself for my own DC power stuff :) I never thought about using those cables for it, I have access to plenty of them (3x25+16) but never realised they could be useful for this. Ialways assumed the shield resistance would just be too high so I never attempted to try them, after watching this I realised it might not be so bad afterall :D Free stuff is the best :)

[@FFcossag]

Free stuff is indeed the best, and 3x25+16 is fine for up to 150 A or so if you do 2x25 +1x25/1x16! I was meditating on these cables with a friend, and they might actually be fine for a little bit more than that, since the large surface area of the shield, being wrapped around the outside of the entire cable, might allow it to cool off better than the internal conductors - but I wouldn't risk more than 150 A anyway, hehe.

[@tigerelectronics5966]

@@FFcossag Hehe, cable lenght also plays a important role, so for a short run, it might actually be safe to run even more powah through it :) But yes indeed, I suspect the shield might be able to handle more than one would think too, I might need to bring out my big boy transformer and do a little test on this :wink:

[@FFcossag]

No, you won't be able to run more current through it than that. Those cable current specs are calculated based on how much power a cable can realistically dissipate per unit length without overheating. While you will have less of a voltage drop problem for a shorter cable, the only way to get higher current ratings for a specific cable thickness is to use higher-temperature insulators. A teflon cable will have a higher current rating than a PVC cable, for instance, since it can handle higher temperatures without melting.

[@MindMeetMaker]

Do you have any extraction in that space for any off gassing from all the lead acid batteries? Genuine comment love following your DC battery power updates 👍

[@FFcossag]

Yes! This space used to house an oil furnace, so there's a HUGE chimney hookup that provides completely overkill ventilation without even needing any fans. I don't know exactly how much air it moves, but if I hold a normal 120 mmPC fan in the chimney hookup, it'll turn a good 300 RPM just from the passive flow. There's a roughly 80x80 cm air filter installed in a window frame in the adjecent room, so the space is constantly fed with fresh, clean air.

[@MindMeetMaker]

@@FFcossag I knew you would have it covered, not sure I heard you mention it in a video probably did but I probably missed it, anyway thanks for the power updates I always like the long explainations a testing, Im a telecoms engineer so its nice when I recognise some old -48v equipment 😁👍

[@FFcossag]

I actually don't think I've mentioned it! It's been such a passive thing that I've just kind of not thought about it.

[@thomaselli01]

Would be interesting to know how much heat the systems are dissipating. Do you have a thermometer in the basement?

[@FFcossag]

The MPI dissipates about 200 W 24/7, add another 7 % of the total load power to that if it's running off of batteries and 1 % in grid mode. The 48 V charger in the video is 84-89 % efficient depending on which modules I use. I'm currently drawing about 1.6 kW out of the Powec rack, and it's putting out about 350-400 W of heat doing that. The heat pump also puts out a fair bit, but I don't know how much. Since the space is fairly well ventilated, the temperature at this time of year stays around 10-15 C.

[@thomaselli01]

@@FFcossag too bad the ventilation loses all the heat. A ventilation system with heat exchanger would make good use of all the exces system heat to warm the basement or other room 😁

[@SuperBrainAK]

wow that thing is cool!! how exactly are you dealing with the positive ground issue? is there anything else grounding your 48v DC system? inverter, loads etc?

[@FFcossag]

Currently, the entire battery bank is just double isolated and floating, since none of the grid grounding circuits can handle the 500 or so A that the main 48 V bus can push, and I don't fancy upgrading them to handle that, hehe.

[@SuperBrainAK]

@@FFcossag yea that certainly makes sense, I would at the very least setup some kind of low voltage surge suppression to tie the system to ground incase it ever became in contact with a live conductor, since there is so many exposed terminals I can just see that being a major hazard. so put something in that at will short either the + or - to ground if the voltage goes over 70v of potential. Or at the very least some type of obnoxious alarm that will warn you if something like that happens.

[@FFcossag]

That wouldn't work, since it has no potential to ground - it's double isolated. If isolation fails in some device, trying to shunt it would be foolish since it's impossible to predict the amount of current available. I might mount a neon or LED or something between B+ and ground to show excess leakage, though - that's not a bad idea!

[@SuperBrainAK]

@@FFcossag yea there needs to be some kind of warning system. so you will be alerter before you go to mindlessly touch the battery contacts.

[@OffGridAussiePrepper]

Well I am confused after this vid, U now have a battery charger installed to charge up the 4 banks using grid power which is too expensive. Have u got an off peak rate? that ur gonna run the battery charger during off peak time? That cable thats heating up for the 300amp hour bank, cudnt u just run 4 lengths of it temporary until u get some decent cable? and ur miliivolt readings were in specified limits even thou they were higher then what the calculator said?

[@johncoops6897]

Yes - he charges at night at an off-peak rate. It was covered in a video a few weeks ago.

[@FFcossag]

This thing is mostly installed for a few reasons: 1) It's cool 2) It's free 3) Redundancy in case the MPI fails 4) Ability to charge from single phase sources 5) Convenient 48V bus extension for more batteries 6) Charging closer to the 100 Ah/300 Ah batteries, to make sure they get fully charged I do have variable rates for electricity, so if it's really cheap one night, it makes sense for me to just ultra-charge in a couple of hours for the upcoming day. The cable for the 300 Ah bank is going to be swapped out real soon. In actual use it doesn't get overloaded, since about 70 % of the current is drawn from the big banks. I'm just not prioritising it because it isn't that important - I could put it on a 32 A breaker for extra safety in the mean time. I'm fine with the voltage drop readings because I'm also measuring the voltage drop across the cable shoes and their connectors, so there is a little extra drop to be expected there. If I were to probe the cable by sticking needles through the insulation, it would be damn close to what the calculations show. I'm also not 100% on the exact length of the cable, it's 6 metres +/- 50 cm or so, probably a bit on the longer side of that.

[@OffGridAussiePrepper]

@@FFcossag thanks for the reply, i find it strange thou u get variable grid rates, it sounds like happy hour at the pub.

[@FFcossag]

There are two power companies available here, one offers a set price, the other offers variable. I went with the variable company since they pay market price for exported power from the solar system, whereas the set-price company pays about 1/10 market price for it. I also like the excitement of getting to optimise my power usage - I drive my EV VERY cheaply by charging at night!

[@OffGridAussiePrepper]

@@FFcossag right on brother.

[@--Zook--]

my daughter was born in 1997. She's 25 in case you didn't do the math.....lol