New system install OutBack GS8048 final items before startup

HarryN

I work with 48 VDC LiFe systems pretty often - not an expert but some experience with 48 VDC.

As far as tools and being near 48 VDC, what I do is wrap my tools with electrical tape, exposing only the one tip or socket that is needed to do the one application.  I have some wrenches with two box ends, but I only use one end, the other is covered.  This reduces the chance of a problem "when" I drop the tool. - Yes it happens.

I also wear thin rubber / latex gloves and safety glasses.  Even when you are very careful, an arc is always possible.

There are some rubber mats that you can buy - they are about 2x2 ft.  The ones I have have hex shaped holes in them for drainage.  I try to always stand or kneel on these mats when working to reduce the risk of being grounded.

This type of work is usually intended to be done by one person while another person is nearby "just in case".  Perhaps you have a friend who is an electrician or electrical engineer willing to come over and be your just in case person.

If there does happen to be a fire at some point, one of the best low cost methods of putting it out is a large amount of baking soda - dry.  You can buy a 50 lb bag and keep some of it in a bucket to throw on.  The nice thing about baking soda is that it is easy to clean up and non toxic.  There are higher performance dry agents, but they are harder to clean up.

HarryN

The biggest risk that I perceive during a system startup is all of that power coming down from the panels and "something" being wrong.  The easiest way to reduce this risk is:
- Do the startup during low light conditions - maybe even at night.  This way the risk of a connection having high current and voltage is reduced considerably.
- Let the breakers do the work of switching things on.  Those DC breakers are pretty impressive arc stoppers - let them do the more hazardous "last connection".  Worst case, if one does happen to blow - which is pretty unlikely, they are $20 - big deal.  If you buy a spare, probably you will own it a long time.

- Bring the system PV strings up one at a time, even consider to let each string come up and run for 1-2 days to make sure it is all working.  There is no downside to starting up slowly, especially if you are living there.
- Consider to purchase a DC clamp meter or two.  Last year I picked up a Extech AC/DC meter model 380950 for lower power (4-80 amp) use to supplement a 400 amp one.  I use the smaller clamp meter more than the bigger one, as it goes down to lower ranges, the larger one cannot measure.  I think I bought it through digikey or mouser.

Shunts and charge monitoring are interesting, but don't mean anything during startup.

HarryN

As far as getting power over to the battery for the genset starter, what I would be tempted to do is buy a 48:12 DC:DC converter.  This will let you maintain that 12 volt battery right off the 48 volt bank and skip all of that other BS. 

48-12 volt converts are widely used in golf carts, because many are 48 VDC battery packs, and still need 12 volt for lights, etc.  There are a number of brands out there, prices range from $25 - $500, depending on if you are happy with something that produces 10 amps at room temperature or 80 amps under industrial temperature range conditions. 

Since all of my battery banks are 48 VDC LiFe, AC loads are fed from the inverter(s) and 12 VDC loads are fed from these 48-12 converters.  I tend to use the $100 ones just for reliability and 300 watts is nearly always sufficient for a local 12 volt load.  That way I don't have to run 12 VDC over to a load - just 48 volt or AC.

In a perfect world, you would want this to be a true "charger" since it is powering that starter battery, but at least this will let you get moving.  There are battery tenders which are using to make a pulse out of this continuous power - sell for around $100 at auto parts stores or on line.

Long term, it might be worth replacing this battery with a 12 volt ultra cap, like a Maxwell engine start module.  Probably it is worth waiting for the existing starter battery to die, but they are impressive.  The most common use is on semi trucks / 24 volt applications.

HarryN

I am not completely sure about the relay for the exhaust fan on/off aspect.  Obviously the fan is needed when the batteries are charging, not completely sure about when they are discharging, but definitely there are still fumes in that area after charging has stopped.

If you are willing to get things started up and going under slightly sub - optimal conditions, then one option is to just run the exhaust fan 100% of the time for now and figure out the optimum on/off cycle over the next 12 months. 

In summer conditions and long solar charge times, the exhaust fan will need to run at least 12 hours anyway.    I think that fan uses less than 250 watts - it isn't nothing, but not the end of the world either.

HarryN

As far as the generator, you can get started with the system, at least the PV and battery aspect, with it disconnected.  Some people don't have all that much faith in generator frequency stability and will feed the generator output into the 48 volt DC system to just keep things going that way.  It isn't as efficient, but it is simple.  I don't know how to advise you on MATE setup details.

mike95490

HarryN said:

............
In summer conditions and long solar charge times, the exhaust fan will need to run at least 12 hours anyway.    I think that fan uses less than 250 watts - it isn't nothing, but not the end of the world either.

Gee, that's only 3KWh for the fan.   That much power would easily run a fridge for a day, maybe 2 if it was efficient.
I would argue that fan is way, way too large.
And in summer, assume charge starts by 9am, and in bulk for 3 hours, then absorb for 2 more, and 1 in float,  In real life, the first half of bulk, the batteries are efficiently charging and not gassing. So gassing starts 10:30am  and goes for another 4.5 hours, and maybe vent residual fumes for an hour after .  But not 12 hours, maybe just 6.

mike95490

Vic said:

In addition to the above good points,

Before connecting either cable from battery to the Radian DC box (the one with the DC Main inverter breaker),  carefully disconnect one of the battery-to-battery interconnecting cables.   This will allow connecting the cables from the battery to the main breaker,  and the battery DC -- buss without the risk of an incident.  With the main DC breaker/s OFF,  reconnect the previously disconnected battery interconnect cable,  being very careful (as you have already been when connecting all of the batteries together.......

I have a marine battery switch wired into the middle of my bank, right near the door, and can kill the battery power right there.
 There's been problems with some brands heating up and melting apart under steady loads, so research this a bit,

Estragon

Looks like the OP was a little over a year ago, so hopefully he has the fan etc. figured out by now.

His batteries were AGM so wouldn't needed much ventilation.

Alan

Yep, it's been just over a year and it's been running fine. The fan, common bath fan 120v, it's hooked to a relay to the 12v output on the radian. It comes on and off when the radian tells it to.

Works fine. The system is working fine too, generally. When late fall his the sun was so low I had to supplement the battery charging with the mini grid set up. Still don't have it set up to get electrical company pay back.

Likely will do that this summer.

Estragon

Good to hear everything worked out. If power consumption was an issue you could probably run a small vent fan directly off the 12v relay on the radian - something like the Zephyr vent sold by our hosts which takes ~3 watts. If it ain't broke though...

HarryN

Sorry for adding comments then to this 1 year old thread.  I saw January and didn't look at the year.