confirm my el. current calcs please!

[vas]

sitting at home thinking...

I have 2X300W solar panels connected to a Victron BlueSolar MPPT 100/30 (as in 100V max in, 30A maximum)
this connects to the service bank which is 4X6V Trojan T105RE batteries
To finish off the setup, there's also a Mase 8KW generator.

About to order a inverter or mostlikely a charger inverter to replace the Victron Phoenix 24/60 currently onboard and the broken modified sine inverter I have.
My options are Victron Multiplus 24V 2000W (or VA whatever), or a 24V 3000W (again or VA)

Typically on my mobo, the 230V battery charger is not used since I added the solar and never use shore power as the pilar is too far and tbh there's no need for it.
Consumption is mainly two fridges and led lights/phones/notebook charging except when I'm working on board where I get to use various tools.

I do run the generator on the odd occasion I'm in a port and its too amazingly hot to cool the cabins for half an hour or so - has happened once or max twice a year thusfar)
Main use of the generator is to run the watermaker which is a good 10-11A @ 230V

So, was thinking is it reasonable to expect that the system will cope running some lunchtime the watermaker from the inverter???

Calcs say:

230V * 11A = 2500VA

The BlueSolar mid day in the Med will provide 18-19A

Trojans state that they can accept 115mins discharge @75A

so if say I run it off the 3000W Victron inverter (mind there's an Invertek driver 3ph inverter driving a 3ph motor so soft starting and no peak from the motor) can I assume that the setup will run for an hour (don't want it more than that every couple of days )

2500VA needed is 100A @25V (is that where I do the calcs or at 24V??)
Is it safe to assume 20 of that A from the MPPT and the other 80A from the Trojans for an hour?

am I about right or way off (shouldn't be!) ?

Need to decide if I have chances of running it like that or don't bother and get the smaller inverter. I could get a 5KV inverter as well s/h

cheers

V.

 

[LadyInBed]

2500VA needed is 100A @25V (is that where I do the calcs or at 24V??)

I would have thought that it's one of the same thing, your 4 batteries should be up or over the 26v mark. I would use the 25v figure.

 

[PaulRainbow]

Ball park figures ;

Your water maker is drawing 2500W so a 2000W inverter won't run it.

The 3000W inverter will draw 125A with a 2500W load.

That's 125AH, less your solar yield, say 15ah, based on your 18-19a figure, less a little for other equipment consumption. that's 110ah.

If your Trojans are brand new, tip-top and fully charged, that'll take them down to 50%.

 

[vas]

Ball park figures ;

Your water maker is drawing 2500W so a 2000W inverter won't run it.

The 3000W inverter will draw 125A with a 2500W load.

That's 125AH, less your solar yield, say 15ah, based on your 18-19a figure, less a little for other equipment consumption. that's 110ah.

If your Trojans are brand new, tip-top and fully charged, that'll take them down to 50%.

thanks for the replies gents,


Paul, out of curiosity, is the 125A you quote due to the efficiency of the inverter? I'd have hoped it's better than that tbh!

Trojans are 2yo as the panels, plan is/was to run that setup for a hour max midday with the batteries already full and at max sunshine (July August - OK theoretically not sure what we'll do this year...).
Main idea is that I do have all that solar doing bugger all from midday (just topping up the Trojans from the 4A the two fridges occasionally take out) I might as well get them to do something serious

cheers

V.

 

[pvb]

Ball park figures ;

Your water maker is drawing 2500W so a 2000W inverter won't run it.

The 3000W inverter will draw 125A with a 2500W load.

That's 125AH, less your solar yield, say 15ah, based on your 18-19a figure, less a little for other equipment consumption. that's 110ah.

If your Trojans are brand new, tip-top and fully charged, that'll take them down to 50%.

I reckon you need to take into account the Peukert effect; at such a high discharge rate the capacity of the batteries will be much less. I don't think they'd last an hour with that load.

 

[superheat6k]

I would suggest the power efficiency both into and out of the batteries and the losses in the inverter will likely exceed 25% if not considerably more. So when sizing like this you need a good deal of extra capacity in both the Inverter and Batteries. I would suggest the 3,000 VA is going to be borderline and 2,000 VA way too small. I would also go really heavy on the cabling, with at least 50% oversize - 125amps through the cables for an hour is a continuous hefty load, so keeping the volts drop minimal will be essential. You might wish to up your battery bank too.

 

[PaulRainbow]

Paul, out of curiosity, is the 125A you quote due to the efficiency of the inverter? I'd have hoped it's better than that tbh!

Rule of thumb for 12v inverters is to divide the watts by 10, to get amps. Would be half that for 24v.

This is pretty much what i've seen in the real World too. In fact, i fitted a Victron 3000w 12v inverter last Summer, on a boat with an all electric galley and did some testing with the owner and it was pretty much bang on divide by 10.

I think running a 2500w load for an hour would be bad news for your batteries. At the very best you'd be cycling them to 50% daily.

 

[PaulRainbow]

I reckon you need to take into account the Peukert effect; at such a high discharge rate the capacity of the batteries will be much less. I don't think they'd last an hour with that load.

Good point Pete. So many variables to take into account with such high rates of discharge (temp etc, especially in the Med), it'd be hard to pinpoint it. I can't recall subjecting that size battery bank to such a high load for such a time to draw on any real World experience, but i'd hazard a guess that it could pull the batteries down to about 80%, if they are in good shape.

 

[vas]

thank you guys

remember it's a mental exercise to decide how much I'll spent on the charger/inverter combo.
No plan to up the battery bank at all.
No plan to do that everyday, maybe 3times a week for 3-4weeks each year, as there's always a day I move from one anchorage to another in the early afternoon and with the two engines running I can also run the generator without much fuss/extra noise and fill up the tanks.
regarding load size and batteries accepting it or surviving, the Trojan spec sheet (if it is to be believed) says they will: https://www.trojanbattery.com/pdf/datasheets/T105RE_TrojanRE_Data_Sheets.pdf

Note Capacity Minutes:
@25A is 447 (7h45min)
@75A is 115 (1h55min)
extrapolating that I expect @100A it's going to be more than an hour

Cycle life graph at the bottom of the datasheet says that at 50% discharge they'll manage more than 1500cycles (=days in my case) I can definitely live with that tbh.

Mind I can alter pressure/rpm of the 3ph motor running the watermaker and gain an amp or so
Victron will be next to the batteries 1m cable to V+, 1.5m cable to V-

Needless to say IF I do that, first few times I'll be there with my IR thermometer to check the process and temps full time!

Probably first thing to do is establish current draw of the whole setup @230V accurately (I'm stating what the needle in the el.panel reports - I'll test with my amp clamp)

cheers

V.

 

[Pete7]

Vas, just as a side issue, you may find that a 300w panel through a Victron MPPT could output 20A plus, or at least I hope so because I have just fitted one. If you have two 300w panels but only the 100/30 MPPT you may be short changing yourself in ideal full sun conditions. Won't make any difference when it's raining.

There is a calculator on the Victron site to work it out if you need it. If you do change the MPPT, the smart Solar range incorporates bluetooth but the Blue Solar doesn't if that helps.

Pete

 

[PaulRainbow]

Vas, just as a side issue, you may find that a 300w panel through a Victron MPPT could output 20A plus, or at least I hope so because I have just fitted one. If you have two 300w panels but only the 100/30 MPPT you may be short changing yourself in ideal full sun conditions. Won't make any difference when it's raining.

There is a calculator on the Victron site to work it out if you need it. If you do change the MPPT, the smart Solar range incorporates bluetooth but the Blue Solar doesn't if that helps.

Pete

Fair point Pete, but i hope/expect that Vas has the panels wired in series, he does say he gets 18a-19a, which would be about right for a series installation.

 

[pvb]

Vas, just as a side issue, you may find that a 300w panel through a Victron MPPT could output 20A plus, or at least I hope so because I have just fitted one. If you have two 300w panels but only the 100/30 MPPT you may be short changing yourself in ideal full sun conditions.

Note that Vas is running a 24v system.

 

[vas]

Pete, running 24V as pvb mentions, they are in series as Paul notes, and yes before buying I spent a couple of evenings with this excellent Victron XLS file.
I was mainly worried of exceeding the 100V limit, but I've not seen it go over 91-92V so I'm fine. This way I can run thinner cables (still a size up from recommended because I could) and not have any voltage drop issues.
Indeed my 600W wont produce more than 21A max at 20C (which is a joke in the scorching sun midday, hence my calcs on 18-19A). Problem is that cannot really see such uplifting numbers as by 11am batteries are rather full and on folat only take a few amps that's one of the reasons of thinking of doing this with the watermaker.
If I feel like going out tomorrow, I'll run the geny and measure current draw on the 3ph motor inverter input and report. Will also play a bit with waterpressure and note the effect it has on current draw although I cannot go down more than 40-50psi as output will drop and membrane fouling will rise.

cheers

V.

 

[PaulRainbow]

Rather than running the watermaker for a hour, three times a week, could you not run it for a shorter time on more days ?

 

[vas]

Rather than running the watermaker for a hour, three times a week, could you not run it for a shorter time on more days ?

Paul, of course, the 1h is ideal and also depends on ppl onboard, if it's just the two of us, wont bother tbh and only run it when changing anchorage the 450lt will last for a few days anyway.
if we are on a nice isolated spot and 6 onboard, I'll probably run it as long as the batteries can handle it each noon...
it's a suck it and see case by the looks of it as it will be fun making water silently on the cheap but don't want to have to fork out for a new set of Trojans soon

V.

 

[PaulRainbow]

Paul, of course, the 1h is ideal and also depends on ppl onboard, if it's just the two of us, wont bother tbh and only run it when changing anchorage the 450lt will last for a few days anyway.
if we are on a nice isolated spot and 6 onboard, I'll probably run it as long as the batteries can handle it each noon...
it's a suck it and see case by the looks of it as it will be fun making water silently on the cheap but don't want to have to fork out for a new set of Trojans soon

V.

My feeling is, an hour wouldn't be good for the batteries, but 20-30 mins would likely be OK. In your shoes, i'd be inclined to go for the 3000w inverter anyway.

 

[vas]

sure 3 or even 5k (s/h)
If I opt for the 2K, means I'm not going to be trying this at all!

Depends on what I come across and how much I'm going to recoup selling my Victron 24/60A charger which is sitting there doing nothing for the last three years...

cheers

V.

 

[vas]

turns out that I won on ebay a s/h 24/3000/70 Victron multiplus.
So next week I'll be able to report on how it fares on the above.
Worse case scenario, I'll be baking a loaf of bread each morning, making lots of espressos on my La Pavoni and heat water (as per Vic's q in another thread) with the excess amps

V.

 

[PaulRainbow]

turns out that I won on ebay a s/h 24/3000/70 Victron multiplus.
So next week I'll be able to report on how it fares on the above.
Worse case scenario, I'll be baking a loaf of bread each morning, making lots of espressos on my La Pavoni and heat water (as per Vic's q in another thread) with the excess amps

V.

Look forward to reading how it all goes.

 

[vas]

Look forward to reading how it all goes.

just a small update since the 3kVA inverter should arrive early next week,
so today had a go with my ampclamp thing and measured the phase on 230V in from the generator.
it was consistently 9.7A at full chat (800psi).
TBH no point running the watermaker at lower output/pressure (with the danger of fouling the membrane) as it would only save .2A and if that.

so 9.7A @ 230V is the load.
by midweek I'll report if it works (hopefully will be sunny as well as weather is crap over the last week or so...)

cheers

V.