Author Topic: System Voltage  (Read 616 times)

Bob D

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System Voltage
« on: October 24, 2016, 08:03:21 PM »
I am relocating my panels (Vmp=29, Imp=7.4) to be very close to the 24V battery.
Currently they are a fair distance away and so I decided to use 4 strings of 3; Vmp = 87V.
From an charging efficiency standpoint, would I be better off to configure as 6 strings of 2; Vmp=58?
If so, what approximate affect will this have on charge controller efficiency?

Second question: Does anyone have experience using a soft starter to reduce the inrush current on a 120V capacitor start motor? Schneider makes what appears to be a suitable device. My goal is to reduce the shock on the inverter, having to go from idle to a slight overcurrent when the pump motor starts.

Thanks
Bob

12-215 watt panels, Midnite 150, 790 A 24V industrial battery, Magnum 4024 inverter

Classic 150, Magnum 4024, 12-215W panels, 12-85-13 forktruck battery

russ_drinkwater

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Re: System Voltage
« Reply #1 on: October 25, 2016, 04:45:34 PM »
My system is 24 volt and I run the solar arrays at 58 volts with no problems.
Regs still switch on cooling fans fairly regular at 30 amps each in fair sun.
Standalone. 20 Hyundai x 220 watts panels, 2 x classic 150's, Latronics 24 volt 3kw inverter, 8 x L16 Trojan 435 amp hour Batteries and Whiz bang Jnr, 12 Rolls surrete  4KS 25P  batteries and WBJ.
Grid tie feed-in, 12.5 kw in 3 arrays generating 50 kws per day average. Solar river grid tie inverters

Vic

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Re: System Voltage
« Reply #2 on: October 25, 2016, 05:31:45 PM »
I am relocating my panels (Vmp=29, Imp=7.4) to be very close to the 24V battery.
Currently they are a fair distance away and so I decided to use 4 strings of 3; Vmp = 87V.
From an charging efficiency standpoint, would I be better off to configure as 6 strings of 2; Vmp=58?
If so, what approximate affect will this have on charge controller efficiency?
   ...

Thanks
Bob

12-215 watt panels, Midnite 150, 790 A 24V industrial battery, Magnum 4024 inverter

Hi Bob,

With strings of two PVs with a Vmp of about 29 V,  there is plenty of headroom for the Classic 150.   And the Classic should run a bit cooler with that lower string Vmp.

One might guess that the Classic might be about 3/4 to 1 percentage point improved efficiency ...  not huge,  but still a bit more power output (with short runs from the PVs to the CC),  and a Classic that runs a bit cooler.

Opinions,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

CDN-VT

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Re: System Voltage
« Reply #3 on: October 26, 2016, 01:06:42 AM »
Im in agreement with Vic .
Also you  will have  6 times 7.4 amps with 6 0f 2 over only 4 time 7.4 Amps .. @ 58 Vdc , so your highest eq Vdc is 29 Max  so you can still make that  EZ & MPPT with a 58Vdc input.
 

What size is this motor that a 4000w inverter is having a problem with ?
If it is a deep well submersible I have removed the foot valve in the pump & installed in one way checks in the just before & after the pitless adapter .

That way the pump has no load on the starting , there still a surge , just not full load to overcome , since the pressure is held back and the pump spins up with less load ..
Just a trick I have used .  & I use two units to make them serviceable if need be .


VT
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c -30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 2sx3 parallel for 24 V Classic 150 -440 Ah  SS300 for lights & overhead door. Building the 33 panel 48 volt system now

Powerplay

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Re: System Voltage
« Reply #4 on: October 26, 2016, 06:48:43 PM »
Quote
Second question: Does anyone have experience using a soft starter to reduce the inrush current on a 120V capacitor start motor? Schneider makes what appears to be a suitable device. My goal is to reduce the shock on the inverter, having to go from idle to a slight overcurrent when the pump motor starts.

Interesting point.  The 4024 can surge to about 5800W for 5 seconds and that would require 0000 cable & 250A breaker.  But that sounds like quite a surge.

As to your VmP at 58V that is almost perfect for a 24V battery IMO.  One of my controllers was charging my 24V battery bank all summer at VmP = 56.7.  My other controller has been at VmP = 75.6 and it runs a bit hot, IMO, but still does fine.  The Classic is an impressive regulator, IMO.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

Bob D

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Re: System Voltage
« Reply #5 on: October 27, 2016, 01:47:03 PM »
Thanks to all for the replies.
I knew the 58V strings would work fine, but I was wondering if there was any quantitative inof about the efficiency difference.
Sounds like it is a marginal improvement.

regarding the motor starting, I should have posted it separately, I guess.
In any case, the specifics are that I have two 1/2 HP motors in my water system, each with a running current of about 4A, or about 500 watts each. However, the inrush current when starting is about 5 times the full load rating, or about 25A each (about 3000 watts).
It is possible that the two motors start simultaneously, although that is infrequent.
When the motors start, there is a momentary flicker of the lights, although it is a small enough voltage drop that things like computers are fine.
My inverter is fed with 4/0 copper cables, and has a 250A breaker.
I see 250A occasionally during the motor start cycle.

It all works fine but I don't like the flicker, and I wonder if the inverter frequently going from a fairly low background load to a overcapacity surge will have any detrimental effect on the inverter longevity. The inverter typically runs with the cooling fans either off or on low speed, and they immediately ramp up when the pumps are starting.

Soft start devices, which aren't terribly expensive, would limit the starting current, and wouldn't affect the water system performance because it doesn't matter whether the pumps come up to speed in a fraction of a second or over, say, two seconds. There is limited information about the effect of reduced voltage starting on capacitor start motors - or at least there is little experience based info, just a lot of speculation. Thought I'd see if anyone here has any such experience.

Sorry for the long post.
Bob

Classic 150, Magnum 4024, 12-215W panels, 12-85-13 forktruck battery

Powerplay

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Re: System Voltage
« Reply #6 on: October 27, 2016, 05:42:35 PM »
Quote
or about 25A each (about 3000 watts).

Does that ever peak at the same time (6000W)?  Top surge rating is 5800.

Quote
I see 250A occasionally during the motor start cycle.

Does the breaker ever trip?

Quote
The inverter typically runs with the cooling fans either off or on low speed, and they immediately ramp up when the pumps are starting.

I don't think the fan logic on these inverters is very sophisticated (not heat dependent but rather current dependent).  This is from observation on a extra hot day the fans are still loafing along until some more load is applied even though the chassis is already hot to touch.

Quote
There is limited information about the effect of reduced voltage starting on capacitor start motors -

Agree.  Mostly what one reads is all about ambient temperature de-rating.  There is very little about voltage de-rating.  Maybe ask Magna-sine about it.  I'd be interested in what they say also but none of my loads including saws and vacuums surge close to that.  I'd still be interested to know what has detrimental effects on the lifespan of these devices.
41 degrees N, 255 Ah 48V AGM, MagnaSine 4448 Inv, 3500W PV, Midnite Classic 150 A (12/6/15), Midnite Classic 150 B (4/14/16), WBjr, BTS, MNPV6 X 2, SPD X 2, Apps: Mini Split AC, Car Charger, Water pumps, Lighting, -> 48V string plan 500W, 94.5VmP, 112.5VoC, -15C - 40C TCVoC -.3%, TCIsC +.04%

Vic

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Re: System Voltage
« Reply #7 on: October 27, 2016, 08:32:20 PM »
Hi Bob,

A couple of general comments;

A 250 A DC surge is really huge,  as you know.

A Forklift battery generally has fewer plates,  so it would be expected to have a larger voltage sag for large surges,  than batteries that are designed more for off-grid use.

It has been said,  that Magnum inverters have considerable AC voltage sag with high peak currents.   And,  of course,  a 24 V system,  essentially doubles the DC current,  verses 48 V systems,  all else being equal,  and thus would generally show more flicker.

And,  fluorescent lights,  generally suffer from more dimming than do other types of light,   although,  generally,  CFLs are fairly immune to flicker.   Some LED lights  flicker a bit,  and others very little at all.

Just my opinions,   FWIW,   Vic
« Last Edit: October 27, 2016, 08:33:54 PM by Vic »
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

CDN-VT

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Re: System Voltage
« Reply #8 on: October 27, 2016, 11:34:38 PM »
Im reading twice 1/2 hp units that can come on at the same time ?

You better start a new thread on this water question .
Canadian Solar 350W 37.6 VOC  30.6 VMP 8.22 ISC 7.87 IMP ,-15 c -30c max  4 strings in 2 in Series for 24v Classic 150 -1020 Ah  Freezers & fridges ~~~ Second Array same panels of 2sx3 parallel for 24 V Classic 150 -440 Ah  SS300 for lights & overhead door. Building the 33 panel 48 volt system now

Bob D

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Re: System Voltage
« Reply #9 on: October 28, 2016, 05:31:42 PM »
Yeah I'll start a new post - should have done two to start with.
I'll move the motor starting/inverter subject to the new one.

Still would be interested in any quantitative info re: charge controller efficiency versus system voltage.

Classic 150, Magnum 4024, 12-215W panels, 12-85-13 forktruck battery