Solar Vd

Submitted: Saturday, Mar 21, 2020 at 19:38
ThreadID: 139821 Views:726 Replies:3 FollowUps:8
Howdy

As per my previous post, I am looking at setting up solar for camping. We run a very power hungry camp. Being in the Top End, fridges and fan have long run times.
I have ordered a 200w flexible panel from Sunyee. This panel can't be put in series or parallel according to the supplier.
Plan is to run several panels, or at least carry several panels. How many I set up at any one time will depend on duration of stay in 1 place and load.
Obviously there are some efficiency gains running 24v, not to mention the cable sizing.
That said, should I stick with 12v, Vd may be an issue.
Now if I was running from a battery to a load and had a .5 Vd @ 12V this would be a major issue. But what about on the supply side of the MPPT. Just how real would the effect be?
Also, what formula are people using here to calculate Vd. I have a copy of a cable sizing sheet from Ashdown Ingram's, This gives a recommended length/size chart but no actual properties of each cable that I can punch into a formula. I will be using 1 size cable from panels to large Anderson plug on car, then bigger cable from there to MPPT. Though I will have to crimp it down in size before termination into the MPPT as the maximum cable size will be 6 B&S and I will probably be running 2 B&S. With 6 B&S being used out in the "field".
Looking at the 50A version
Panel sizing around 600w and maybe a little more.
Battery capacity with boat included 700 a/h
I was also thinking of going from MPPT to chassis and from Anderson plug to chassis for the negative and just running the active.....

Thoughts folks?
(let me guess, run them in series :-) or possibly series/parallel

Cheers
Lyndon
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For the clock may then be still

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Reply By: RMD - Saturday, Mar 21, 2020 at 20:45

Saturday, Mar 21, 2020 at 20:45
Lyndon.
Are you sure the Chinglish of the Sunyee site means no series or parallel. Cannot see why not, apart from very low revers diode voltage in any diodes. Even that shouldn’t be a problem with the input into MPPT unit. Running two or even three panels in series ( if MPPT charger can handle the Max developed input voltage) will vastly lessen the requirement of heavy cables to reg but still deliver the sun energy to the reg for appropriate processing. Any voltage drop effect in the cable will become much less percentage of loss than other options.
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Follow Up By: Member - lyndon NT - Saturday, Mar 21, 2020 at 22:17

Saturday, Mar 21, 2020 at 22:17
Indeed the Vd would be lower and the cables would not have to be so MASSIVE. I will ask them why you can't put them in series.
Cheers
Lyndon
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Follow Up By: RMD - Saturday, Mar 21, 2020 at 23:07

Saturday, Mar 21, 2020 at 23:07
Lyndon.
Something you have mentioned again is use of fridges and fans. I asked if you have decent insulation around the fridges and yes, most have fans in them. If relying on just a fridge insulation and the proprietary std insul cover, that maybe half the problem with the power hungry aspect. No good having fridges running all the time or near to. In the tropics you need far more insulation, it is relatively cheap to add and reduces your solar panel size and wattage requirements along with minimizing reg size and battery bank AH size too.
Edit
With wire size, double the voltage and same wire size carries twice the energy to the reg. Many people have flex panels in series on van roof. Why not Sunyee panels. They simply buy and resell panels, they aren't actually Sunyee made. Just didn't make sense.
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Follow Up By: RMD - Monday, Mar 23, 2020 at 11:33

Monday, Mar 23, 2020 at 11:33
Lyndon.
If using. Victron 100/50 , you can SERIES three panels, possibly four panels of same current ability and have nearly 100v DC going to the Victron and allowing it to make the 12v charge current from that. It will have a wattage rating so you can't go pass that wattage input amount. ie, maximum total voltage and amps multiplied together to get available watts. I would also have any boat battery with it's own panel and reg so it is able to be fully charged when required. ie, early morning the boat battery IF attached to main system would be at main system state of charge after the night running of the fans lights and fridges.
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Follow Up By: qldcamper - Wednesday, Mar 25, 2020 at 13:30

Wednesday, Mar 25, 2020 at 13:30
if you are thinking of running voltages any higher than 36 volts I would recommend getting a household sparky to install it. There are some serious shock risks with voltages above that which are considered potentially fatal, DC is more dangerous than AC when in higher voltages.

I am not sure if a license is required for under 100 volts DC but it is bloody dangerous and should be treated with the same safety respect as 240 volts.

We were warned in TAFE that even 48 volt electric fork lifts can deliver fatal shocks.


























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Follow Up By: Member - lyndon NT - Saturday, Mar 28, 2020 at 09:18

Saturday, Mar 28, 2020 at 09:18
Hi qldcamper

Thanks for your input. Just about any voltage ac or dc can be dangerous under the right or wrong conditions, depending on how you look at it.
However it is generally recognised that a touch voltage below 50v ac or 120v ripple free dc is safe.
These this vary greatly depending on the impedance of the person at the time of contact with a live part.
So I can't see myself going outside these parameters with 3 or 4 panels.
Rooftop solar if utilising a string set up, yes, dangerous. Hence why some are now going to Micro Inverters, along with other reasons.

Cheers

Lyndon
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Follow Up By: Allan B (Sunshine Coast) - Saturday, Mar 28, 2020 at 10:42

Saturday, Mar 28, 2020 at 10:42
.
The subject of electric shock on the human body is complex and interesting.

The current Australian Standard definition for Extra-low Voltage (ELV) is 'less than' 50v for ac and 120v for ripple-free dc as Lyndon has said. In earlier Standards it was 32vac and 115vdc. It is deemed that contact with ELV is unlikely to be unsafe. However, there are many variables involved and there have been cases of fatality at voltages lower than specified in the current Standard.

It is not true that dc is "more dangerous" than ac. The Standard specifications above reflect the greater danger of ac voltages.

The real danger lies with both the nature (ac or dc) and the current that is imposed on the heart and the duration of the application. This current, with a maximum safe level of typically 30mA ac (300mA dc) and 0.5 seconds, is the cause of heart fibrillation and fatality. And the current itself is dependant on not only the applied voltage but also the electrical impedance of the body which varies according to factors such as the skin resistance (dry or wet) and the area of electrode contact.

Although I have received many electric shocks in my time, and clearly survived, it is generally best if all are avoided. Residual Current Devices (RCD's) have been instrumental in reducing serious electric shock for users of appliances but those working directly on electrical installations are at greater risk.
I would not consider that the 12v supply in automobiles presents any shock risk but there is still some risk from burns and eye injury from severe short circuit events.

On the subject of licensing, an Electrical Worker's licence (different title in different States) is required for work above the level of Extra Low Voltage however it is still required that those working on ELV are "competent" although the definition of 'competent' can be difficult to determine.

Note also that, contrary to general belief, the Australian Standards are not a lawful prescription. They are a 'recognised' standard only. Their legal application is embodied in the legislation of the individual States and these are not consistent, so it is necessary to be familiar and work within the Regulations of each State.
Cheers
Allan

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Reply By: Allan B (Sunshine Coast) - Saturday, Mar 21, 2020 at 22:44

Saturday, Mar 21, 2020 at 22:44
.
Hi Lyndon,

This chart may provide what you are looking for. Note that for practical purposes, B&S and AWG numbers are the same gauges and the chart also provides a metric (mm2) column.

A drop of 0.5VD of 12V represents a loss of about 4% of your energy whether it be in the charging input to your battery or in the supply from the battery to a load. It is not a great loss in either but only you can evaluate its significance to yourself in selecting cable size based on cost and convenience.
Cheers
Allan

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Follow Up By: Frank P (NSW) - Sunday, Mar 22, 2020 at 09:09

Sunday, Mar 22, 2020 at 09:09
"Indeed the Vd would be lower and the cables would not have to be so MASSIVE. I will ask them why you can't put them in series."

Of equal research value, why can't they be wired in parallel (per your openjng post)?
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Reply By: Member - Bigfish - Sunday, Mar 22, 2020 at 11:20

Sunday, Mar 22, 2020 at 11:20
I,ve got several sunyee panels. Had them for a couple of years. I use them in parallel all the time...3 x 100 watts. As yours will be the same size, output and manufacturer I cant see the problem..
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Follow Up By: Member - lyndon NT - Saturday, Mar 28, 2020 at 09:01

Saturday, Mar 28, 2020 at 09:01
Hi Bigfish

Thanks for your reply. Here is what Sunyee had to say when I asked why they state not to run panels in Parallel or series.

"Hi Lyndon,

It's due to the diodes inside the flexible solar panel which are fragile and will be gradually damaged in a parallel or series connection.

Regards,

Bob"

Which is really disappointing. Obviously they have tried to save a couple of dollars on the components.
However it does state this on the website, so I can't really complain.

My panel turned up this week, so may get to some testing this weekend. At 200w (allegedly) it is a bit large, 100-150 would be more manageable.

Now running in parallel will save a bit of cable but it isn't going to help me solve my Vd problem.

Cheers

Lyndon
Now is the only time you own
Decide now what you will,
Place faith not in tomorrow
For the clock may then be still

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