Help With Using 36V? solar panel for 12V batteries

tuggersbmx · Senior Member

Help With Using 36V? solar panel for 12V batteries

T1 Terry · Guru

What brand, model number is the MPPT controller? The series string from the 2 panels would be 90vdc open circuit, so the controller would need to be able to handle 100vdc.
To get a rough idea of the charging voltage you can expect, 400w x 0.8 (80% out of the panels) = 320w. Divide this by 12v gives you 26.6 amps. You might see this or even a bit more in the middle of the day in the middle of summer, but in reality I'd expect maybe 20 amps in summer and maybe 10 amp in winter down south.
As far as changing the panels to 12v nom. panels, depends if the MPPT regulator can handle the input from the 2 panels in series and it actually puts out between the 10 amps and 20 amps, depending where you are at the moment. 10 amps in South Vic or SA, more towards 20 amps if you are in Nth Qld around this time of yr.

T1 Terry

tuggersbmx · Senior Member

Hi T1 Terry. The regulator is a Powertech mp-3735 It states the following. Max PV array. 360w -12v battery 720w -24v battery Max input current - 30adc Max input open circuit - 65vdc Max load current - 30a DC So would it be usable as a 12v regulator but I would not get the full amps of charge that the panels are capable of or would I damage the regulator? Or could I run the battles as a 24v bank and then use the regulator with the two panels and get full charge from the panels. Cheers. Mick

Jaahn · Guru

tuggersbmx wrote:
Hi T1 Terry. The regulator is a Powertech mp-3735 It states the following. Max PV array. 360w -12v battery 720w -24v battery Max input current - 30adc Max input open circuit - 65vdc Max load current - 30a DC So would it be usable as a 12v regulator but I would not get the full amps of charge that the panels are capable of or would I damage the regulator? Or could I run the battles as a 24v bank and then use the regulator with the two panels and get full charge from the panels. Cheers. Mick

Hi :)

My two cents worth. You are correct that a proper MPPT regulator should convert over voltage to extra current if the panel input is within the specs. That is the reason for using them and they do work OK if you have a good brand. However that unit of yours is not a good brand and a quick google shows unhappy customers !! I might say just looking at it it is not up to doing the job well. Sorry.

My suggestion is to keep the panels but get a better MPPT unit, say a Tracer which are the cheapest that work OK, or a better one like a Victron (or others too). Get one that is rated for 400W+ and put the two panels in parallel into it. You will have a satisfactory setup if you use generous sized cables and the regulator is close to the batteries.

Read the other threads here for background and there is a search function near the top in the blue band marked "search". Or ask more question after you read a bit more.

A question. The Nissan is probably a 24V vehicle system, it may suit to have a 24V house system too so you can charge from the alternator also. You might need to use a voltage "dropper" to use some 12V things but you can get 24V items to use too. You can still use the good MPPT reg to charge at 24V with those panels.

Jaahn

PS those panels are 'nominal 24V' panels. Nominal 12V panels have about half the voltages of those.

-- Edited by Jaahn on Tuesday 18th of June 2019 10:25:09 AM

denmonkey · Senior Member

Tug, that sounds about the same as my set up, with the epever tracer as recommended by Jaahn above.

I have 2 x 185w ~36v panels but set up in parallel, so maintaining that approx voltage into the controller.
I did choose one that could take an input up to 100v if I decided to go in series with the panels.
Its just nice to have the option.

My panels were only installed a little while ago and I'm yet to see a full summers day of sun to see what I can get out of them under perfect conditions but even in winter with minimal sun, they cover my needs.

I'm with Jaahn, turf the controller, keep the panels. That is, if you can test the panels and see what their output levels are . If it's inline with the sticker, I'd keep hold of them

I reckon there are bargains a plenty with the old house panels being sold on the second hand market these days.
Get a controller that can handle them and a set up can be had very very cheaply.

E.g if your panels are no good. replacement ones can be found on gumtree for probably around 50-70 bucks a piece if you keep your eye out.

cheers Brett

tuggersbmx · Senior Member

Hi Guys,

So I have wrapped my head further around this situation with your help (thanks a lot) and I agree that keepiong the panels I have and buying a nedw MPPT regulator tracer unit and then I should be fine.

Use those solar panels to the new tracer regulator to the 24V 300ah batter bank. I will use one fuse box stright form the 24V system to run my 24V items and then a dc to dc 24 to 12v reducer to a 12V fuse box to run my down lights and a few other 12V accwessories.

I will keep the older regulator ( Powertech mp-3735) to use on a seprate solar panel to provide a seperate set up to charge my 24V bus starting batteries.

I then have a 3000w generator to run my reverse cycle roof mount air con which has a battery to start it from a remote. I have a small 12v 24ah battery for that which I might buy a 50w solar panel and use my other 12V basic regulator to keep that battery charged.

I think I am on the right direction now.

Any further advice?

cheers

Mick

tuggersbmx · Senior Member

do you guys have a link to a suitable and reasonably priced tracer with 100v capacity?

cheers

Jaahn · Guru

tuggersbmx wrote:
do you guys have a link to a suitable and reasonably priced tracer with 100v capacity?

cheers

There are lots of them on ebay you will have to search. Here is the specs of the range. What you need is the 2210. There are several types now and I am not sure of the difference but the numbering system is the same, but I have the older simple models bought a few years ago now. I might suggest you get it with a separate remote meter also for a bit extra so you can see what is happening easily (but not essential). Find a seller who has that as a combination. The regulator should go close to the batteries so the remote meter can be put where you can see it. I usually buy from a seller in Australia rather than China for a bit extra.

I have my MH wired so the panels charge the vehicle batteries and then a VSR automatically switches the house batteries in after the voltage rises a bit, This works for both running the engine and for the solar charging. So the vehicle batteries are always fully charged first(helps their long life). Works well IMHO. I have a very big cable connecting the two systems with the VSR.(Voltage sensitive relay) The house batteries get charged when driving and in bad solar weather you can top them up by starting the motor for a bit.

Cheers jaahn

Here is one 24V VSR. Plenty of 12V units. These suit the old charging systems that do not have a 'silly' smart alternator !

https://www.ebay.com.au/itm/Enerdrive-12V-140A-24V-140A-Dual-VSR-Relay/282569423992?hash=item41ca733c78:g:f80AAOSwYS9ZZuZz

-- Edited by Jaahn on Wednesday 19th of June 2019 05:17:04 PM

tuggersbmx · Senior Member

Cheers for all the info guys. Il be buying a tracer mppt regulator tomorrow. I'm just trying to figure out the amps I need to cover for the system. So it would be best to run the panels joined as 400w? Would I need a 30amp tracer or lower? Cheers.

tuggersbmx · Senior Member

Also I'm a little confused as to what 24v to 12v step down converter to buy. I run that in-between the 24v house battery bank and a fuse box that will hook up all my 12v lights and a few other items. My question is if I buy a 30a step down converter to the fuse box and then have the different sized fuses in place to protect the lights ect, will those fuses just keep blowing because there's 30a running to the box? Or will it be fine? Hope that makes sense. Learning a bit more as I go at the moment. 24v system is new to me. Cheers

denmonkey · Senior Member

this is the one I went with for mine.

www.ebay.com.au/itm/EPEVER-10A-20A-30A-40A-MPPT-Solar-Charge-Controller-12V-24V-Auto-Negative-Ground/351657683105%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

I went with the 40A and the mt50 controller which is very handy.
You can alternatively get a wifi dongle that plugs in to the unit and you can monitor from your phone.

I went with 40 to give myself some head room and for $190 with the control panel, I figured why not.
It will also allow me to add portable panels into the system and still be under that 40A limit.

Can you explain what you mean by joined as 400w. If you have 400w, how you join them won't change that they are 400w worth of panels.

Re the step down side of things. The fuses on the 12v side of things will need to be sized to meet the requirements of the load/wiring of your 12v appliances.
the 30A available doesn't mean anything from that perspective.
That is just the total current you are able to pull through the system in total at any one time.
So if you have 6 items pulling say 5A each, you're total would be at the limit of what the converter could supply.
You're wiring would such that it could handle more than the 5A, say 10A wiring and the fuse would be rated under what the wire could handle, say a 7.5A fuse.
The 7.5A fuse covers the maximum current the load will pull at 5A but is lower than what the wire can handle and if things go wrong it will blow before the wire gets near its own limits and ....well catches on fire :)

Hope that all makes sense

cheers Brett

Jaahn · Guru

Hi smile

denmonkey has give some good information to consider. So I will just add to that.

You will need a controller that is at least 20A minimum for the 400W panels at 24V. You might like to get a bigger one so you could add another panel in the future like denmonkey allowed for. He also bought the controller with + remote meter MT50 option, which I also think is very handy. When you go to that ebay site there is a 'drop down' menu at the top which says CURRENT and SELECT. Click on that and there are the current rating for the controller only, then the controllers with a +wifi option, then the controllers with a +MT50 option then the +options only. The 20A controller with the +mt50 option is the tenth one down the list. Click on that and it will then give you the cost of that selection to buy it. Or you could spend a bit more and get the the next one, 30A +mt50. Or what suits you. Read the sellers information further down for more specs etc.

We both suggested you wire the two panels into the controller 'in parallel' . That means you take the two sets of wires from the panels(extended as necessary) and join the two + wires together and then the - wires together and then put them into the controller screw ports where shown. This will run the panels together 'in parallel' at the same voltage. Overall we think this will work best ! Any extension wires you use from the panels to the controller must be big enough, perhaps these are already put there.

I did suggest a different arrangement to charge your vehicle battery and the house batteries but not necessary. Your two lots of panels and controllers would work OK.

My other suggestion is to get LED light globes for the bus that can run off 24V and do that. They are easily found on ebay look for led globes 12/24v. This will leave your 12V converter to use for other things. A lot of phone chargers and the like will run on 12 & 24V DC. Look at the specs before you buy them. Most trucks and buses have 24V systems so there are lots of things made for that voltage if you look.

Before you buy a 12V converter make a list of what you need to run off it at one time. I have got rid of a few I had in the shed but they work well IF YOU DO NOT OVERLOAD THEM. My previous MH and Civilian were 24V but my current one is 12V. hmm

Good luck Jaahn

-- Edited by Jaahn on Thursday 20th of June 2019 11:53:25 AM

-- Edited by Jaahn on Thursday 20th of June 2019 12:11:09 PM

Jaahn · Guru

Hi smile

I thought I would put up this seller's ebay store site just for information. I have bought from them in the past but have no connection. It shows the various Tracer models currently available, and the options of WiFi remote metering and the normal remote meter also. If you have remote metering you do not need a unit with a meter on the front as it should be mounted near the battery so might not be visible anyway. They have an Australian based store and sometimes have a controller for bidding on, if you like a gamble hmm

Other people who might want some information on MPPT regulators who are looking here at this thread might get some information from it. Note I regularly buy things off ebay and generally have had a good run with all my solar stuff. This store also has lots of other solar items for you to look at. wink

https://www.ebay.com.au/str/Domitric/Epever-MPPT-Controller/_i.html?_storecat=3447591819

jaahn

-- Edited by Jaahn on Sunday 23rd of June 2019 05:49:16 PM

Whenarewethere · Guru

I've had up to 11.3 amps output from 120 watts. I had a 10amp MPPT & it didn't put any more than 10amps out. Bought a 20amp MPPT & got 11.3amps. We learn by our mistakes. So get a controller with enough capacity.

My setup: https://thegreynomads.activeboard.com/t65231112/custom-6x20-watts-solar-setup-with-mppt/

T1 Terry · Guru

Before all the MPPT crowd get their hackles up that I'm calling you a liar, I'm not, I'm just trying to show the numbers do not add up.
120 / 11.3 = 10.62v. That would require a 100% conversion factor, something not even the most ardent MPPT supporter will try to propose is possible. I'm guessing your battery was not down to 10.6v when you saw this 11.3 amps so that makes the calculation even more beyond possible reality, so something doesn't add up does it. The catch cry that lithium batteries are not magic must be the same for MPPT controllers, so either the solar is not 120w as the labels claims (6 x 20), or the unit being used to measure the current isn't accurate, or a combination of the two, or magic is a foot.

T1 Terry

Jaahn · Guru

Whenarewethere wrote:
I've had up to 11.3 amps output from 120 watts. I had a 10amp MPPT & it didn't put any more than 10amps out. Bought a 20amp MPPT & got 11.3amps. We learn by our mistakes. So get a controller with enough capacity.
My setup: https://thegreynomads.activeboard.com/t65231112/custom-6x20-watts-solar-setup-with-mppt/

Hmm.. smile

Whatever the figures are, accurate or not, the important thing to learn here is this( as whenarewethere has said !). If the controller has the ability to limit the current to its rated maximum, as most good controllers do, if you undersize it then you will loose any extra when conditions are favourable. In this case the extra 1.3 amps above the controller limit(=13% more). If you go for a bigger rated controller the extra is always there for you if it comes. aww or you add another panel.

I would also say you are better off getting the next size up and running the controller below its maximum rating at all times. It will be more likely to have a happy trouble free long life IMHO. biggrin

Jaahn

-- Edited by Jaahn on Monday 24th of June 2019 01:43:39 PM

T1 Terry · Guru

Full agree Jaahn, the Morningstar engineers say the same thing but more related to heat generation than potential output. An MPPT controller run at a max of 2/3rds capacity and close to the target output voltage will run much cooler and therefore far more efficiently than one close to or exceeding its max output and if it needs to do a major voltage/amps conversion between the incoming voltage and the output voltage.
This discussion came about when I questioned if the newer Morningstar MPPT controllers could hand the over 40*C temps experienced in an Aust summer, limiting the heat generated was the main focus of the engineer's reply. The aim seems to be to avoid both extremes to improve efficiency and heat generation.

T1 Terry

Whenarewethere · Guru

It cost me another $260 for the replacement 20amp controller, at least I have a spare 10amp I can pack as it is small enough, & $50 for heatsinks to squeeze a bit more out of the controller in hot weather. In the meantime I have upgraded the 6AWG lead to 4AWG. This is actually for my air compressors as the 6AWG was too light, but it will double up for the solar panels. Another 0.11% increase in efficiency for the panels!

We like to have our 240volts at home working properly so why not have the 12volt system working as best as it can.

T1 Terry · Guru

How did you get the 4AWG cable into the 50 amp Anderson plug terminals? It's a battle to get 5AWG @ 16.8mm sq into the lugs, no idea how you would get 4AWG @ 21mm sq into that hole?

T1 Terry

Whenarewethere · Guru

The learned virtuosity of bush carpentry cunningness! Stuffed as many wires in as possible & the few remaining wrapped around the cable.

The new cable does not get warm & the compressors take 5.0 seconds instead of 5.5 seconds for the pressure switch to stop.

I would have gone with a larger Anderson plug but that introduces new list of issues. The other idea was to try & expand the lug with a ball punch but I didn't have one at hand. But I might give it a go as I have spare lugs to experiment with. Just have to knock up a jig to hold the lug.

Use the largest cable you can to squeeze as much out of whatever you are building.

T1 Terry · Guru

We ground a long drift punch tapered on the end to open up the same size crimp lugs to make it easier to get the 6 B&S cable in before crimping it with the hydraulic crimper. The Anderson plug lugs are much thinner material though, so a little at a time to avoid splitting it might work. At least the genuine Anderson plug 50 amp lugs have a flared bit at the start of where the cables go in so they are at least easier to get the fine strands in.

Good luck with the lug flaring and maybe a photo if possible? I'd love to be able to run 4 B&S cable into the 50 amp plugs rather than 6 B&S cable when doing the cable run from the start battery to the towbar, that would improve the voltage drop heaps when trying to pull 60 amps through it to the DC to DC charger.

T1 Terry

Whenarewethere · Guru

I drilled a block of wood to the right depth to support the end of the lug & the bottom of the cup. With a bit of grease I first used a Dynabolt which was 6mm at the end & hammered that in. That worked really well & I could wiggle it back out. The next stage was more difficult as I couldn't wiggle the punches out.

Using progressively larger (old) drill bits, I filed a small taper on the back, only needs to be larger by the diameter of the previous size, so 0.2mm at most, & hammered in. It is better progressively work down the cup with larger sizes. Not try to go all the way down with one size then all the way down with the next larger size as that is more difficult to get that punch (drill bit) out because you don't have wiggle room so to speak.

I did have to drill a hole in the piece of metal (make the hole a bit loose) to make a tee handle & put that over the drill bit & then drill bit backwards in a drill to clamp the drill bit, to be able pull the lug off the back end to the drill bit a few times.

Cleaned off the grease & the lugs looked in pretty good shape. Wouldn't want to do this all the time but for the odd 4AWG cable is wasn't too difficult & didn't have to buy any extra tools. Buy a Dynabolt (back end 6mm) if you don't have one, as it would be the worth getting for the first enlargement as the was easy.

The Travelling Dillberries · Guru

Whenarewethere wrote:
I drilled a block of wood to the right depth to support the end of the lug & the bottom of the cup. With a bit of grease I first used a Dynabolt which was 6mm at the end & hammered that in. That worked really well & I could wiggle it back out. The next stage was more difficult as I couldn't wiggle the punches out.
Using progressively larger (old) drill bits, I filed a small taper on the back, only needs to be larger by the diameter of the previous size, so 0.2mm at most, & hammered in. It is better progressively work down the cup with larger sizes. Not try to go all the way down with one size then all the way down with the next larger size as that is more difficult to get that punch (drill bit) out because you don't have wiggle room so to speak.
I did have to drill a hole in the piece of metal (make the hole a bit loose) to make a tee handle & put that over the drill bit & then drill bit backwards in a drill to clamp the drill bit, to be able pull the lug off the back end to the drill bit a few times.
Cleaned off the grease & the lugs looked in pretty good shape. Wouldn't want to do this all the time but for the odd 4AWG cable is wasn't too difficult & didn't have to buy any extra tools. Buy a Dynabolt (back end 6mm) if you don't have one, as it would be the worth getting for the first enlargement as the was easy.

I cant believe you guys are going to all this trouble. If you are doing it for voltage drop reasons, just cut the cores out until it fits in the lug. This will not affect the VD. (have you checked the reduced csa of the lug vs resistance?)

If your doing it for current carrying capacity as in T1's post you are going the wrong way about it. trying to use a cable to carry 60 amps thru a 50amp lug is not advisable. Try a 120amp Anderson that is manufactured for that size cable and the current rating.

Cheers,

Chris.

Whenarewethere · Guru

The 50amp plug can take 120amps using 6AWG cable when not hot plugging.

The Travelling Dillberries · Guru

Whenarewethere wrote:
The 50amp plug can take 120amps using 6AWG cable when not hot plugging.

Where did you get that current rating from Jon, this is the spec from Anderson:

Specification

Amperage Rating:	50
Colour:	Grey
Contact Plating:	Silver
Contacts Supplied:	No
Housing Gender:	Genderless
Housing Material:	Polycarbonate
Mounting Type:	Cable
Oper. Volt (AC):	600
Oper. Volt (DC):	600
Positions:	2
Type:	Complete Kits
Wire Size (AWG):	6

T1 Terry · Guru

I understand what you are saying Chris and you are quite right, a 50 amp plug should only be considered suitable for carrying a 50 amp load. With the 6 B&S cable, to supply the 630w required to the 40 amp DC to DC (14.4v x 40 amps x 10% losses = 633w) with a voltage drop down to 10.5v, the current draw is 60 amps. With bigger cabling the voltage drop would be less, say 12.5v at the input side, 630w / 12.5v = 50.4 amps. That peak load of 630w is only short term at the end of the boost cycle and generally the when charging lithium batteries the BMS would have stopped the charger at 14v, but it would be nice to have that bit more safety margin before the limits were met.
The max limit of 10.5v is the point the DC to DC charger reduces its output current to limit the peak input current to 60 amps, so that is a hard limit, but going up to 120 amp Anderson plugs for such a short term possible overload is a bit of overkill.

T1 Terry

Whenarewethere · Guru

UL1977 standard

The Travelling Dillberries · Guru

So Jon, are you using Anderson "Powerclaw" not the standard Anderson "powerpole"?

Just trying to get a handle on what you are suggesting as I would not like to think anyone would try and use a 50Amp to run a load of 120amps, only thing to come from that would not be good.

The Travelling Dillberries · Guru

T1 Terry wrote:
I understand what you are saying Chris and you are quite right, a 50 amp plug should only be considered suitable for carrying a 50 amp load. With the 6 B&S cable, to supply the 630w required to the 40 amp DC to DC (14.4v x 40 amps x 10% losses = 633w) with a voltage drop down to 10.5v, the current draw is 60 amps. With bigger cabling the voltage drop would be less, say 12.5v at the input side, 630w / 12.5v = 50.4 amps. That peak load of 630w is only short term at the end of the boost cycle and generally the when charging lithium batteries the BMS would have stopped the charger at 14v, but it would be nice to have that bit more safety margin before the limits were met.
The max limit of 10.5v is the point the DC to DC charger reduces its output current to limit the peak input current to 60 amps, so that is a hard limit, but going up to 120 amp Anderson plugs for such a short term possible overload is a bit of overkill.

T1 Terry

Thanks Terry, no mention it was short duration....all good.

Whenarewethere · Guru

As this is getting a bit too off topic I started another thread here:

https://thegreynomads.activeboard.com/t65663515/anderson-plugs-with-oversize-cables-air-compressor-issues/?page=last#lastPostAnchor