Motorhome Solar Power System Issue

[fluffyboxerfan]

Hi there, I was hoping someone could help regarding an issue we are having with our motorhome's solar power system. We are running 2 x 250w house panels,a 40amp MPPT controller,3 x 130amp AGM batteries, and a 3000W inverter. We are continually drawing 2amps, (running gas detectors, fridge management system, hot water management system.) The biggest draw we have is our microwave which draws 150amps (but only in use for 2 - 4 minutes. once or twice a day). We have LED lighting at night and usually only have the minimum on. We run the fridge on gas unless on 240 power. The inverter is only switched on when needed so is not drawing constantly. When the vehicle is stored and not in use the batteries are isolated and are trickle charged by a Projecta Intelli-power battery charger.(12V 7 stage switchmode), which is up to a minimum of 2 weeks or longer at a time, so I would assume that the batteries would be fully charged.

We installed the system 2 1/2 years ago and actually designed the system around running our microwave for short intervals a couple of times a day, and all was going well and getting plenty of power up until a few months ago.

For the last couple of months we seem to be running low on power in the mornings, in fact the meter is reading only half charged first thing up. During the day the panels are putting in around 24 amps and by the afternoon says the batteries are fully charged and it only puts in around 0 amps to 4 amps. We have an amp gauge on the house batteries so we know what we are drawing at all times. While the solar panels are putting in power there is no issue with the usage at all. It will even run the microwave after a few hours of solar charging. But the main concern for us is all of a sudden we seem to be losing our power during the night and have no clue as to why. With each day away the system just doesn't seem to catch us with power storage, in fact after 4 days away the batteries wouldn't even start our onboard generator.

We have load tested the batteries individually and all tested fine. The MPPT controller tested as it should have as well. We have had an electrician check the system and as far as he could tell everything checked out OK. My thoughts are perhaps the battery charger is not up to scratch when we leave home, hence the batteries are not fully charged. Or perhaps there could be a problem with the batteries, or are we just expecting too much out of our system.

If anyone has any suggestions or thoughts as to what could be the reason it would be greatly appreciated.

 

[condor22]

Fluffy, I'll have another read later tonight, I've only just got back from a week away and have clean up etc. I'll have a think about it..

 

[PabloP]

Hi there, I was hoping someone could help regarding an issue we are having with our motorhome's solar power system. We are running 2 x 250w house panels,a 40amp MPPT controller,3 x 130amp AGM batteries, and a 3000W inverter. We are continually drawing 2amps, (running gas detectors, fridge management system, hot water management system.) The biggest draw we have is our microwave which draws 150amps (but only in use for 2 - 4 minutes. once or twice a day). We have LED lighting at night and usually only have the minimum on. We run the fridge on gas unless on 240 power. The inverter is only switched on when needed so is not drawing constantly. When the vehicle is stored and not in use the batteries are isolated and are trickle charged by a Projecta Intelli-power battery charger.(12V 7 stage switchmode), which is up to a minimum of 2 weeks or longer at a time, so I would assume that the batteries would be fully charged.

We installed the system 2 1/2 years ago and actually designed the system around running our microwave for short intervals a couple of times a day, and all was going well and getting plenty of power up until a few months ago.

For the last couple of months we seem to be running low on power in the mornings, in fact the meter is reading only half charged first thing up. During the day the panels are putting in around 24 amps and by the afternoon says the batteries are fully charged and it only puts in around 0 amps to 4 amps. We have an amp gauge on the house batteries so we know what we are drawing at all times. While the solar panels are putting in power there is no issue with the usage at all. It will even run the microwave after a few hours of solar charging. But the main concern for us is all of a sudden we seem to be losing our power during the night and have no clue as to why. With each day away the system just doesn't seem to catch us with power storage, in fact after 4 days away the batteries wouldn't even start our onboard generator.

We have load tested the batteries individually and all tested fine. The MPPT controller tested as it should have as well. We have had an electrician check the system and as far as he could tell everything checked out OK. My thoughts are perhaps the battery charger is not up to scratch when we leave home, hence the batteries are not fully charged. Or perhaps there could be a problem with the batteries, or are we just expecting too much out of our system.

If anyone has any suggestions or thoughts as to what could be the reason it would be greatly appreciated.

Fluffy, to start with there is something way out of whack with your microwave info of 150amps, as that is way over what a microwave uses, 5 amps would likely to be closer to the figure for a decent microwave, so it could be that there is something screwy with the measurement system or process.

You seem to have a decent sized battery bank at almost 400ah, and the solar bank seems ok at 300w, but a bit low to bring the batteries up timely if they have been significantly discharged. I aim for full charge by noon on a normal sunny day.

That inverter is a big one, and they are inefficient beasts, but if only running for the microwave that shouldn't be causing the problem.

Remember that the lower a battery bank is discharged and the frequency and depth of the discharge impacts the battery life.

Do you have the batteries boosted from the vehicle alternator as that would normally give a good charge is driving for a few hours.

I suspect that one or both of the batteries are faulty, but without some independent testing is required, versus what the built in monitoring system is showing as I am concerned that it is providing data that should be questioned.

You need to measure the current drain during the day and the night, to try and determine what is causing the excessive voltage drop.

Rob.

 

[condor22]

Pablo,

I have to disagree with the microwave logic.... Fluffy is using it on an inverter, but, he doesn't say what wattage it is. However, my microwave is a small one of about 850W output , but uses nearer 1100W of input power.

So 1100W @ 240VAC is about 4.6A, on that you are correct. BUT and it is a BIG but.....

When running on an inverter you need to divide the same 1100W by the input voltage which is nominally 12VDC, which is a bit over 91A, but probably over 95A with efficiency loss. This means that for every 5 minutes of microwave use, the battery discharges at least 7.7AH. Then it's plus the 2A per hour used which is 48AH per day, totalling over 50AH then there's lighting, etc.

390AH of batteries (which I assume are the 3 x 130AH in parallel) should be more than enough. However, if the batteries are going flat, there are 2 main reasons to look at first. either the batteries are not getting enough charge, or, they are not holding the charge. The trouble with 3 paralleled batteries is that if one is stuffed, the whole system is stuffed. I'll write a bit more tomorrow, it's getting late........

Late thought - Or, another possibility is there is a current leak that is not being monitored.

 

[PabloP]

You got me there Condor, too late at night. At about 4am this morning my sub-conscious woke me up and said "richard cranium", it was 150a at 12v, not 240. So I did some quick maths in my head and worked out that 150 x 12 = 1800watts. If the inverter was running at about 40> 50% efficiency then that would relate to a 1000W microwave, which is not unusual.

So here I am writing this at 6am as I could not get back to sleep (DH).

I was thinking that if the microwave was being used at night, or when there was no opportunity to recharge the batteries, then over time this would result in battery deterioration more quickly than would be normal. Plus I was wondering if there was a diesel heating system, running at night (hot water, stove, room heater), like we both know about, as they really chew the juice during the glo-plug starting phase and a lesser amount when up and running.

So one or more batteries may be losing the ability to hold a charge and drawing the others down overnight. As a quick fix perhaps run the vehicle motor while using the microwave, will offset the drain a bit and see what impact this has on the morning voltage/charge remaining.

I will leave it up to you to work this one out.

Rob.

 

[Nightjar]

Do you burn the midnight air watching TV or movies, have you bought a new entertainment system or checked the amp draw?
As you have said your batteries are draining overnight is there any back feed leaking through your panels?
Or as already mentioned one or more of your batteries have crook cells.

Lots of reading here.

http://www.fridge-and-solar.net/index.htm

 

[fluffyboxerfan]

Thankyou Nightjar,

No do not use any excessive power at night, only LED lights usually. water pump for shower and diesel heater occasionally, but the system has usually handled this load with no problems in the morning.
Will have to check into leak back to panels, but wouldn't have a clue as as to how to go about it. I think our MPPT system takes care of that though.
We are running a Tracer-4210RN series controller with a Remote Meter : MT5. connected via an RJ45 port on the Tracer.
Am getting the batteries checked at a Battery Power store locally in the next few days, but all test so far conducted by myself and electrician are showing they are fine.
Very perplexing indeed.

Any other suggestions are welcomed? This problem requires more knowledge of these issues than I have unfortunately.

 

[fluffyboxerfan]

Thankyou Condor and Pablo for your responses.

I shall attempt to answer your queries as best I can. I certainly am not well versed with all of this, but shall do my best.
The microwave has a 1200 watt input rating. The system was tested by an electrician using a 12V amp gauge on the lead from the battery bank (in parrallel) to the inverter while running the microwave.(so I gather it was reading the complete draw at the time of testing). which measured at 150amps. (microwave+2amp cont.use)

The baintech volt/amp meter (BTBM0010R) I have been using, that is installed (I have only just found out since the electrician's testing) will only read up to 50amp without going crazy and jumping all over the place.

Ran the inverter and microwave several times to put a fairly large draw on the battery bank, then re-tested the batteries with a battery tester and they still tested as good?

I am going to take the 3 batteries into a local battery power store to have an independent load test done on them, just to make sure there is no problem with them.

The batteries are charged whilst driving from the alternator, which is also perplexing they should have been fully charged when we left home plus charging over the 6 hr drive. We then stayed put for 24hrs, then drove about 1 1/2 hours and then stayed put for 2 days, before driving another 3 hrs and stayed overnight, then drove 61/2 hrs home. All 4 days we had mostly full sun on the batteries.

One theory I am wondering about is perhaps my charger is not putting in enough of a charge to completely restore the battery bank to full capacity whilst on 240 power and isolated in the shed at home.

I have a "Projecta Intelli-Power 12volt, 7 stage switchmode model IC700".

Specifications:
Type 7 stage
Input (nominal) 240VAC, 50HZ
Input Power 216W
Output Voltage 12V
Output Current 7A
Miniumum Start
Voltage 2.5V
Back Drain 1 mA

Charge Control:

Desulphation High Frequency Pulse charge up to 11V
Soft Start 3.5A up to 12V
Bulk 7A up to:
14.4V (AGM) (*has the figures for other batteries but this is the rating for ours AGM)
Absorption Constant voltage until current drops to 1.05A
Equalization
(Calcium mode only) Constant current (2.0A up to 16V then hold for 1hr or 12 hr timeout. (I think N/A)
Analysis Monitor battery for 90 sec
Recondition Constant current (1.05A for 4 hours limited to: (14.4V (AGM) (*)
Float 13.7V

Power Supply:
Set Voltage 13.8V DC
Maximum Current 7A

Battery Range:
Deep Cycle 50 - 140AH
Automotive 300-800CCA
Marine 350-900MCA

Not sure if this is of any help, but the Battery Range of Deep Cycle 50-140AH - is this sufficient to recharge 390AH of batteries on trickle charge?

Bill

 

[blisters]

The trickle charge is voltage based and would be using the same output circuit as the bulk charge so there shouldn't be an issue there in regards to current supply. As a first step I would fully charge the batteries then disconnect them from the circuit and each other. Leave them 24 hours then measure the voltage across each of them to verify they are the same and at near full charge. They should be measured at the same temperature so make sure one is not in the sun an the others shade. That will eliminate a battery issue.
Jon

 

[condor22]

Fluffy FYI - There is a calculation that is available online re solar panels v batties v sun hours. Firstly Sun Hours can vary from a bit over 8 hrs per day to as low as 2.6 depending upon location and time of year. There are a few ways to look at this;

• Do I go only north and only in summer?[/*]
• Do I go in all places at all times of the year? or,[/*]
• Do I go south in winter mostly?[/*]

For my part I would design for worst case scenario which is south in winter, i.e. The VIC goldfields in winter. The other way is to be a little less concerned and top up from a small generator or the vehicle engine, occasionally. However, if you have a self contained motorhome and want to be truly fully independent, then worst case scenario is the design criteria. The calculation for the number of panels;

Daily Amp Hours (AH) used x 21.8 / Peak Watts of the panel (PW) / Sun Hours (SH) or (((AH x 21.8)/PW)/SH)

A 120W panel typically outputs about 8 Amps max, which multiplied by 12 = 96 watts, however the output V is higher therefore so is the Watts. To play safe I use a rule of thumb that a 120W panel will safely output about 100 Watts (Max) to a battery. So using the above formula and assuming a 50AH usage in winter in the Vic GT;

= 50 x 21.8 / 100 / 2.8 = 3.89 or to round up 4 x 120W panels. Conversely if you are more north in summer (I'll use 6 sun hours);
= 50 x 21.8 / 100 / 6 = 1.8 or rounded up 2 x 120W panels, which is half the previous panel quantity.

So you can see how important it is to consider where and when you go.

The other calculation is how much battery do you need? The industry advice is AH used x 13, so in the above example that is 50 x 13 = 650 AH. This is the best case scenario to maximise battery life, however in my opinion it is overkill. I prefer to use maximum AH used x 4, which is a nominal 25 % depth of discharge. If you want a bit of Fat then x by 5 or 6 i.e. 50 x 5 = 250 to 300 AH.

I have 1 x 120 AH battery and 2 x 100W panels which gives me a bit over 45 AH of usage. I have a caravan and don't use a big inverter for the microwave, I do use a Diesel Heater, TV, LED lights, pump etc. My average use is about 35AH a day. As I prospect in VIC, in Winter, theoretically I have enough solar input and battery to never run out. I've recently installed these panels and have yet to do the first trip, which will be in about 5 weeks to the VIC GT.

More re Amps

 

[Tathradj]

May be of some help.
Always remember,
.
" A bit of load will tell the story. "
.
What I do to test a battery,
12v only.
Utilize a 100 watt light bulb.
Connect a volts meter across the battery first.
Record the voltage.
Then connect the light bulb across the battery.
let it run for 1 hour.
record the voltage and compare the two.
If you need more brute force,
Use two light bulbs.
Take safety into consideration as things especially the bulbs will get hot.
Beware of sparks and gas.

 

[Tathradj]

I don't hold much faith in a 1 minute battery test.
Though it will show up a really bad stuffed battery
that looses it's float charge real quick.

 

[condor22]

Re your Amp Meter - My first caravan was fitted with a Plasmatronics PL20 solar controller, which had a LED read out of Amps IN/OUT. It was rated to 20 Amps max.
I also had a 300W inverter which at full use is rated to about 27 Amps. So the Inverter bypassed the PL20 as it would overload it. I could only assume AH by knowing what I was running and for how long, so a calculated approximation.

If you want to measure everything that draws current, you need to fit a SHUNT into the inverter circuit. It should be fitted between the inverter and the battery.

A shunt is in simple terms a large chunk of metal that absorbs the high current and then measures the millivoltage drop over the length of the shunt when current flows. It then, using the correct gauge, shows that as Amps. Check your controller to see if it has a Shunt input, if not you may need to find a replacement that will.

Do a search on Google @ Jaycar for examples and Google for the principles of use.

Re charging at home, the rule of thumb I use - Charger Amps max = between 10 and 20% of battery capacity, which for your batteries should be 40 to 60 Amps.

Example, my charger is a Plasmatronics 15A 7 stage, my battery is a 120AH AGM which is 12.5% (I originally had a 100AH battery which charged at 15%, so it is still in the 10-20% range.

Rule = Charge too quick, you cook the battery, charge too slow, they never properly charge. Check the link below, this is what you should fit to your motorhome. (or similar)

http://www.homeof12volt.com/shop/in..._id/c697bb8729221be66f435df502c1740f/offset/0?

 

[silver]

There can sometimes be a quick and simple fix to these types of problems ,... sometimes it's as easy as changing the choice of parking space,
as this

can quite often, and quite quickly
lead to this

and so it's sometimes just a case of making the panels
look like this

just thought no one had yet mentioned the old clean panels trick yet ! 8) :lol:

 

[fluffyboxerfan]

Providing my batteries pass a proper load/voltage check, would adding another battery of the same brand etc., achieve any difference? (Although it would be 2 years 3 months newer).
I had a feeling that perhaps the battery charger was not fully charging them to capacity, so looks like I may have to invest in a new charger.
I have been reading Condor's earlier posts on setting up solar etc., (I certainly have a lot to learn) So very informative and in detail. I read a bit too late last night/morning so it was a bit much to take it all in at once and had to go to bed.
Like Pablo had volts/amps etc., running around in my head most of the early morning, so sleep evaded me for most of the early hours.
But unlike Pablo I couldn't come up with much.
Thankyou for the link Condor, I didn't even realise until looked at the specs that my charger was probably only okay for 1x130 ah agm battery, was told by the dealer that it was good one, although when I purchased it I honestly can't remember If I had decided to run the 3 batteries. I was toying with just 2 for a while and I bought the battery charger a good 6 months before the batteries and set up the system(my old one had died anyway).

 

[fluffyboxerfan]

Thanks Silver, I had thought of that myself but the panels and whole van in fact is washed after every trip and then stored in the shed for a maximum of 4 -8 weeks before the next trip out, so they should be clean before we start. Although maybe a slight layer of dust.

 

[blisters]

Your system used to work so assume for now it is sized ok. I wouldn't worry about your charger just yet. If your batteries are about 50% discharged then a 7 amp charger should have them back up to capacity in three days well within your two week minimum. These should be charged in parallel.

An extra battery won't fix the problem. Your issue is either battery condition, charge or discharge. As you have an amp meter on the batteries what is the discharge at night time? This will tell you if you have excess leakage than what you expect. For example one of your devices reverse current protection may have failed allowing discharge back through the unit e.g. mppt. Make sure the batteries are good by measuring the individual battery rest voltage after charge and overnight use. Leave four hours rest with each battery totally disconnected after overnight. Then it comes down to whether your system is charging enough and at 24 amps it sounds as though it's reasonable.

To me it sounds like either a battery failing or a current leak but you need to verify the easy bits first.
Jon

 

[Tathradj]

One of the reasons why I used to remove the blocking diodes from the back of the
panels and mount them inline close to the controller.
Seen many a weird fault caused by a cracked/failed diode. LOL

 

[blisters]

Yep sounds like something has changed. Fluffy have you tested that the alternator is actually charging the batteries?
Jon

 

[Nightjar]

Have you considered wiring your panels in series?

https://www.victronenergy.com/blog/...ar-modules-to-the-new-mppt-charge-regulators/

https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/