Solar - the more I read the less I know

[Lenny HB]

Unless you have some odd wiring turning the fridge to battery won't trouble your solar or habitation batteries as the fridge normally only works off 12 volts coming directly from the vehicle when the engine is running. To do otherwise would simply flatten the habitation batteries in short order. It is possible, when you have a lot of solar to run the fridge from it but the wiring needs to be altered.

All 3 vans we have had you can run the fridge from the leisure batteries.

 

[dathers]

well ended up at 12.63 volts, so definitely not in the greatest of condition, me thinks more tinkering to come.
BTW from earlier post Udo came back to me - no go at 300w, which as a representative of Schaudt I think he would pretty much have to.

"The charger is not able to manage 300W, so the best is to use a second LRM to manage the additional panel up to 270W max.
You can add the solar-panel at the entry additional charger at the EBL where you have normally a fuse with 20A.
With Best Regards,

i. o. Udo Lang."

Whatever I decided on though I won't be going down that route, what happens if I connect the panels in series......

 

[funflair]

well ended up at 12.63 volts, so definitely not in the greatest of condition, me thinks more tinkering to come.
BTW from earlier post Udo came back to me - no go at 300w, which as a representative of Schaudt I think he would pretty much have to.

"The charger is not able to manage 300W, so the best is to use a second LRM to manage the additional panel up to 270W max.
You can add the solar-panel at the entry additional charger at the EBL where you have normally a fuse with 20A.
With Best Regards,

i. o. Udo Lang."

Whatever I decided on though I won't be going down that route, what happens if I connect the panels in series......

Looking at the circuit drawing EBL 101 the additional charger port referred to is BL7 and is indeed fused 20 amps as Udo says, so another solar controller doesn't have to be Schaudt.

Panel in series doubles the volts and the amps stay at one panels output BUT then the controller (if it can handle the voltage) will still output roughly the same volts and amps as in parallel.

Martin

 

[dathers]

thats what I thought, but the LRM 1218 can only handle up to 32 off load volts, if I match my panels they'd be just over 60v. Think I may switch my reg to a victron, I know lots of people are now using votronic, but one thing I've seen Vanbitz and Aandacaravans agree on is victron.
plus victron do have a snazzy bluetooth app interface. But it all costs money - as I said earlier more tinkering to be done before I go with my end solution.
Thanks again for the input.

 

[dathers]

just looking at the victron ppt 75/15 its limited to 220w but has an open circuit voltage of 75v, i think this would probably do for us, 2 * 150 w panels in series, and they claim to have some smart technology that prevents over cycling of the batteries.

^{_{Subscribers  do not see these advertisements}}

 

[dathers]

draw back with the victron though is that it doesn't do dual charge, so would need to run a battery master too

 

[funflair]

Votronic dual outputs and let it run your fridge via AES trigger when you have a roof full of spare sunshine.

Martin

 

[dathers]

ok you got me, I now need to dig around those magic words AES trigger

 

[funflair]

ok you got me, I now need to dig around those magic words AES trigger

an output terminal on Votronic controllers that sends a AES signal that switches a fridge with S+ to run on 12volts (so from your habitation batteries) just like the D+ from the alternator does when you start the engine, it is also possible to switch older pre S+ fridges but you need a diode on the D+

Martin

 

[dathers]

so we have a dometic RMDT 8555, and yes it has S+ capability, doubt though with my puny setup I'll get to the 'spare solar' state, but one to keep in mind.
BTW if I did go down that route, assume I'd have to wire directly through to the fridge?

^{_{Subscribers  do not see these advertisements}}

 

[tonyidle]

Battery capacity quoted by manufacturers is based on a specific test load. The 'standard' test load is set to discharge the battery at the "20 hour rate". So, for example, a 100Ah battery would be tested with a load that would draw 100/20=5A. If you use a heavier load (like your fridge) you should not expect it to last for 100/14 hours - it will discharge much more quickly than the Ah capacity would suggest.

"
Let’s consider a flooded wet cell lead acid battery that has 20 hour discharge rating of 100 amp hours.

Based on this specification, we know that this battery will supply 5 amps for 20 hours while maintaining a voltage that is above 10.5 volts.

If we were to increased the discharge rate to 10 amps, we might erroneously concluded that the battery will last for 10 hours.

Using the equation for Peukert’s law as shown below, we find that the battery will last significantly less than 10 hours.

NOTE – In order to solve this equation we’re going to need to know what the Peukert’s exponent is. For a flooded battery, its typically going to be somewhere between 1.2 and 1.6. For this example, we’re going to use 1.4.












What is Peukert Exponent for Your Particular Battery
It’s different from battery to battery. Worse, many manufacturers do not readily publish a Peukert’s exponent. That said, there are some general ranges for the different kinds of lead acid batteries that can be used for estimation purposes.

• AGM batteries range between 1.05 and 1.15
• Gel batteries range between 1.1 and 1.25
• Flooded batteries range between 1.2 and 1.6

If more accurate estimates are required, it is possible to calculate the Peukert exponent from most battery manufacturer specifications. Stay tuned for another article.

Peukerts Law Limitations
Peukert’s law is a valuable tool for estimation. However, it has limitations. Among them are…

• The affect that temperature has on batteries is not included in the equation.
• Battery age is not considered. The Peukert exponent increases with battery age.
• If you’re calculating for a low discharge rate, the equation does not account for the fact that each battery has a self discharge rate.

All that said, in terms of estimation, Peukert’s law gets us much closer to estimating real world performance of a battery than simple extrapolations of the amp hour rating.


Let’s consider a flooded wet cell lead acid battery that has 20 hour discharge rating of 100 amp hours.

Based on this specification, we know that this battery will supply 5 amps for 20 hours while maintaining a voltage that is above 10.5 volts.

If we were to increased the discharge rate to 10 amps, we might erroneously concluded that the battery will last for 10 hours.

Using the equation for Peukert’s law as shown below, we find that the battery will last significantly less than 10 hours.

NOTE – In order to solve this equation we’re going to need to know what the Peukert’s exponent is. For a flooded battery, its typically going to be somewhere between 1.2 and 1.6. For this example, we’re going to use 1.4.

What is Peukert Exponent for Your Particular Battery
It’s different from battery to battery. Worse, many manufacturers do not readily publish a Peukert’s exponent. That said, there are some general ranges for the different kinds of lead acid batteries that can be used for estimation purposes.

• AGM batteries range between 1.05 and 1.15
• Gel batteries range between 1.1 and 1.25
• Flooded batteries range between 1.2 and 1.6

If more accurate estimates are required, it is possible to calculate the Peukert exponent from most battery manufacturer specifications. Stay tuned for another article.

Peukerts Law Limitations
Peukert’s law is a valuable tool for estimation. However, it has limitations. Among them are…

• The affect that temperature has on batteries is not included in the equation.
• Battery age is not considered. The Peukert exponent increases with battery age.
• If you’re calculating for a low discharge rate, the equation does not account for the fact that each battery has a self discharge rate.

All that said, in terms of estimation, Peukert’s law gets us much closer to estimating real world performance of a battery than simple extrapolations of the amp hour rating."

 

[Lenny HB]

so we have a dometic RMDT 8555, and yes it has S+ capability, doubt though with my puny setup I'll get to the 'spare solar' state, but one to keep in mind.
BTW if I did go down that route, assume I'd have to wire directly through to the fridge?

You only need to run a thin signal wire to the S+ on the fridge, German vans are normally set up to run the fridge off the habitation batteries.

I have 300 watts of solar an RMDT8501 fridge and have the S+ terminal wired to the Votronic AES output, in Spain in mid march through April on a good clear sunny day the fridge would run for an hour sometimes 2 not a lot but when the sun is higher should be a lot longer.

You have to take into account the fridge is stupid, Dometic in their wisdom have set 12v Solar as the 1st priority in the energy selection order. Like @sallylillian, I found out this, when you are on EHU the fridge if set to AES switches to 12v. This is because when you are on EHU once the batteries are charged the Votronic unit sees this and and it switches the AES trigger on, the dumb fridge sees the signal and because of its energy source order it switches to 12v.
Easy to get around the problem, I have temporarily fitted a switch in line with the AES output on the regulator so I can O/C the AES connection when on EHU, if I get around to it I may fit a mains powered relay so it opens the circuit when on EHU not a priority as we rarely use EHU.

As for wiring your panels in series I would say with parallel, although series is slightly more efficient if one panel is in shade you will loose the output from both panels, in parallel with one panel in shade you will still have output from the other panel. The benefits of the panels in parallel far outweighs any disadvantages on a Motorhome.

 

[dathers]

Thanks Tony, I started off down a similar route when I first installed the BMV 700, as I wanted to set up the correct peukert value, the BMV 700 manual give this equation for finding the peukert exponent:

where t2 = 20hours and t1 = 5hrs (these figures are provided on the varta tech sheet)
and I1 = 17amp (the 5hr discharge rate) and I2 is the 4.75 the 20hr rate
so working through that I get a peukert of 1.087 - with all the caveats you posted above.

 

[dathers]

thanks martin, parallel it will be didn't realise the impact of shading when in series

 

[dathers]

ok so been to the MH, not be sunny here today, mixture of dull and slightly brighter moments but as yet no direct sunlight, at 2pm I'd drawn 12ah from the solar to recharge the batteries, not sure if thats good or bad from a flat semi flex 150w panel

^{_{Subscribers  do not see these advertisements}}

 

[funflair]

You only need to run a thin signal wire to the S+ on the fridge, German vans are normally set up to run the fridge off the habitation batteries.

I have 300 watts of solar an RMDT8501 fridge and have the S+ terminal wired to the Votronic AES output, in Spain in mid march through April on a good clear sunny day the fridge would run for an hour sometimes 2 not a lot but when the sun is higher should be a lot longer.

You have to take into account the fridge is stupid, Dometic in their wisdom have set 12v Solar as the 1st priority in the energy selection order. Like @sallylillian, I found out this, when you are on EHU the fridge if set to AES switches to 12v. This is because when you are on EHU once the batteries are charged the Votronic unit sees this and and it switches the AES trigger on, the dumb fridge sees the signal and because of its energy source order it switches to 12v.
Easy to get around the problem, I have temporarily fitted a switch in line with the AES output on the regulator so I can O/C the AES connection when on EHU, if I get around to it I may fit a mains powered relay so it opens the circuit when on EHU not a priority as we rarely use EHU.

As for wiring your panels in series I would say with parallel, although series is slightly more efficient if one panel is in shade you will loose the output from both panels, in parallel with one panel in shade you will still have output from the other panel. The benefits of the panels in parallel far outweighs any disadvantages on a Motorhome.

That’s really strange although I did read it when Michael discovered it, ours being only D+ takes the EHU as priority and then the solar kicks in over gas when no EHU so you could try it Hooked up to the D+ with a diode on the D+ Engine signal wire and then it should behave the same as starting the engine.

Martin

 

[Lenny HB]

That’s really strange although I did read it when Michael discovered it, ours being only D+ takes the EHU as priority and then the solar kicks in over gas when no EHU so you could try it Hooked up to the D+ with a diode on the D+ Engine signal wire and then it should behave the same as starting the engine.

Martin

Looking at the EBL diagram when the D+ relay is on the fridge is connect to the starter battery & disconnected from the leisure battery.

 

[funflair]

Looking at the EBL diagram when the D+ relay is on the fridge is connect to the starter battery & disconnected from the leisure battery.

Ah of course EBL will have a look later we are CBE

Martin

EDIT @Lenny HB yes looked at a EBL diagram and agree, so when the D+ is not live then habitation power is at the fridge and the S+ can turn it on to 12v, is your S+ at the fridge rather than EBL? I must double check ours as I know it runs of the leisure when forced at the fridge and assume the same on D+ but must check when it next kicks in.

Martin

 

[Lenny HB]

Yes the S+ is on the back of the fridge.

Turned my fridge on a couple of hours ago (on AES) it has been running on 12v, battery 14.08v, current -0.2a fridge draws around 14 amps so its working well when there is a bit of sun.

 

[funflair]

Checked ours this morning and it’s running on D+ from the leisure for sure, I think ours is wired “stand alone” so everything comes from the leisure batteries.

Martin

^{_{Subscribers  do not see these advertisements}}

 

[Nasher]

Some amazingly good, informative and detailed information on this thread.

That said, forget solar & buy a generator - far less complicated, works in the dark and you will get lots of attention from all the other motor-homers/caravaners/Campers.

 

[dathers]

Got that too, you can tell I've just retired and finding things to play with.

 

[Ivory55]

Some amazingly good, informative and detailed information on this thread.

That said, forget solar & buy a generator - far less complicated, works in the dark and you will get lots of attention from all the other motor-homers/caravaners/Campers.

We brought a generator, it’s cheaper to buy then the other stuff and you can sell it separate from the van.

 

[Bre]

I used to think I was bright enough, but after reading this and trying to see if the solar on my newly purchased MH are working, I realize I am a complete imbecile

 

[TheCaller]

thanks martin, parallel it will be didn't realise the impact of shading when in series

If you can avoid parking where partial shading will be a problem, then you will get more out of your panels when in series. Remember that includes anything on your roof that might cast a shadow on a panel.

If you are in a situation where a little charge on a dull UK winter's day is better than nothing, then series connection is worth considering. If your van spends the winter on your drive with access to EHU, then there will be little or no benefit.

^{_{Subscribers  do not see these advertisements}}

 

[Beemobile]

Five generators stolen week ago yesterday at Malvern show ground, take care.

 

[dathers]

there are some real bar stewards around, wonder whats the best way of securing your generator, simple but solid motorbike chain lock?

 

[Beemobile]

Take it to bed with you

 

[Nasher]

there are some real bar stewards around, wonder whats the best way of securing your generator, simple but solid motorbike chain lock?

I always carry a motorbike lock & chain anyway (for my motorbikes, believe it or not!), so use that looped around something secure under the van.

Although, frequently I recharge the batteries when back at the van having lunch, so I'm about.

 

[Harvard]

As for wiring your panels in series I would say with parallel, although series is slightly more efficient if one panel is in shade you will loose the output from both panels, in parallel with one panel in shade you will still have output from the other panel. The benefits of the panels in parallel far outweighs any disadvantages on a Motorhome.[/QUOTE]

^{_{Subscribers  do not see these advertisements}}