Odd Question MPPT Solar charger with LCD Display...... (1 Viewer)

[jo10000_6]

Odd question, but can a MPPT solar controller with LCD display work (initially) without solar and fundamentally be a battery monitor or does it need the solar connection to complete the link and make everything work?

Without knowing the answer about the solar connection it seems to me it could give you lots of useful information on the battery - voltage, charging current, discharging current etc.

Its not that I don't want solar - I do but Id like to get an idea of what's going off first and buying a good battery monitor then getting solar display thing seems like spending money unnecessarily if the solar kit will do the same and you end up having solar.

Motorhome novice here - be gentle.
Electronics dunce - be even gentler !

 

[Figaro]

My new votronic mppt 250 duo and display is powered from the hab batteries and you do need the controller to be fitted, you can't just have the display.
So display panel works without the solar panels but not controller, is that what you meant ?
BTW I've been very impressed with it so far even though sunshine is very limited. It does seem to be a big improvement on my old schault controller.

 

[jo10000_6]

Hi Figaro

Yes that’s what I meant.

Jo

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[Figaro]

I`ve not got and never had a battery monitor so I`m not sure what they show, maybe more than the solar controller display ?

 

[Pausim]

My Votronic MPPT display shows voltage only when the panels are not connected. When the panels are running it shows what they are producing e.g. Amps, AH, Volts but does not show what is going into the battery. Your domestic 12V system could well be using some, most or all of the power produced by the panels. If you want to know what is going into and out of your battery you need a battery monitor.

 

[Minxy]

You don't have to spend a lot on a battery monitor if all you want to do is see what's in your batteries ... you can get all sorts of cheap ones, I've just wired in one of these to our cab battery as I already had it:

For our hab battery I just stick one of these in a socket:

You can also get one that shows both cab and hab batteries levels:

There are loads and loads of monitors on Ebay so have a shuftie and see which meets your needs.

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[autorouter]

The solar controller will show the battery voltage, and will also show the amps produced by the panels. They only show the values as you look at them, there is no historical counting of amp-hours into and out of the battery. Also they can not show the amps taken from the battery by the loads, or the amps going into the battery from the mains charger, engine alternator, etc.

There are many devices that are called battery monitors. Simple ones as in @MinxyGirl's post, just show the battery voltage at the time.

Slightly more complex ones show the voltage and the battery current. Exactly what current it measures depends on where exactly you fit the 'shunt'. At the battery negative post is the usual place, to measure everything going into and out of the battery.

The best ones measure volts, and have a shunt to measure amps, but also have a built-in computer and clock that keeps a count of the amp-hours into and out of the battery, displaying the running total as a percentage of the battery capacity.

So it depends what information you want, and how much you want to spend. If you need even more information, there's a long detailed article. It's American, it's about batteries in boats, but it applies to a motorhome just as well:
https://marinehowto.com/installing-a-battery-monitor/

 

[Guigsy]

As mentioned by @autorouter the voltage doesn't give you the full story. If you've got solar, you don't really know what your resting voltage is until the sun goes down... and only then if you aren't pulling any significant current from it.

I've just installed a Victron BMV battery monitor that watches the voltage and the current flow. It's smart enough to know charge efficiencies and can differentiate between static voltage on the battery, and when it's been propped up by a solar panel or alternator...

I'll be using it in anger for the first time this weekend.

 

[jo10000_6]

Thanks guys for the last two message - I fitted a battery monitor this week and currently seeing what my battery is doing.

I’m hoping it will be useful.

Thanks
Jo

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[Figaro]

Which one did you buy ?

 

[Guigsy]

Which one did you buy ?

I went all-out and got the Victron BMV 712... I'm a gadget freak and wanted the Bluetooth.

I only fitted it last weekend, so I've not actually used the van yet to find out if it does its job. Thoughts so far is that it's easy to fit. The hardest bit is the shunt has screw-down terminals on each end... and they are LARGE. I've got ring crimp connectors, but I had to drill one out a bit to get the diameter to fit over the terminal. It's obviously over engineered to cope with massive currents and voltages, so I'm not too worried with my little battery setup. The unit display is pretty discrete, but that also means it's pretty small and it's just a backlit multi-segment display rather than a LCD matrix. Fine for displaying numbers in normal use, but if you ever want to play with advanced settings (probably not) then it's a bit of faff. I'll be using the app most of the time (until I work out how to connect it via Bluetooth to my Raspberry Pi campervan monitor... but that's another project).

If I didn't want the Bluetooth bit, I'd probably have got one of the Nasa Marine BM battery monitors.

 

[Pausim]

I went all-out and got the Victron BMV 712... I'm a gadget freak and wanted the Bluetooth.

I only fitted it last weekend, so I've not actually used the van yet to find out if it does its job. Thoughts so far is that it's easy to fit. The hardest bit is the shunt has screw-down terminals on each end... and they are LARGE. I've got ring crimp connectors, but I had to drill one out a bit to get the diameter to fit over the terminal. It's obviously over engineered to cope with massive currents and voltages, so I'm not too worried with my little battery setup. The unit display is pretty discrete, but that also means it's pretty small and it's just a backlit multi-segment display rather than a LCD matrix. Fine for displaying numbers in normal use, but if you ever want to play with advanced settings (probably not) then it's a bit of faff. I'll be using the app most of the time (until I work out how to connect it via Bluetooth to my Raspberry Pi campervan monitor... but that's another project).

If I didn't want the Bluetooth bit, I'd probably have got one of the Nasa Marine BM battery monitors.

Good choice, I bought the BMV 700 and ended up buying the bluetooth dongle to upgrade it within weeks. The app is so much more convenient for daily use. I haven’t even bothered to mount the display in the living area, I have put it in with the battery compartment. I can access the display if I should ever need to change the detailed settings but for day to day use the app has all I need.

I rejected the NASA one despite the clearer display because it lacked the detailed settings for different battery types and I have LiFePO4, which has higher efficiency and a lower Peukerts factors.

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[two]

Do you have to guess the Peukert exponent? I've not yet found a supplier that could tell me. Most don't seem to have even heard of it.

 

[Guigsy]

Do you have to guess the Peukert exponent? I've not yet found a supplier that could tell me. Most don't seem to have even heard of it.

I was under the impression that for lead-acid batteries, the defaults are normally fine. Only if you've got some funky battery chemistry (like LiFePO4) do you need to worry.

 

[Pausim]

I was under the impression that for lead-acid batteries, the defaults are normally fine. Only if you've got some funky battery chemistry (like LiFePO4) do you need to worry.

Victron say the default Peukerts exponent of 1.25 suits most lead acid batteries and to use 1.05 for LiFePO4. For charge efficiency the default is 95% with 99% recommended for LiFePO4.

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[Pausim]

I found this article if you want to know more about Peukert’s law:
http://all-about-lead-acid-batterie...amentals/peukerts-law-and-exponent-explained/

Helpfully it suggested the following values for the different types of lead acid batteries:

• 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

 

[Lenny HB]

Do you have to guess the Peukert exponent? I've not yet found a supplier that could tell me. Most don't seem to have even heard of it.

Exide give 1.1 for their gels, I have Sonnenschine gel almost identical to Exide. When I fitted my BVM I set it to 1.25 as the batteries were over a year old and the Peukert Exponent rises with battery age.

 

[two]

I found this article if you want to know more about Peukert’s law:
http://all-about-lead-acid-batterie...amentals/peukerts-law-and-exponent-explained/

Helpfully it suggested the following values for the different types of lead acid batteries:

• 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

Suggests that you need to be more precise for flooded cells.
I was lucky enough to find someone at Exide who could spell Peukert, but they still couldn't tell me what value to use.

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[jo10000_6]

Which one did you buy ?

I went for the NASA BM1 - it Looked like it would tell me what I wanted to know/ monitor.

I fitted it earlier this week (with some advice and offer of help from @Richard and Ann but eventually got it done - but haven’t had time to do any kind of testing yet to get an idea of usage etc. which I had previously been trying to do via volts only.

One question for you clever chaps and ladies - my battery is 110amp - should i down grade this is the monitor by a % to reflects its a year old ? i.e it won’t give me 110 amps anymore?

Thanks
Jo

 

[Lenny HB]

One question for you clever chaps and ladies - my battery is 110amp - should i down grade this is the monitor by a % to reflects its a year old ? i.e it won’t give me 110 amps anymore?

Better to be safe than sorry, I'd set it to 100a/h.

 

[Guigsy]

I went all-out and got the Victron BMV 712... I'm a gadget freak and wanted the Bluetooth.

I only fitted it last weekend, so I've not actually used the van yet to find out if it does its job.

Update: We've been touring around Northern Spain for the past week and I've been using the Victron BMV to watch my battery state. I've got a single 100Ah battery. But I'm a fairly low power user (gas fridge, no TV, all LEDs, etc.). And I've also got a large solar panel and it has been sunny... but we've been untethered the whole time and according to the battery monitor I've never taken the battery lower than 86% full. Even when it dropped to 1C overnight and I ran the air heating for several hours (the fan pulls a few amps) and charged the laptop.

My solar charger never seems to produce a lot of power, but it now appears that's because the battery is always close to full. I was considering fitting another battery, but that seems pointless too now.

Given how easy it is to dump and refresh water tanks in Spain, the biggest limitation to going off-grid is how long before my supply of pants lasts before we need a site with a laundry.

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