MPPT Controller but no Battery Management Panel

[Guest]

I've just had 2 x 100w of solar fitted with a MPPT controller. There was an option to have a battery management panel (BMP) fitted too but when I said that I had an Alde boiler, the fitter said that I couldn't have the panel because of the way the Alde is wired in. I'm afraid I didn't understand the reason behind this...it was explained but I just didn't get it.

 

The display on the controller is this:-

 

 

 

It shows me, amongst other things, the voltage of the batteries...13.7 in the photo. This gives me peace of mind because before the solar was fitted I had no way of knowing the state of charge of the batteries. Now, I feel I don't have to start the engine every day even when I want to stay in the same place.

 

My question is, what extra information would a BMP give me that the display on the controller doesn't and as I can't apparently have a BMP, can I rely on the display on the controller.

[b0atman]

Do not understand why you cannot have a battery management panel ?

One bit of advice check voltage at both ends of cable from mppt to Battery I get volt drop on mine so am increasing cable size why waste whats free from the sun .

[MyLady]

Do remember that if there is any input current the voltage shown is the charging voltage, NOT the voltage the batteries can produce. If you wait till there's no input current for a significant time - 10 to 30 minutes - that will show the true battery voltage (and ideally, the batteries should be under some load.)

 

While the sun shines, our MPPT controller (Tracer 30A) shows anything from 13V to 14V, if the engine - and so, the alternator - is running, but after dark we only hope for 12.7V - and sometimes get as little as 12.3V. In the latter case, we know not to draw much current until the sun shines again, or we're cruising again, preferably both!

 

Hope that helps. We don't have a SOC meter, but I think we're learning how to interpret volt-meter readings. Time, or truly expert opinion, will prove us right or wrong...

 

Roger

Edited August 1, 2014 by MyLady

[Guest]

Do remember that if there is any input current the voltage shown is the charging voltage, NOT the voltage the batteries can produce. If you wait till there's no input current for a significant time - 10 to 30 minutes - that will show the true battery voltage (and ideally, the batteries should be under some load.)

 

While the sun shines, our MPPT controller (Tracer 30A) shows anything from 13V to 14V, if the engine - and so, the alternator - is running, but after dark we only hope for 12.7V - and sometimes get as little as 12.3V. In the latter case, we know not to draw much current until the sun shines again, or we're cruising again, preferably both!

 

Hope that helps. We don't have a SOC meter, but I think we're learning how to interpret volt-meter readings. Time, or truly expert opinion, will prove us right or wrong...

 

Roger

 

Thanks for this. I now have a better understanding that the mppt controller shows me what the panels are producing and an indication of what I'm using but only after 10 - 30 minutes of no input current. I guess a battery management panel would show me what I'm using.

[musicman]

I don't understand the comment made to you about your Alde heater.

I have an MPPT controller and run a Smartguage alongside it.

I have all the information I need.

[phill]

 

 

.

Just as a matter of interest, which controller is this?

[bottle]

 

Thanks for this. I now have a better understanding that the mppt controller shows me what the panels are producing and an indication of what I'm using but only after 10 - 30 minutes of no input current. I guess a battery management panel would show me what I'm using.

 

Nearly there.

 

That display only tells you what the panels and the MPPT are doing and will tell you the battery voltage when the sun don't shine ie, it's dark outside.

 

Now, battery voltage can be an indication of battery SOC (State Of Charge) but as said only after the batteries have rested for a few hours or a load has been applied to dissipate the 'surface charge' and then all loads removed, the reading (voltage ) taken.

 

An example of where battery voltage tells you nothing about your batteries, slightly sweeping statement but in this case for illustration and to keep it simple.

 

Batteries fully charged and have a voltage of 12.6v, a heavy load is applied, the voltage will drop (depending on load), the batteries are still fully charged but discharging, the voltage could be as low as 12v indicating flat batteries but of course they are not, turn off the load and the voltage will recover and if allowed to rest will give an indication of SOC as long as no load is 'ON'

 

The simplest way to know your batteries SOC is the Smartgauge but that costs in the region if £160, a cheaper way is volt meter and amp meter, then you would need to learn how to interpret them.

 

ps. Try to never let your batteries go below 12.2v, 50% SOC (at rest, no load). This is the guidance given as a balance between battery life and costs.

[Beaker]

Just as a matter of interest, which controller is this?

 

This is same as ours, as supplied by Tim Davis (Onboard Solar).

 

I don't know the brand, the model is eMPPT30.

[Grace and Favour]

Just as a matter of interest, which controller is this?

Chinasolarregulator

[MyLady]

Nearly there.

 

That display only tells you what the panels and the MPPT are doing and will tell you the battery voltage when the sun don't shine ie, it's dark outside.

 

Now, battery voltage can be an indication of battery SOC (State Of Charge) but as said only after the batteries have rested for a few hours or a load has been applied to dissipate the 'surface charge' and then all loads removed, the reading (voltage ) taken.

 

An example of where battery voltage tells you nothing about your batteries, slightly sweeping statement but in this case for illustration and to keep it simple.

 

Batteries fully charged and have a voltage of 12.6v, a heavy load is applied, the voltage will drop (depending on load), the batteries are still fully charged but discharging, the voltage could be as low as 12v indicating flat batteries but of course they are not, turn off the load and the voltage will recover and if allowed to rest will give an indication of SOC as long as no load is 'ON'

 

The simplest way to know your batteries SOC is the Smartgauge but that costs in the region if £160, a cheaper way is volt meter and amp meter, then you would need to learn how to interpret them.

 

ps. Try to never let your batteries go below 12.2v, 50% SOC (at rest, no load). This is the guidance given as a balance between battery life and costs.

 

Just what I'd have said, if I knew enough! The point is that if current is flowing (or has done so recently), the voltage shown on your controller has more to do with that current than with the SOC of the batteries - and it doesn't matter whether the current is in or out, that's still true. If current is flowing out of the batteries, the voltage measured is lower than the SOC would give and if the current is flowing in, the voltage will be more than the SOC would give. And even when the current is nil, the batteries need time to recover from any 'surface effects' to read accurately. The trouble is that time with no solar input and no load is inconvenient - wasting sunshine or being without the fridge etc. In time you'll get the experience to guess, reasonably reliably, what's going on even when you don't cover the panels, or switch EVERYTHING off. If that guess isn't accurate enough for you, then a SmartGuage will give you a much better estimate ... but it costs (but then new batteries cost even more if you knacker them).

 

Our demands are very low (12V Lec fridge, water pumps when we turn taps, or the shower, on (or want to flush the loo), phone and laptop charging, plus a few LED lights and, through tunnels, our headlight - minimal mains devices, just a walkie-talkie charger). At this time of year, a simple guess is that our 330W - soon to be 495W - of solar will cope and last winter we did cope (but used the fore-deck instead of the fridge), cruising for a few hours most days, so a decent guess about what's happening 'today' is, we think, good enough for us. If you have a TV, washing machine, any power tools, etc. you'll be more vulnerable, so a SmartGuage would probably be worth its price; I'm thinking a DC clamp meter is probably worth buying so that I can measure, rather than making an informed guess, at demands - all meters cost something, even the cheapo ones off eBay, so if you don't yet have any, a SG (instead of another voltmeter and ammeter) looks cheaper than the raw cost. Of course, if you want to identify some problem, you may need them all.

 

You pays your money and takes your choice...

 

Ignorance is bliss until you really need to know! The people on here are great at telling you about things in theory, or in principle, but sometimes you actually have to measure things for yourself (or pay someone 20 quid an hour to measure them for you (and to travel to where your boat is) - if/when you can find someone - then 60-80 quid for meters, 160 quid for a SG, or even both, can sound cheap - especially if they tell you that you need to spend ~400 quid on new batteries if you got it wrong!)

 

Roger

Edited August 2, 2014 by MyLady

[Guest]

Thank you Roger and Keith for your very helpful advice.

 

P.S. Tim Davis of Onboard Solar supplied and fitted the system too.

[MyLady]

Thank you Roger and Keith for your very helpful advice.

 

P.S. Tim Davis of Onboard Solar supplied and fitted the system too.

 

Hi Shirley,

 

I don't know much, but I am learning! If you can benefit from that, great!

 

All the best,

 

Roger