Something just learned (1 Viewer)

May 29, 2013
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Maybe others knew this already, but I have just come across it.

Been looking at MPPT controllers and several mentioned having in built temperature sensors, obviously the temperature of the battery can affect the charging rate. I found a controller which had facility for an external temperature sensor so that if, like us, your controller is in a remote place from the batteries you can still get an accurate temperature from the batteries.

In our case the controller is in the small space which also houses the boiler so it will be at an elevated ambient temp. while the batteries are under the passenger seat so they will be at a lower ambient temp. considerably more in winter time.

So I will certainly be buying an MPPT controller with external temp. sensing.
 
Apr 27, 2016
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Maybe others knew this already, but I have just come across it.

Been looking at MPPT controllers and several mentioned having in built temperature sensors, obviously the temperature of the battery can affect the charging rate. I found a controller which had facility for an external temperature sensor so that if, like us, your controller is in a remote place from the batteries you can still get an accurate temperature from the batteries.

In our case the controller is in the small space which also houses the boiler so it will be at an elevated ambient temp. while the batteries are under the passenger seat so they will be at a lower ambient temp. considerably more in winter time.

So I will certainly be buying an MPPT controller with external temp. sensing.
If you buy a Victron SmartSolar MPPT, you can get a BatterySense module that sticks on the battery and transmits the battery temperature and voltage by Bluetooth so that the solar controller can accurately compensate for temperature and voltage drop along the wires. To avoid confusion, the BatterySense is not the same as the SmartShunt which is more expensive, harder to fit and measures amps and amp-hours as well as voltage and temperature.
 
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Jan 27, 2018
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The Votronics range of controllers have the option to add a temperature sensor to bolt onto the battery neg terminal, the B2B come with one in the box. A necessity for Lithium profiles.
 

Hoovie

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The Votronics range of controllers have the option to add a temperature sensor to bolt onto the battery neg terminal, the B2B come with one in the box. A necessity for Lithium profiles.
That is a major simplication.
For Lead Batteries, the charge voltage ideally should vary depending on the battery temperature (the lower the temp, the more the optimum charge voltage can rise) so it can be a handy feature for those.
For LITHIUM, depending on the battery, having a temp sensor could potentially be worse than having no sensor. If you have a charger that turns off if the temp drops below say 3C and you have a Lithium Battery with internal heaters, those heaters are defunct and a waste of money and you lose the ability to get some charging down at low temps.

Lithium Batteries worth fitting in a Motorhome have at the very least a BMS that will disable the Internal charging at low temps so that aspect is taken care of. And if you have that, then while a charger will not be providing charging to the battery when it is cold, it can still provide some power assistance to the habitation circuit which can be useful, which you loose out if you disable the charger itself.
 
Jan 27, 2018
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Hoovie yes a simplification. But in my mind the BMS is the last line of defence not the first. The point about not providing charging to the habitation circuit to me means you are undersized on battery capacity. There are alternative ways. I dont think there are many if any that use my approach of using a BMV712 relay capability to switch an SSR based on SOC to control solar input/output.

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Hoovie

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Hoovie yes a simplification. But in my mind the BMS is the last line of defence not the first. The point about not providing charging to the habitation circuit to me means you are undersized on battery capacity. There are alternative ways. I dont think there are many if any that use my approach of using a BMV712 relay capability to switch an SSR based on SOC to control solar input/output.
Not sure why you want to (or rather NEED to) control a charger based on SOC levels. A good charger should take care of itself. I suppose there are all sorts of weird setups out there.
I do actually use a BMV Relay to switch an SSR based on SOC to control if I allow AC power to go to the Truma Water Heater. (Edit: actually just remembered it is in fact the Cerbo GX relay I use for this - more flexible options available with that).
Also use another BMV Relay to switch an SSR based on freezer temperature to turn the 240V Fridge/Freezer on and off as it gives much more precise control than the basic thermostats they come with. And have another relay, controlled by the room temperature, switching an SSR to turn a couple of sockets on and off so if it gets too cold I have have a room heater come on and/or a heat pad in the water pump cupboard turn on.
Always recommend to people they get the BMVs rather than the Smartshunts so they have the programmable relay available :)
 
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May 29, 2013
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Can I ask people to define technical terms and not use acronyms. Makes it easier to understand.
 

funflair

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Hoovie

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Can I ask people to define technical terms and not use acronyms. Makes it easier to understand.
at what point however do you explain acronyms?
"BMV Relay to switch an SSR based on SOC to control if I allow AC power" could become "Battery Monitor Relay to switch a Solid State Relay based on State of Charge to control if I allow Alternatoring Current Power"? is that really much clearer?
 
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Sandancers
May 29, 2013
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In our technical documents back in the day when I was productive all acronyms had to be listed and defined. That way there was no confusion over what the acronyms meant. But if you want to just keep using acronyms TTUTY (then that's up to you)

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Apr 27, 2016
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at what point however do you explain acronyms?
There is a Motorhome Jargon section that recognises words and acronyms that might need explanation to anyone who hasn't met them before. The jargon word is blue, and has a link to an explanation if you click on it. I think a few additions are required. For some reason it says I have insufficient privileges to post any additions, so maybe Jim could consider adding these:

SOC: State Of Charge. The amount of charge present in a battery, given as either the charge in amp-hours (Ah) or as a percentage of the total charge capacity when full.

Relay: An electrically operated switch. A small current (called the energising or trigger current) causes a large current to flow through the high current terminals. A mechanical relay has a magnetic coil, that pulls the high current contacts together, and a spring pulls them apart when the energising current switches off.

SSR: Solid State Relay. A relay that works by electronic rather than mechanical methods.
 
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Hoovie

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In our technical documents back in the day when I was productive all acronyms had to be listed and defined. That way there was no confusion over what the acronyms meant. But if you want to just keep using acronyms TTUTY (then that's up to you)
that document is now called "the internet" :)

Every industry/interest/subject/etc. has their own acronyms. If they didn't, text and documentation would be so long worded it would be nonsensical. In 'my' old industry - computers and electronics, it is rife and we used to joke about the TLAs that infested it, and the ETLAs (Enhanced TLAs) that then came in.
Basically, if someone has an interest in a subject, they have to both expect to see TLAs used and to find out what they mean themselves (IMO). And with the WWW it is easier than ever to do so by using an SE on their PC.
Of course, YMMV on the subject ;)
 
Jan 27, 2018
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Not sure why you want to (or rather NEED to) control a charger based on SOC levels. A good charger should take care of itself. I suppose there are all sorts of weird setups out there.

Always recommend to people they get the BMVs rather than the Smartshunts so they have the programmable relay available :)
Based on info/advice that LiFePo4 can be treated/used in different ways for max life I use 2 settings call them summer/ winter or Use/resting. Resting with the SOC at x% (pick your value) can also be achieved by issolating the negative terminal. The "Use" value can be whatever you choose 80-100% . If you are fulltime this obviously doesn't apply.
I also reccommend BMV712 rather than smartshunts for precisely same reason.
You obviously use a sophisticated system for monitoring, i use a simple system of an Arduino mega and LCD display taking info from the VE bus and temperature monitors scattered around the place. Why? because i can.
PS I now know i'm doing it all wrong as there are drop in replacements and or a powerbank.;);):giggle::giggle:
 

Hoovie

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Based on info/advice that LiFePo4 can be treated/used in different ways for max life I use 2 settings call them summer/ winter or Use/resting. Resting with the SOC at x% (pick your value) can also be achieved by issolating the negative terminal. The "Use" value can be whatever you choose 80-100% . If you are fulltime this obviously doesn't apply.
I also reccommend BMV712 rather than smartshunts for precisely same reason.
You obviously use a sophisticated system for monitoring, i use a simple system of an Arduino mega and LCD display taking info from the VE bus and temperature monitors scattered around the place. Why? because i can.
PS I now know i'm doing it all wrong as there are drop in replacements and or a powerbank.;);):giggle::giggle:
I think you sound as convinced as me regarding 'drop in replacements' :)

As far as treating Lithium the 'right way' by limiting the level of charge and level of discharge, I don't doubt that there is something in that.
But on the flip side, by doing that to extend the life of the Lithium battery, you (this is the generic 'you', not you personally BTW) are limiting its usefulness and amount you can get from it per charge cycle. I have my doubts personally whether this is something worth bothering about as the total amount of Ahs drawn from the battery will not be much greater, they will just be drawn over a longer period of time; plus whilst you may be extending the service life of the LiFePO4 cells in the battery, will the cheap electronics in the BMS last the duration anyway? and for the typical Lithium battery and the typical Lithium Battery user, a broken BMS means a defunct battery (one of the advantages of treating Lead better is you WILL almost certainly get a reward from doing so. The verdict on if doing the same with Lithium is more than theoretic mathematics rather than proven at this stage).
Other reasons (IMO) not to sweat the Lithium Charge/Discharge numbers is there is likely to be a better and cheaper battery available by the time the Lithium will have hit its normal 100%-0% use charge cycle service life and there is a fair chance the batteries will be swapped out anyway even if they have been 'treated better'.
Any finally .... will you get to see the extended life of the batteries anyway? the quoted service life of a Lithium battery, quoted in charge cycles, is so high even with unsympathetic use, that the average motorhomer will end their service life before the battery does!

So while I am certainly not advocating mistreating batteries, I really am not convinced about the importance to manage their charge and discharge patterns as closely as some folk advocate.
My own pair of Lithium Batteries are rated at 6000 cycles on a 50% DoD. They are often down to 20% and even if that halved the life down to 3000 cycles, that still means if I discharged them 3 times every week they would still be good for 20 years!
Do I really need to bother to limit the discharge to 50% to get 40 years from them? I would prefer to get 160Ah each time for 20 years than 100Ah so to have them last 20 years longer than I would ever need them to.
 
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May 29, 2013
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that document is now called "the internet" :)

Every industry/interest/subject/etc. has their own acronyms. If they didn't, text and documentation would be so long worded it would be nonsensical. In 'my' old industry - computers and electronics, it is rife and we used to joke about the TLAs that infested it, and the ETLAs (Enhanced TLAs) that then came in.
Basically, if someone has an interest in a subject, they have to both expect to see TLAs used and to find out what they mean themselves (IMO). And with the WWW it is easier than ever to do so by using an SE on their PC.
Of course, YMMV on the subject ;)
Strangely enough I worked in electronics / software / instrumentation. But because all the work involved situations which could be classed as hazardous no one could use undefined acronyms. SSTUYA.

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Jan 27, 2018
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As far as treating Lithium the 'right way' by limiting the level of charge and level of discharge, I don't doubt that there is something in that.

So while I am certainly not advocating mistreating batteries, I really am not convinced about the importance to manage their charge and discharge patterns as closely as some folk advocate.

Do I really need to bother to limit the discharge to 50% to get 40 years from them? I would prefer to get 160Ah each time for 20 years than 100Ah so to have them last 20 years longer than I would ever need them to.
My approach has changed since installation in that during "rest" i treat it with upmost respect. But durring "use" i look at my weekly trend and am not worried about full charge or the odd daliance with 10%. My first two years of use with 100Ah convinces me that my FLA's (Pb acid, Wet Lead) were allready on way out on pickup ( a year on fourcourt). Please note i did not give any number you should follow and my thoughts are closer to yours than you think. My usage is likely to increase with the purchase of e-bikes but at least we have a 12V charger. So may have to at least look at levels as oppossed to telling those that do to just get the washing machine out and do it. She was so used to asking have we got the power to " ". Now the answer is "has it been raining for a fortnight" if not Yes.
 

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