Electricity in your Motor Home for Dummies

[merl]

A rule of thumb.= A rough and useful principle or method, based on experience rather than precisely accurate measures.
it is in that context that r4dent and many others ( E.g 12volt Planet) use 50% and imho is entirely appropriate in the context it was used. If you don’t find it useful then that’s your call.

Your text in bold highlights one of my points, the 50% guidance/rule (which has now morphed into the law) ISN'T based on experience is it? How many people who are spouting this rule ACTUALLY have the experience of how discharging to say 60% has affected their battery life massively over and above what they got from a 40% discharge? I'd argue virtually NO ONE can and further any 'experience' as such could easily be affected by other sources like temperature and sitting at a partially charged state so the 'firm experience' becomes anecdotal experience.
This rule isn't based on experience, it's based on a snowball effect of people parroting useless advice over and over again until it becomes fact.
Yep, I know that there's lots of references to the 50% rule all over the place including established business that repeat the rule parrot fashion without any significant reason or backup. Funnily enough I've just watched 2 of the QI elves on the BBC only this morning commenting on just how much 'common knowledge ' is actually incorrect. They included an example of the high that you get from heavy exercise, typically running isn't from Endorphins (as is widely accepted) but from a chemical similar to the stuff in cannabis. Spinach isn't massively high in Iron either.
When I see the FACTS about how exactly a battery's life is affected by how much you discharge it by looking at a cycles Vs depth of discharge plot I see 50% as a point on a sliding scale and cant see for the life of my this stupid rule has caught traction.
I've a notion that it actually comes from battery manufacturers data when, back in the day, they wanted to give an indication of how many cycles a customer could expect from a battery, as we know (from the discharge plots) that this depends on how deep you discharge it so the makers had to decide on how much to discharge for a test? Well they chose 1/2 way...50% and this has lead to a widely held assumption that 50% is OK and anything deeper is bad. TOTAL GUFF!
As already pointed out this guide is aimed at newbies but armed with poor info a newbie could easily sit in the dark at night because they were scared of taking their battery below 50%. David/Wildbus agrees with me and has previously said that he's done the maths and a deeper discharge point can actually give better bang for your buck, now I've not checked his maths but from the plots is easy to see that the damage gets worse the deeper you discharge, the line isn't straight but there's no significant 'heel' or drop off point either so the 50% rule makes no sense.
So, here's a challenge, you say you feel the rule is "entirely appropriate" but can you explain why (other than 12 volt planet and his dog says so) it's appropriate? Take a look at a life Vs depth of cycle plot and explain why 50% is an appropriate rule and 60% or 40% or ANY other percentage for that matter isn't just as appropriate?

 

[r4dent]

Ok, I'm sorry if you feel offended, I did include a 'sorry' in my post. Now, I'm going to say more, non of which should be taken as a personal poke because it's not meant that way, it's just me pointing out what I feel to be the wrong information that gets repeated time after time (hence the here we go again remark)
My post was a reaction to your post above NOT what you've written in your guide which I haven't read but I'm sure is very good.

50% maximum discharge makes little sense, would 60% be so much worse? Would 40% be so much better? The fact is that damage gets worse the deeper you discharge, Period. But you also get more capacity so it's a trade off.
I've used the smoking analogy before which I'll repeat.
No fags is best
Chain smoking is worst.
A rule of thumb saying "30 a day is ok" is the battery equivalent of the 50% rule.
One fag ain't going to kill you and 1 deep discharge won't kill your battery either but I've actually seen a 'knowledgeable' poster on another forum saying that it would, so deeply has this 50% nonsense been regurgitated over and over.
Sorry but as you see I don't agree when you say that 50% is a valid rule of thumb and, if you have suggested the same in your article then I think you should consider changing that part for something else possibly with a chart plotting cycles Vs depth of discharge (they can be easily found for virtually all leisure batteries) which says a thousand words.
Anyone who can understand the nominal capacity calculation which you included shouldn't have a problem grasping the graph and I guess actually factual and helpful to not only the newbie but for most/many not so newbies too.
You've taken the time and effort to write your article and I praise you for that but don't keep regurgitating the same old crap mate, you're better than that.

You obviously feel strongly about this matter and regard it as very important and potentially damaging.

I do not wish to mislead anybody by regurgitating the same old crap
I can no longer edit the original post because it is too old.
Hopefully this statement will help minimise any future damage damage

Page 1 of the document contains the following
"How long will my battery(s) last before they are flat?
Hours = [ Nominal Capacity (Ah) *6 ] / Watts]"

This formula is based of the old rule of thumb that a battery will only provide 50% of its nominal capacity.
This is an over simplification and discharging a battery to 50% may damage the battery.

I can no longer edit the original post because it is too old.
I suggest you report my original post to Admin and ask them to add this statement or your preferred statement to my original post.
.

 

[merl]

You obviously feel strongly about this matter and regard it as very important and potentially damaging.

I do not wish to mislead anybody by regurgitating the same old crap
I can no longer edit the original post because it is too old.
Hopefully this statement will help minimise any future damage damage

Page 1 of the document contains the following
"How long will my battery(s) last before they are flat?
Hours = [ Nominal Capacity (Ah) *6 ] / Watts]"

This formula is based of the old rule of thumb that a battery will only provide 50% of its nominal capacity.
This is an over simplification and discharging a battery to 50% may damage the battery.

I can no longer edit the original post because it is too old.
I suggest you report my original post to Admin and ask them to add this statement or your preferred statement to my original post.
.

Respect due! I hope you don't feel bullied and you've now you've actually joined the 'dark side'

 

[marchie]

Speaking as someone who was told not to take Physics at O Level, because 'you'll be wasting the Examiner's time'; and as one who got a Grade 9 O Level Fail in Chemistry, because there wasn't a Grade 10 level, Guides that say something akin to 'To preserve your battery, don't take it below 50%, especially as it ages', are very useful. It leaves a wee bit of scope for the 'Well, tonight, we ain't got much choice if we want light, but keep usage to a minimum' option, with sufficient caution to show that you should recharge asap, and investigate quickly if the battery isn't recharging/holding charge, especially for occasions when neither David Wildebus nor Jeff Mossy are on the same Rally or Site ... . Apps and downloadable Battery Voltage [Lead Acid & Lithium] Charts give reassurance/guidance until either David or Jeff appear ...

Rule of Thumb is to reach one's own limitations before reaching those of the Battery for peace of mind ...

Steve

 

[merl]

Speaking as someone who was told not to take Physics at O Level, because 'you'll be wasting the Examiner's time'; and as one who got a Grade 9 O Level Fail in Chemistry, because there wasn't a Grade 10 level, Guides that say something akin to 'To preserve your battery, don't take it below 50%, especially as it ages', are very useful. It leaves a wee bit of scope for the 'Well, tonight, we ain't got much choice if we want light, but keep usage to a minimum' option, with sufficient caution to show that you should recharge asap, and investigate quickly if the battery isn't recharging/holding charge, especially for occasions when neither David Wildebus nor Jeff Mossy are on the same Rally or Site ... . Apps and downloadable Battery Voltage [Lead Acid & Lithium] Charts give reassurance/guidance until either David or Jeff appear ...

Rule of Thumb is to reach one's own limitations before reaching those of the Battery for peace of mind ...

Steve

I see what you're trying to get at but why 50% ?

 

[marchie]

I see what you're trying to get at but why 50% ?

You're asking the wrong person, Merl! I have a Lithium Leisure Battery and did overdo it when I tried the then new 1200w Inverter in May of this year, so I know now roughly where the safe lower usage limit is [just before the Control Panel, the Victron App and the KS Energy App sound alarms, shut down systems and start the flashing lights display ...]. I have downloaded a Lithium Charging Chart as a reference point to enable me to get a rough idea of how long the battery recharging will take, and what economies of usage I need to take in the meantime

I am a belt/braces and sock suspenders character, who underwent Captain Mainwaring era training in the Bank, so I'm always likely to feel more comfortable with a decent safety margin, quite apart from the fact that I am technically inept [or, more correctly, inept in matters technical', 'cos I ain't 'technically inept', I'm actually inept, so I lack the skills to put matters right if I overstep the safety margin ...

David Wildebus fitted an Ablemail AMT12-2 Battery Trickle Feed to keep the Vehicle Battery charged, and wired it to be permanently fed by the Lithium, unless I press the 'On/Off' switch to suspend operations. That's technical enough for me!

Steve