CBE CB516 charger working in reverse !!

[BrianK]

Thanks again Derek

 

Understood what you say about the maximum discharge of the batteries, won’t hold you to it :-D

 

a and n caravan services and the late Allan in particulars posts on this forum had a lot to do with my choice of batteries the first place.

 

I think I’m going to try and get a photo of the inside of the charger to ascertain for sure which version I have, although I realise if it’s the later model then the way the switch appears to work doesn’t seem to make any sense.

 

I get what you say about the Elite monitor but I mainly bought it because so many people on forums (including here I believe) suggested it’s performance was brilliant for the money and on par with the likes of the Victron ones. Certainly I will try going through the Chinglish instructions again to try and understand it further.

 

So it seems the best I can hope for is to try and learn my system enough to like you say ‘have a gut feeling’ about when I’m OK and when I might need to go for a drive or tick-over for a while. On the other hand one of the main reasons for the choice of batteries, based on a lot of what Allan repeatedly said, was how much of a waste it can be to purchase the most expensive batteries just for them to fail early, which of course I didn’t do by going with one of the cheapest.

 

Brian

[Derek Uzzell]

BrianK - 2020-10-15 10:10 PM

 

...I get what you say about the Elite monitor but I mainly bought it because so many people on forums (including here I believe) suggested it’s performance was brilliant for the money and on par with the likes of the Victron ones. Certainly I will try going through the Chinglish instructions again to try and understand it further...

 

Brian

 

The NASA BM1 and BM2 battery monitors have certainly been suggested here - but these are more expensive.

 

This 2018 forum thread also mentions a Votronic monitor

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Nasa-Battery-Monitor/48563/

 

(I don’t think the Elite DCM120100C monitor has ever been discussed here before now...)

 

 

 

 

[BrianK]

My mistake Derek it was this Outandaboutlive monitor article I must have been thinking about.

 

https://www.outandaboutlive.co.uk/motorhomes/articles/practical-advice/motorhome-advice-how-to-fit-a-multi-function-battery-monitor

 

Just back tracking a bit. So what is the reason that the monitors (even CBE one it seems) don’t show the voltage anywhere near accurate like a multi meter?

[mikefitz]

Hi Brian,

 

Repeating the points I made in my last comments.

 

The resting fully charged voltage of your batteries will be around 13 volts.

 

The battery monitor you have will not work correctly with lead acid batteries.

 

The additional information you have provided on voltage readings suggests the meter you have is way out of calibration. These low meters have a calibrating setting inside. For an accurate meter you need to pay 10 times the cost of low end meters. It may be the internal battery needs to be replaced. Comparing with a calibrated meter would be useful. I suggest the CBE unit reading around 13 volts is near correct.

 

The recommended 50% maximum discharge limit is a rough guide to prolong battery life. The occasional drop below this value wont make too much difference. The batteries are naturally ageing and have a finite life, regardless of depth of discharge. However each discharge reduces battery life further, the deeper the discharge the shorter the life.

 

The battery monitor shown in the links may give a useful indication of Ah into and out from the battery. However there is no provision for the fact that with a lead acid battery you have to put in more than you get out, due to charge inefficiency. You could need 5% to 20% more, depending on battery type and age. There seems to be no way to set this parameter on the unit.

 

The best cost /performance for battery monitoring is the Victron Smart Shunt,

 

https://www.victronenergy.com/battery-monitors/smart-battery-shunt

 

In conclusion. I think you have no charging problems and the batteries are being fully charged.

( the meter needs to be checked for accuracy)

 

Mike

 

[BrianK]

Mike,

 

I must apologise, I have been on here most days in the last week and have literally just seen this post, and also can’t recall reading your other post (6th October) either, even though I do recall reading all of the others above and below it! I’m not sure if this is possible but could it be there is a glitch in the system here and they weren’t there before? Because quite frankly if not I must be going absolutely potty :-S

 

Presumably I must have been advised about the Redarc chargers output somewhere along the line, it gets a bit involved when you are re-doing all of the electrics like I did but it’s not like me to make the choice without someone with far more knowledge than me to recommend doing something, will re-read my notes and see what I come up with. I do recall Alpha batteries advising that the 14.6 volt bulk charge was fine with these batteries.

 

Is there a simple way to have a calibrated reading done, are garages duty bound to have their's calibrated for instance? And is there a equally simple way to find out the battery temperatures? My assumption would be this is a reading of the cells inside and that no noticeable difference can be felt on the outside of batteries.

 

I see what you say about the care needed to set-up even the more expensive monitors but does the likes of Vitron monitor you linked to, and other top of the range monitors for that matter, suffer from the same issue when measuring? Namely that if I’m often continually starting the engine and moving around the batteries will never have the time to fully rest therefore the monitor can’t possibly provide accurate results? I must say the smart shunt does look impressive

 

Many thanks

Brian

[Derek Uzzell]

BrianK - 2020-10-19 12:58 AM

 

...I’m not sure if this is possible but could it be there is a glitch in the system here and they weren’t there before?

 

Brian

 

In a word - No.

 

I have two multimeters (not expensive ones, but not ultra-cheap crap either) and - for voltages in the 10V to 20V range - the newer meter reads about 0.07V higher than the older one. I’m fairly confident that the newer meter is correct, so that’s the one I use when I decide accuracy matters. But that smallish level of discrepancy really wouldn’t matter in your case because what you are attempting to achieve is unrealistic.

 

You’ve summed up your problem in your sentence

 

I see what you say about the care needed to set-up even the more expensive monitors but does the likes of Vitron monitor you linked to, and other top of the range monitors for that matter, suffer from the same issue when measuring? Namely that if I’m often continually starting the engine and moving around the batteries will never have the time to fully rest therefore the monitor can’t possibly provide accurate results?

 

Obviously, if the equipment you use is itself badly inaccurate or its principles are flawed, whatever readings you get will reflect those shortcomings. But if you operate your camper as you’ve described and want instant snapshots of how much ‘capacity’ remains in your Bosch batteries, it won’t matter how accurate or expensive your equipment is, you’ll never get that infomation.

[spirou]

Victron (and others) count the amps going in/out and from that they do some multiplications based on peukert exponent and charging efficiency etc. to calculate the SOC. So in theory it doesn't matter what you do with the MH, the SOC will reflect the current status at any point in time. In practice, getting those parameters right and SOC accurate is damn hard, not least of which because they change over time and use. I'd say being within 5% of accurate is a decent achievement.

 

So in practice I completely ignore the SOC and look at A, V and Ah displays to guide my actions. If you don't regularly achieve 100% SOC the % will drift more each day. I've seen a case lately where SOC was reportedly just under 60% yet the charger has been through all phases and in float for hours already so obviously at least close to 100, rather than whatever it said. But marketing is such that people completely trust the SOC display rather than think logically. My own worst case was 15% off after 4 weeks on the road.

[BrianK]

Thanks for the input all of you.

 

So it seems to me that in my case I'm probably better learning the system with the tools I already have (subject to checking / calibration like Mike suggested) and through watching what's going on, perhaps even a few tests at home where I leave the fridge on, use the lights and run the engine

 

Spirou, Unbelievably I remember learning about peukert exponent in Physics more than 50 years ago, unfortunately I couldn't get the gist of it then so my 'older' brain definitely couldn't cope now :$

 

Brian

[spirou]

It's quite simple really...useable capacity of a battery goes down as current goes up. The number just tells you by how much.

 

So a battery might have 115Ah at C100, 105Ah at C20 and 85Ah at C5, another will be 115 @ C100, 105@C20, 80@C5, and a third example 115@C100, 110@C20, 90@C5. These are all examples of actual battery specs, just different types from the same company.

As you can see they all behave the same at low currents (of about 1A), but there will be quite a difference at high currents (approaching 20A) with 10Ah difference in capacity between best and worst. So if you calculate the Peukert exponent from these numbers (there are handy online calculators) and the battery monitor can adjust its calculations based on the setting, it will give you a more accurate SOC.

 

The more observant readers probably noticed that the formula can't be completely accurate as this drop in capacity is not linear as evidenced by comparing the first two batteries. But in MH reality you rarely deal with currents higher than 10A so C100-C20 range is more relevant for peukert exponent calculations.