Battery monitors - best way to monitor battery status?

[Lorin]

I am about to install my third battery and split charge system and want a way to monitor the charge status of each of my 3 batteries (two starters and one leisure). However, a top consideration is cost. I know there are some pretty fancy battery monitors out there (notably for marine applications) but they are also expensive. Also most cannot handle 3 batteries.

I've found these (12v digital voltmeters) http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT and was wondering if there is any reason they wouldn't be sufficient for the job. For example, do I need to be able to measure anything other than volts in order to determine the status of a battery? My plan would be to fit one to each of the batteries with a simple switch so that they are not permanently on.

I plan to carry a digital 12v electrical tester on the basis that if a battery monitor indicated that a battery wasnt charging I could check the alternator etc.

It is my intention that the system I install is both simple and idiot proof! Therefore, I figure I ideally need to be able to see if a battery isn't fully charged or is losing charge etc at all times. I also plan to fit a simple alarm to each each of the batteries that sounds or flashes when they drop below a pre-set charge.

Do people think this would be sufficient in terms of keeping an eye on charge/battery status?

 

[Steve Wright]

I am about to install my third battery and split charge system and want a way to monitor the charge status of each of my 3 batteries (two starters and one leisure). However, a top consideration is cost. I know there are some pretty fancy battery monitors out there (notably for marine applications) but they are also expensive. Also most cannot handle 3 batteries.

I've found these (12v digital voltmeters) http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT and was wondering if there is any reason they wouldn't be sufficient for the job. For example, do I need to be able to measure anything other than volts in order to determine the status of a battery? My plan would be to fit one to each of the batteries with a simple switch so that they are not permanently on.

I plan to carry a digital 12v electrical tester on the basis that if a battery monitor indicated that a battery wasnt charging I could check the alternator etc.

It is my intention that the system I install is both simple and idiot proof! Therefore, I figure I ideally need to be able to see if a battery isn't fully charged or is losing charge etc at all times. I also plan to fit a simple alarm to each each of the batteries that sounds or flashes when they drop below a pre-set charge.

Do people think this would be sufficient in terms of keeping an eye on charge/battery status?

Hi Lorin.

Just a bit of advice, instead of getting three units just get one and wire a switch to switch between the three batteries, and with a off position.

The only thing with battery monitoring is, as you say two starting batteries and one leisure, the two starting batteries will be at the same potential IE wired in Parallel, so same voltage no mater if on charge or not, and even the leisure will be again the same potential when on charge, as the other two !

admitting yes it would be nice to see what the voltages are before you throw the starter switch, but other than that I cannot see any need to monitor the voltages.

But the burning question is why do you need to monitor the batteries ?

 

[Lorin]

Hi Steve,

Cheers for the advice. One monitor with a switch between the batteries is undoubtedly a better proposal

The reason I want to monitor the batteries is that it's all prep for a jaunt through Africa. All the batteries will take a bit of a beating through vibration and extremes of temp, so I figured it would be good to monitor them and hopefully spot an issue before it becomes a problem (e.g. a battery begining to lose charge). However, I didn't realise that the two starters would read the same even when not charging. I assume this means there is no way to monitor their individual health without disconnecting them? If that is the case then I need to get some advice on how I monitor them in terms of knowing when I've used the stereo and internal lights enough.

Also, in terms of the leisure battery, there will be a lot of times when it isn't being charged (when we're stopped) but is still running the fridge and other accessories, sometimes for quite a while. I therefore need some way to know (a) when it has reached 100% capacity after a charge cycle that might not have been for very long, and (b) when it is getting low and needs charging again (before I damage it through too greater discharge).

 

[Crispin]

A rotary switch would be simplest for that.
http://www.maplin.co.uk/Module.aspx?Mod ... Code=FF73Q
Make sure you get a Break Before Make switch. If not, you could be connecting the batteries together through the switch. Fire.

 

[Jon Wildsmith]

Will it be an entirely manual system or will you try and automate it e.g. link the aux battery for charging when the engine is running? I don't think Crispin is suggesting you link the batteries with that switch but instead use it to switch a solenoid?

 

[Crispin]

I don't think Crispin is suggesting you link the batteries with that switch but instead use it to switch a solenoid?

Thanks Jon...

Some clarification... I meant switch the tester between batteries to test each one. Not linking them - that would be bad

 

[Lorin]

I might be being really thick here but I thought Crispin was suggesting I use one battery monitor with a rotary switch to click between the batteries. Therefore is only switching the monitor between batteries and wouldn'd be part of the actual charging system.....

 

[Lorin]

In keeping things simple I had thought it would be possible to simply connect the battery monitor to the batteries in some way that is independent of the charging system. That way, if the monitor fails it has no impact on the charging system and vice-versa.

 

[Crispin]

The switch will just switch the monitor between the two batteries. Your leisure and two main ones (Two main ones, in parallel will be a "single battery" and not able to check them individually.)
The monitor and switch have nothing to do with the charging system. Simply switching the monitor between Battery A and Battery B

 

[Jon Wildsmith]

What are you going to use for the charging system then?

 

[24Seven]

Just to add my 2p

With that volt meter...

You're basically going to be monitoring the alternator when the truck is running, which in my small experience is a good idea having seen one fail without bringing the light on, on the dash. The first the guy knew about it when the Landrover failed to start, not a problem when you're with someone who has jump leads, but could a pain if alone even more so when you have camped away from where people normally go in their 2WD cars.

When stopped you will be monitoring in effect 2 circuits of ~12v if you fit a change over switch which could be more trouble than its worth compared to fitting two volt meters????

When a battery is fully charged, it measures something like 12.7v (not on charge) but at something like 12.3v it's half dischanged. Discharging a leisure battery more than 50% can often damage it and shorten it's life.

I don't use my stater battery for anything but starting the truck (within reason anyway) and just use the 110amp/h leisure battery when stopped.

My advice is to keep everything as simple as you can, so as little possible can so wrong, my split charge "system" is 100% mechanical.

Nice guide to leisure batteries Here

 

[Lorin]

Jon, I'm not totally sure. However, my current thinking (which may have a few errors) is:

I am assuming the current factory set-up is perfectly okay at maintaining the two starting batteries and as I will not be drawing power from them for anything when the engine is off other than the interior LED lighting and maybe the stereo I will leave all that alone.

I'm going to use a DC-DC charger such as a CTEK (see http://www.ctekchargers.co.uk/ctek-d250s.php) or similar to maintain the leisure battery so that I can ensure it is charged to capacity.

Other than that I don't exactly know what system or bits I will install but I do know what I want it to do/have:

1) Prioritise starting batteries over the leisure battery so that the leisure battery only starts charging once the starters are fully charged.
2) Be able to be used the leisure battery to start if one of starting batteries dies, although I believe jump leads would sort this...?
3) Include a monitor/alarm for all batteries to tell if okay/how much charge left and warn if low
4) Be relatively easy to fix if breaks (I've read that National Luna are not!)
5) Be water, vibration and dust proof - as much as is reasonably possible
6) Have the leisure battery fully isolated from main batteries so it could drain without affecting the starter batteries

 

[Lorin]

Matt, my thoughts exactly re keeping it simple.

I didn't realise that the monitor would be monitoring the alternator when the truck is running. As you say that is a bonus. Given that I would only need two monitors and not three as I thought, I reckon your right that it may be simpler to just have two monitors, one for the leisure and one for the starters.

Regarding the voltages you mention, I've seen it stated several times as you say that 12.7v is fully charged and 12.3-12.4 is approximately 50%. Does this apply to all the batteries (i.e., both starters and the leisure irrespective of physical size differences?

 

[Steve Wright]

Jon, I'm not totally sure. However, my current thinking (which may have a few errors) is:

I am assuming the current factory set-up is perfectly okay at maintaining the two starting batteries and as I will not be drawing power from them for anything when the engine is off other than the interior LED lighting and maybe the stereo I will leave all that alone.

I'm going to use a DC-DC charger such as a CTEK (see http://www.ctekchargers.co.uk/ctek-d250s.php) or similar to maintain the leisure battery so that I can ensure it is charged to capacity.

Other than that I don't exactly know what system or bits I will install but I do know what I want it to do/have:

1) Prioritise starting batteries over the leisure battery so that the leisure battery only starts charging once the starters are fully charged.
2) Be able to be used the leisure battery to start if one of starting batteries dies, although I believe jump leads would sort this...?
3) Include a monitor/alarm for all batteries to tell if okay/how much charge left and warn if low
4) Be relatively easy to fix if breaks (I've read that National Luna are not!)
5) Be water, vibration and dust proof - as much as is reasonably possible
6) Have the leisure battery fully isolated from main batteries so it could drain without affecting the starter batteries

Where are you going to get 22 volts from ?

 

[Lorin]

Didn't spot that I guess I'm not going to get 22v so that scuppers that. You gotta bear with me a bit here....

My understanding is that if I just charge the leisure battery off the alternator using some sort of split charge system, it will never reach it's full charge capacity. Given how important every extra scrap of available charge could be to me when stopped in the middle of nowhere, I am assuming this would not be the best system for me.

Am I right in thinking that something like a Sterling battery to battery charger (http://www.sterling-power.com/products- ... t-info.htm) would work..? If so, then it is something like that that I would install.

As with all things technical my understanding is poor. What is important to me is that whatever I install is (a) as effective as it can be, and (b) affordable. I have a feeling that the Sterlings are proper money, so I would probably try and find a more affordable alternative if I can't source one second-hand.

 

[Steve Wright]

Didn't spot that I guess I'm not going to get 22v so that scuppers that. You gotta bear with me a bit here....

My understanding is that if I just charge the leisure battery off the alternator using some sort of split charge system, it will never reach it's full charge capacity. Given how important every extra scrap of available charge could be to me when stopped in the middle of nowhere, I am assuming this would not be the best system for me.

Am I right in thinking that something like a Sterling battery to battery charger (http://www.sterling-power.com/products- ... t-info.htm) would work..? If so, then it is something like that that I would install.

As with all things technical my understanding is poor. What is important to me is that whatever I install is (a) as effective as it can be, and (b) affordable. I have a feeling that the Sterlings are proper money, so I would probably try and find a more affordable alternative if I can't source one second-hand.

you have a PM

 

[Jon Wildsmith]

I've got a Stirling DC/DC charger, bought it towards the start of this year, wired it in parallel with a standard split charge system with a change over switch. Seems to do what it says although I haven't done measured back to back testing and it's disconnected at the moment waiting for me to relocate it. The only problem I have with it is it seems to be generating a lot of RF interferance on my HAM & CB radios when it's working hard but I haven't had time to investigate that properly so far. We've been using the fridge in the car as an overflow when we've used the caravan recently and it's been lasting ok on the standard split charge but takes much longer runs to recharge than using the Stirling charger and doesn't last as long.

 

[sae70]

Mmmmm............OK here goes

This is what I've always used

£4.95 from Halfords & just plugged into any 12v power outlet If you could see green all was well no green but red & yellow somethings up only red call a tow truck

Two batteries two monitors as a switch would probally be more than £4.95

Would still use them but now have this

&9.95 local MF & once again the jobs a good'un

 

[Lorin]

Jon, re the Stirling charger, what exactly do they add over a standard split charge? I think I want/need one only because of what I've read elsewhere but I'm struggling to understand what exactly it is they offer over and above a simple split charge system. Given that they are a substantial investment, do you think they're worth it?

The main thing I don't understand is the notion that a standard split charge system doesn't fully charge the leisure battery. Why not, if correct cable and an appropriate relay is used? Surely the alternators full charge going to the leisure battery will ensure it is fully charged.

Also, how does the Stirling charge the battery quicker than the alternator?

Sorry for all the questions, I just had an interesting chat that has resulted in my wondering what a Stirling offers over a simple split charge.

 

[Jon Wildsmith]

The standard split charge set up charges all the batteries together. In a typical senario if your single aux battery is quite discharged but your 2 starter batteries are quite well charged then the aux battery is going to take a long time to charge and won't charge to max capacity because the combined battery looks like it's over 2/3rds full already.

The DC-DC chargers charge only the aux battery and they supply a charge voltage and curve to suit the state of that battery alone so when it's quite discharged that's what it looks like to the electronics and so a higher charge voltage is used which means it charges much faster and much closer to max capacity.

I haven't had mine long enough or done enough back to back testing to give an opinion as to them being worth it or not in real world usage though, sorry.