Voltmeter / Battery Health Monitor

[Ayjay]

I’ve got a CBE Voltmeter connected to the leisure battery which it was fitted when I got the van but TBH was pretty useless with the old AGM battery and is even more so now that I’ve upgraded to Lithium – this one:


I was going to replace it with this:
C-Line Blue LED Battery Voltmeter Display w/ On Off Switch Camper Fits CBE CL3.8 | eBay

Importantly, it turns off as I hate glowing lights in the van at night.

I‘m wondering if anybody on here has fitted one. It's also supposed to give a charge % reading. I’ve looked on-line for further details without success but I’m a bit dubious about the accuracy of any % reading unless you can programme the Ah of the fully charges battery into it as a start point (in my case a 100 Ah Renogy).

I know that I can use the Renogy app for % but it's easier to be able to press a button on the wall.

 

[Dellmassive]

It says 6-30v so a voltage meter is fine.

As for the % who knows?

It must be based on a voltage..... But what? And how? They don't say.... Maybe some fuzzy logic that is self adaptive.

But as you say, the Renogy App or a separate Shunt is the only way to tell SoC.... And even that reading can drift if not charged to 100% regular to keep the BMS in check.

 

[TallPaul_S]

Tbh the Renogy app is going to be your best bet, with LiFePO4 there's 0.5v between 99% and 20%.



Even that voltage display won't really tell you much, especially if there's any load on the system as that will cause the voltage to drop when the state of charge hasn't dropped...

 

[Salty Spuds]

Using a voltmeter to measure the remaining capacity of a lithium battery is pretty pointless due to the way a lithium battery discharges. The only realistic way is to either use the battery BMS if it has the facility, or an external shunt.

 

[Ayjay]

Thanks for the comments guys - I've ordered one for the princely sum of £13 and will see what it's like. At least then I'll have a space filled with something that might be of some use and that looks a bit better than a blanking plate - as indicated above, the thing that's there now was a waste of space even before I went lithium. In the longer term, I might put something more useful in the space but anything involving charging would necessitate upgrading the wiring and fuse as the cable in there at the moment is pretty lightweight (extra PD / QC facilities never go to waste but that's a different post!)

 

[Ayjay]

Again thanks for the input people. It arrived yesterday and I fitted it this morning and it [sort of] all works - Press once for V, twice for % and thrice for off. The readings are slightly out when compared to the Renogy app for the battery with the app reading 13.5V and 99% whereas the new voltmeter reads 13.4V and 91%. All in all I'll keep it as it's infinitely preferable to the thing that it replaced and I suspect something that cheap and simple is never going to be 100% accurate. Annoyingly, the printed 'Voltage' was not quite level in the mounting plate so I filed a small piece out to correct it - it was only when I wired it in and it lit up that I realised the red LED readout actually wasn't quite level with the printing. I can live with that though as it's not permanently on.

 

[roadtripper]

I think a handy rough idea you can see without having to fire an app up is useful - but I'd just go on the voltage the % is likely to be a fantasy.

On the narrowboat we have a Merlin SmartGuage which does a remarkable job of tracking our house battery bank capacity by voltage alone - but that's a £100 bit of kit and needs to know exactly the type of battery to do it's job as well as tracking voltage history over many charge cycles.

 

[Ayjay]

but I'd just go on the voltage the % is likely to be a fantasy

@roadtripper. Agree with that but I'll keep an eye on it when out gets a first extended road trip next month.