Most modern caravans and campers have some kind of monitoring meters installed from new, but for older models, 4x4s and those installing new systems often want to be able to check how their batteries and solar chargers are performing. I often see questions posted on social media platforms like Facebook, asking about the best meter to use. The responses and prices vary wildly with some insisting the units that they may have paid hundreds of dollars for are ‘the best’ and others who suggest more modest units they are happy with. I thought I would relate some ‘real world’ experience that might help people to make an informed decision.
I’ll say right now that what follows is a little ‘geeky’ so if you want to jump straight down to my conclusion and what I recommend – just scroll down to the heading ‘Conclusion’.
Meters that are most useful give an accurate indication of more than just battery voltage as this measurement really only gives an indication of how your battery and charging system is performing. A measurement of the capacity remaining and how much charge current the battery is receiving are important. Battery capacity is also called ‘State of Charge’ (SOC) and I elaborate on the subject in detail in my electrical guide eBook as it is perhaps the most important factor when making decisions about the whole battery setup you will require.
With the advent of Lithium batteries, voltage readings are even less useful – owners of lithium ion cordless drills will be familiar with this when the tool suddenly ‘dies’ usually at the most inconvenient time! This type of battery maintains around the same voltage up until it is almost completely discharged so using this measurement to check the SOC is of little use.
When I set up our van we used for our big lap of Oz I wanted to be able to monitor our two 120Ah AGM batteries to be sure the solar panels were putting in enough power during the day and check how much we were using after sunset. I chose a volt/amp meter from an eBay seller costing under $50 that used a ‘shunt’ on the negative side of the batteries to accurately measure both the current in/out and the voltage. This required some work to install both the shunt and the meter and may be beyond the capabilties of many of my readers.
Important note: There are cheap LCD meters that are sold as suitable for ‘lithium’ batteries. Be careful as the commonly used lithium battery cell type is LeFePo4 (Lithium Iron Phosphate) and most meters that only measure battery voltage to estimate capacity aren’t suitable for this battery type. Check carefully with the supplier before buying this kind of meter.
So, I recently looked for a simpler method that would be much easier to install but also provide an actual capacity readout and be suitable for all battery types including lithium. These types of battery are slowly coming down in price so are a real alternative to the old lead acid battery. This method requires buying two meters (bear with me, they aren’t expensive considering what you end up with!) to enable you to monitor both solar charging and battery condition after the sun has gone down and you are relying on them to power your appliances and lights.
The meter is available from various makers under different brand names including some eBay sellers but I believe it is a good idea to buy from an Australian company to be sure of good after sale support. It is called a ‘Digital Volt/Watt Meter’. These meters are commonly used between solar charging systems and batteries to monitor how much ‘juice’ is delivered to them but another one can be connected between the batteries and the loads (the appliances, lights etc we run from them). Having the Anderson connectors on this model makes it really easy to install and my suggestion is to just make up a small panel for the meters and the connectors can be hidden behind this as once connected, they won’t need to be touched again.
The information the meters provide is great, as well as the ‘live’ display of volts, amps and watts, they show the history of these measurements and also an accurate calculation of the real capacity (shown in Ah or ampere hours which is the rating of our batteries). For example, if we have a 120Ah battery, the display could show say, 20Ah used. Working out what is remaining is simple by deducting this from the available Ah capacity of the battery. In the same way this records accurately and stores how much your solar setup is delivering, so you get a very good idea if it has enough power to meet your needs. Other history measurements available are the lowest voltage levels and peak amps and watts.
I currently have a single meter which I plug in between the solar regulator and the battery, but I plan to get a second unit. When you see the price of the meters and take into account the simplicity of the installation I think you will agree they are definately worth checking out.
Another thing I must mention is that while these meters have a large current measurement capability the cable size provided to the connectors, in my opinion, wouldn’t handle continous current at the high end of the rated capacity. For the vast majority of setups with charging/discharging currents under 50A this isn’t of consequence provided you use reasonably heavy duty cables to connect them. I would suggest placing the meters as close to the battery as possible.
Here’s a link to buy these meters on catch.com.au– they are available from a Melbourne-based company that specialises in offroad components.
This method is a real alternative if you want as much information available without the hassles of installing other types of meters.