Ryobi 48V Mowers
Battery Meter Options
Battery Meter Options
Background
With lead acid batteries, the battery voltage drops noticeably as battery discharges. This makes it relatively accurate to use voltage as an indicator of state of charge. This is how the stock battery meter works. However, with LiFePO4 batteries, the voltage varies a lot less as the battery discharges. This is great for performance, but our stock meter is not going to be accurate for LiFePO4 batteries, so we have to measure the state of charge a different way.
To measure the state of charge accurately for LiFePO4, we use a coulometer. This uses a shunt or hall effect sensor to measure how many Amps are coming in and out of the battery. When we combine that with time, we get Amp-hours (Ah), the same units we use to measure battery capacity. When you install your meter, you configure it for your battery size and the meter will calculate remaining capacity based on how much power has gone in and out. To maintain accuracy, the meter will reset to 100% when it detects maximum charging voltage.
Meter Installation
Most coulometer battery meters use a shunt. This shunt gets installed between the negative battery terminal and the mower so that any power going in or out of the battery has to pass through it. It can be connected to the battery with a cable, or, if compatible, bolted directly to the battery terminal. The meter also needs power from the positive side of the battery, but this is just to power the meter and can be a small gauge wire. With some meters this will go to the shunt and a cable with multiple wires will transfer the power to the meter. In others, you have to run the wire directly to the meter.
The new meter probably won't use the wires from the old meter. They can be repurposed or covered with electrical tape and tucked out of the way.
What about the hour meter?
As you look through the battery meter options, you may notice that none of them include an hour meter like the stock one did. You may still want to keep track of hours for maintenance purposes. In my conversions, I add an hour meter and set the count to match the stock meter. I usually put the hour meter where the USB port was (You can enlarge the hole with a step drill) using the 12V connections from the USB port to power it. You can also cut a hole in the plastic and mount it in the shroud. Here are a few I've used.
A very good meter that includes a job timer.
ZMFJH Hour Meter (Shown in the picture)
Very inexpensive, but a tight fit. You need to remove some metal from the panel bracket too.
To set the time you have to hook it to a battery and let it run for several days.
Basic rectangular meter with a job timer. The display is very small.
Another option is to leave the original meter and mount the new meter in the plastic nearby.
And a third option is to reconnect the old meter under the instrument panel, so it will continue to work, but is out of site. It not convienient to see, but does allow you to continue tracking the hours.
Battery Meter Options
TR16 100A
The TR16 is the most popular battery meter for Ryboi 48V conversions. This is primarily due to it's low cost and high availability.
You can find this meter listed under several brands, but, regardless of the brand, they will be the same except the labels.
Be aware this meter is usually listed with different sized shunts. You will want the 100A shunt. It will handle the range needed and uses 8mm bolts, the same size as most of the LiFePO4 batteries one would use. This way, you can often use the same bolts that came with the meter to attach the shunt directly to the battery.
Sometimes the meter can be listed with different lengths of cable. For most applications, 1 meter is sufficient. If your cable is too long, you can just zip tie the excess out of the way.
This meter comes with everything you need to connect it, except a short piece of wire to connect the shunt to the positive battery cable. For this, you will need 10 - 12 inches of 18 AWG wire with an 8mm (5/16) ring terminal on one end. It can be any color, but red is preferred. If you don't have the tools and supplies to make this, you can ask at a battery store. Usually they are willing to make it for a few dollars.
If you want to put this meter where the stock meter was, you will need to enlarge the hole a bit. This meter requires a 54.5 mm (2-1/8") hole, but the stock meter is only about 49 mm (1-15/16"). The easiest way to do this is with a step drill. It can also be done with a file or die grinder. Some have had success with a grinding stone attached to a drill. Whatever method you use, be sure to wear eye protection and secure the panel to avoid injury. The easiest way to secure the panel is to remove the old meter, push the wire out of the way, and reattach the panel with a few screws.
The TR16 is available under the AiLi brand on Amazon. The prices can vary, but are usually in the $30 - $35 range.
AiLi Battery Monitor (Select "8-80V 0-100A")
If you have more time, it's cheaper to order from AliExpress. It usually takes 1 week to arrive, but can take longer if you live far from an import hub. The prices vary a lot, but are typically in the $20 - $25 range. There are many brands on AliExpress, but the one listed below tends to have the lowest price and I have ordered it multiple times.
Aideepen Battery Monitor (Select "80V 100A")
Coolschmax 100A
This meter is very similar to the TR16 listed above, but with a few differences. The most obvious is the style. It also has an optional low voltage alarm where the display will flash when the alarm voltage is reached. The cable that connects the meter to the shunt is also permanently attached to the meter, making installation slightly less convenient.
Otherwise, the installation and operation are similar to the TR16, including the need to enlarge the mounting hole. See that section for details.
You can find this meter on Amazon or AliExpress, usually for $20 - $30.
Amazon (Select "100A Shunt")
AliExpress (Select "Type 1")
FlyTree FSRC100V
I have not used this meter, but I've included it because some people have been looking for a meter option that doesn't require enlarging the existing hole. This meter is made by the same company that made the original meter, but, unlike the original, this is a coulometer meter. I contacted the seller and they said the shunt is included. This meter doesn't seem as nice as the others, but make be suitable for those who prefer not to enlarge the existing hole.
You can purchase this meter on AliExpress.
