Charger connectivity check
Grade the cellular signal where the charger will stand, and get a setup that holds up. Take readings at that exact spot, at roughly cabinet height, ideally when the site is busy. Readings from the charger or router itself are best. Phone readings work too, and the tool adjusts for the metal cabinet.
How the grade works
Enter RSRP for each carrier, and RSRQ and SINR if you have them. The check subtracts what the charger's cabinet will cost in signal (10 dB by default, and nothing if the reading came from the charger's own modem), then grades each carrier:
- Excellent: -90 dBm or better.
- Good: -90 to -100 dBm.
- Marginal: -100 to -110 dBm.
- Poor: weaker than -110 dBm, or no service.
A noisy signal (SINR below 0) or a congested one (RSRQ below -15) drops a grade. A below-grade location tops out at Marginal. The recommendation then depends on how many carriers grade Good or better, whether a wired connection is possible, and where the charger sits.
Questions people ask
What is a good RSRP for an EV charger?
-90 dBm or better, measured where the charger will stand, after cabinet loss. -100 is workable. Past -110, expect the charger to drop offline now and then, and expect drivers to decide it's broken.
Why not just count the bars on my phone?
Bars are the phone's opinion, and every manufacturer scales them differently. RSRP is a number. Most phones show it in a field test or engineering mode, and free signal apps show it too.
Do I need more than one carrier?
If only one carrier grades Good, one bad day for that carrier takes the site offline. A multi-carrier SIM, or a wired connection with cellular as backup, costs little next to the sessions a dead charger loses. The connectivity guide explains the options.
Does the payment terminal need its own connection?
Many do, and they fail on their own schedule. If the terminal has its own modem, it needs good signal too, and a charger can be online while its terminal is not. Tell the check, and it adds that to the list.