Published: 2022-01-27
MECHANIC: I've got a Renault Trafic here, 2018 I think, and after replacing the alternator there's virtually no charging, there's just over 12 volts, and we'll turn on the lights then suddenly there's charging...
| EXPERT: | Mhm. Does it have a start-stop system? A system with a sensor on the battery clamp? |
| MECHANIC: | Hmm... yes, there is a start-stop system. And a sensor on the clamps too. |
| EXPERT: | OK, so it has what's called energy recuperation and when the battery is full, it doesn't charge. |
| MECHANIC: | So, this is a normal thing? |
| EXPERT: | Yes, if you connect a meter, drive the car and engine brake, it will charge to the maximum, almost 15 volts. |
| MECHANIC: | Oh... |
| EXPERT: | Because it has this micro-hybrid mode. For example at idle it may not charge unless you load it heavily. |
| MECHANIC: | I mean, all you have to do is turn on the lights and it charges. |
| EXPERT: | Yes, because then you load the battery more, and it has to, let me put it this way... it's got to match the current that goes into the battery, a few amps. And if you load the battery more, it will increase the voltage on the alternator, just to ensure this minimum charging current... So, it's ok, it's normal. Don't worry. If the dash lights turn off, and there is communication with the alternator, then everything is fine. |
| MECHANIC: | Well, yes, no lights in dash or anything, I was just surprised because I put on a new alternator and there's just over 12... and there's practically no charging on these daytime running lights. In fact, it's sometimes rising even up to 13. |
| EXPERT: | Yeah, but if you, for example, turn the blower up to max... |
| MECHANIC: | Ahhh... well, but if I turn the lights on it's 14.5. |
| EXPERT: | That's right, because the voltage value... |
| MECHANIC: | So that's... haha :D |
| EXPERT: | ...is regulated to the current. To the current that goes to the battery. |
| MECHANIC: | That sounds right, because it fluctuates, 12.4 sometimes, then after a moment it goes up to 13... |
| EXPERT: | But you probably have an AGM battery or something like that? |
| MECHANIC: | Well, probably yes, because you know... that must be the one. |
| EXPERT: | Well, then that's normal. |
| MECHANIC: | So now you'd have to plug in and see what it actually looks like while driving, but yeah, it could be like that. |
| EXPERT: | If it wants, for example, half an amp to go into the battery, the alternator will be releasing voltage in such a way that the current going into the battery will be exactly as needed, and no more. And it only sustains it, whereas if you engine brake, it will pump it to the max. |
| MECHANIC: | I know, I know, I've done alternator tests with a tester, there's the option... the procedure, where it holds it for 30 seconds at 13 volts, for 13 at 15 volts and it responds fine. |
| EXPERT: | Well, it's all working properly then. The alternator is charging as it should. If it passes the test, it's perfect. And if you drain the battery a little bit, then it will charge all the time. |
| MECHANIC: | Right, well, then... that's it, I guess :) A quick case. |
| EXPERT: | Yeah, and that's why I asked if it had a start-stop, because they do this. |
| MECHANIC: | So, all start-stops have that? |
| EXPERT: | Yes, if you have an AGM battery and this battery sensor on the terminal, then they have it. There's simply no charging because the battery doesn't require it. At the moment. |
| MECHANIC: | Right, well, thanks very much. |
| EXPERT: | No problem, see you later. |
| MECHANIC: | Bye. |