do these alternator testers work on a battery charger?

[jalikaria24]

hey all im in canada so i have one of these:
https://www.canadiantire.ca/en/pdp/...rger-with-80a-engine-start-0111979p.html

it can also test the alternator so i decided to do it today. i first used my voltmeter/multimeter set to 20vdc directly to the battery and when the truck was on and running it was at 14.2-14.3ish when idling. my vehicle is a 2003 hummer h2 and inside the gauge has a voltage reading too and 14v is the middle and the arrow is always pointing a little less then 14v at all time, even when im driving sometimes it moves a little bit but its never above 14v. so i decided to use my alternator tester function.
the instructions say:
Start the vehicle, rev the engine at 2000
rpm for 30 seconds and turn on the vehicle'sheadlights or other accessories.
4. Set the Display mode button to Alternator %.
5. If the display gives a numeric percentage, the alternator is working properly. The percentage will be proportional to the voltage between 13.2 V and 14.6 V. If the display reads HI or LO, refer to your vehicle's manual or have the electrical system checked.


so when i used it i had my phone camera at record and at idle it was showing 52% ish and then when at 2000 rpm it reached 65%.

so basically does this mean my alternator is fine but just working at 65% of max voltage? i am wondering and asking because i am installing a 55w HID kit very soon and dont want the alternator to give out or something.

attached is a pic of the unit thx

 

[mk378]

It's exactly the same test you did with the voltmeter, only results are presented differently.

Bottom line is that your alternator is working. Also the HID uses about the same power (in some cases less) as the stock bulbs, so the electrical system isn't an issue. (Bad optics and unreliable ballasts are an issue).

 

[GSCJR]

You're alternator is working! IIRC, you recently had to charge your battery? Firstly, I would make sure it's charged correctly, load test it and then confirm you have no parastitic draw. Your battery should not become discharged after only two weeks.

 

[Dave9]

Yes it's just a % instead of a voltage. What it doesn't do is tell you anything about voltage once the new load is added, but 55W is not much so just hook the lights up and then measure idle voltage with everything on that you might use simultaneously, to be sure your engine running voltage stays near 13.8V or better at the battery.

The instructions for it are incorrect and misleading that if you have only 13.2V at the battery, it's okay. That is too low, a sign the alternator is struggling to keep up with the load and the long term solution would be a higher capacity alternator, or run a little smaller alt pulley with the expectation of a corresponding decrease in alternator lifespan.

If your alternator is keeping up with existing headlights and these new aux lights on (or are they replacing the headlights?), the lights won't get noticeably brighter when you rev the engine vs idling.

 

[jalikaria24]

Originally Posted by GSCJR
You're alternator is working! IIRC, you recently had to charge your battery? Firstly, I would make sure it's charged correctly, load test it and then confirm you have no parastitic draw. Your battery should not become discharged after only two weeks.

hmm yeah since we are on the topic of paristatic draw, i dont believe i have any. i usually drive at minimum once every week and it always started uo in the past.
correct me if im wrong but this winter was constantly -40 paired with short 5-10 min drives i believe my battery was discharged for the majority of winter since i never charged it. i then believe it sulfated and now thats why it dies earlier then expected.

i dont want to replace it cuz its only a year old but no warranty on it

 

[kschachn]

All modern vehicles have some sort of parasitic draw on the battery, it just depends on how much and whether it is within spec or not.

 

[Dave9]

It should've been stated, or interpreted, as not having excessive parasitic draw. Any computer controlled engine (era of vehicle) is going to have roughly a couple+ dozen mA, but should be under ~80mA, but may also have a timer circuit that keeps it in a higher draw state until the timer times out or a trigger resets it to start counting again. Common triggers include disconnecting and reconnecting the battery, hood switch, door switch, lights, etc.

We're drifting a bit off the core issue here, and if that 2003 vehicle has an equally old factory alternator, it may be due to fail soon enough regardless of whether the new lights were added, or if aftermarket, may have a shorter lifespan anyway due to that. 55W just isn't that much extra load unless combined with other more power-hungry components like a high power sub amp.