Insulation Tester - Page 1
Forum section: electronics / beginners

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 20, 2023, 08:02:24 pm
content: I just bought a cheapy insulation tester, an Aneng MH12. I was checking it out and connected it to some small carbon or metal film resistors in order to see if resistances are in the ball park. I set the tester to50 VDC an put the probes across a 6,8 M ohm resistor and got a reading of 10.3 M ohm. Then I measured a 22 M ohm resistor and got 32,5 M ohm.What am I missing here?

author: BillyO
author_rank: Super Contributor
timestamp: July 20, 2023, 08:18:08 pm
content: Quote from: BILLPOD on July 20, 2023, 08:02:24 pmA good insulation tester.These cheapies are ball-park devices at best and are not really intended to test resistors.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 21, 2023, 07:37:30 pm
content: Thank you BillyO, for your response. I would hope my 'cheapy' UM12tester would be 'in-the-ballpark', but the readings seem to be in adifferentballpark. Would you, or someone else with a GOOD insulation tester check what readings they get on some M ohm resistors to see if there are some other factors at play that would cause such wild results?Thanks.

author: BillyO
author_rank: Super Contributor
timestamp: July 21, 2023, 08:06:32 pm
content: I don't have an insulation tester otherwise I would.Specs say +/- 5% (of range) and +/- 10 counts. So yours does seem to be off a little.

author: Gyro
author_rank: Super Contributor
timestamp: July 21, 2023, 08:18:38 pm
content: The high voltage source on cheap insulation testers can sag under the load of 'low' value resistors. This causes a lower than expected current through the resistor and correspondingly higher resistance readout. Itmightread better at 100M+

author: 555
author_rank: Newbie
timestamp: July 21, 2023, 08:22:24 pm
content: I have measured some resistors with my Fluke 1507:10M: 10,5M @50V - 10,62M @1000V47M: 47,2M @50V - 47,33M @1000V

author: srb1954
author_rank: Super Contributor
timestamp: July 21, 2023, 10:35:31 pm
content: Quote from: BILLPOD on July 20, 2023, 08:02:24 pmConnect a DMM to the insulation tester output and check that it is putting out the correct test voltage. It should be within 20% of the specified level.Check on other test voltages as well but first check that your DMM is rated for the maximum test voltage. If the test voltage significantly deviates from the specified figure that might affect the accuracy of the resistance readings. In that case I would suggest that you have a a faulty unit and should return it.The resistance reading when the DMM is connected should be either 10Mor 11Mdepending on the model of your DMM. This reading should not vary significantly across the differently test voltages as the input resistors in a DMM are generally more stable than the average resistor at higher voltages.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: July 22, 2023, 01:11:58 pm
content: A big thank you to all who responded. I 'think' I've discovered the problem......I put NimH batteries in it. Even though they were fully charged, (all just over 1.3 VDC), it was not close enough to the 12 VDCthe meter requires. I don't have any 1.5 VDC primary alkaline cellsbecause of the leakage thing, so I ordered some lithium primary cells and will re-test when they arrive, and report back here. Thanks again

author: xavier60
author_rank: Super Contributor
timestamp: October 25, 2023, 09:51:37 am
content: A TEKTROM TTE511 Insulation Tester I bought a month ago runs fine on NiMh cells.I just did a quick resistance accuracy test by connecting it to my Fluke 87V on DCV range.The TTE511 displayed 10MΩ +/-1% on each of its voltage settings.As well as the insulation resistance, it also displays the actual test voltage. Insulation testers try to maintain a constant test voltage up to some current limit.This is the only meter I could find in the $100 price range that also has a 200Ω continuity range.My particular meter had a fault causing poor accuracy on the continuity range, a faulty BJT in its 1mA current source.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: October 25, 2023, 06:55:20 pm
content: OOPS.......I forgot about this matter, but here is the ending of my escapade.......I filled my Aneng MH12 insulation tester with primary lithium batteries, (it takes 8 of them), and it works like a champ. Even my 40Mresistors read real close to spot on. Now to test all my insulation.

author: BeBuLamar
author_rank: Super Contributor
timestamp: October 25, 2023, 07:34:04 pm
content: When I was still working I had a Fluke 1577 and it has the resistance function and insulation test function separately. I never compare the reading between the 2.

author: Terry Bites
author_rank: Super Contributor
timestamp: October 26, 2023, 04:02:18 pm
content: Insulation testers do just that. They check you're in range. They are not intended as high voltage ohm meters.You can get those of course- expect to haemorrhage (sorry yanks) cash.

author: Gyro
author_rank: Super Contributor
timestamp: October 26, 2023, 06:07:05 pm
content: It depends which one you have. My second hand Kewtech achieves 1.5% + 5 digits on the 20M and 200M ranges. Accuracy does drop off to 10% + 3 on the 2G range though. That's with 250V/500V/1kV source maintained to 1mA, ie, down to 1M on the 2G range. You can pick them up for <£30 in the UK if you bide your time. I don't know what sparks in the US use but don't neglect professional used stuff.

author: nightfire
author_rank: Frequent Contributor
timestamp: October 27, 2023, 07:05:05 pm
content: Do the test again with 500VDC- some el cheapos have issues when used below 250VDC.(Also applies to the more expensive appliance testers from the big brands, that they need to be used with higher voltages to produce correct results.)Also a good idea as mentioned is to measure the voltage put out with a DMM that can handle that- and within a DMM we know we have some precision resistors.