Help with voltage dividers

[nsled]

Are voltage dividers to measure the voltage of HV capacitors a thing? or is it done by other means?

I've tried to model it, seems ok until I realised there is only 5nA of current left to measure after 1:1000 division. Will voltmeters measure this low current?

I've used 5MOhm on R1 to keep it to a reasonable 5W.

[klugesmith]

You set up a circuit simulator and picked a voltmeter from library.
A voltmeter with 1-gigaohm impedance.  What does your simulator show about voltage and power at the ammeter?

What you need is a realistic voltmeter, with input impedance substantially higher than 5 kiloohms.
Or put a realistic milliammeter in place of the 5k ohm resistor.

Consider changing the 5Meg resistor to 4.995Meg if you want a 1000:1 division instead of 1001:1.

It is common to measure HV using a multi-megohm resistor in series with analog or digital panel milliammeter.
Often the meter is shunted with a permanently-connected resistor or nonlinear device, to limit the voltage in case panel meter is accidentally disconnected or goes open circuit.

[nsled]

Okay thankyou, I guess I know nothing of input impedance.

The ammeter shouldn't really be there and can be ignored it shows zero zero.

I'm pulling parts out of a shed from over a decade ago and you've made me realised what the string of 5 100Mohm 10W resistors was for. It had me baffled but no doubt it was to wire into an analogue meter.

[MRMILSTAR]

The easiest way is to use a microammeter and a high voltage resistor. For example, I use a 25 microamp meter in series with a 1G ohm high voltage resistor to measure 0 to 25 KV. The ammeter scale reads directly in kilovolts.

[nsled]

I think I'm understanding, the reason for using an ammeter instead of voltmeter is because it has very low resistance.

And this physically is the same thing https://www.aliexpress.com/item/1005002267936039.html?spm=a2g0o.cart.0.0.28d438daueGLXf&mp=1 I checked user reviews and it shows in a pic to come with 500Mohm resistor.

[MRMILSTAR]

Correct. Those voltmeters are actually microammeters with a voltage scale reading in kilovolts. As the ad says, you must use a matching high voltage series resistor.