question

jmz506 avatar image
jmz506 asked

Victron Battery Protect "On resistance"

Hello. I am wondering about the resistance of the Victron battery protect 65, 100, and 220. I am in a situation where the 100A model may be suitable, but the 220A model could make my system more efficient.

Solid state relays have a certain amount of resistance when switched on. An example value is 0.02 ohms. With a 100A load, the power consumed by the relay would be (100^2)*0.02 = 200W. The resistance is also dependant on temperature. I suspect that the 220 model is the same as the 100, just with better heat dissipation.

Battery Protect
1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

airtime avatar image airtime commented ·

Is there an answer from Victron on this? Rds_on seems like a key specification for a switch such as this. I don't want to waste 0.2V or 0.5V on a switch. The on resistance should be specified but I can't find it on the datasheet or in the manual.

0 Likes 0 ·
2 Answers
boekel avatar image
boekel answered ·

It's more like a voltage drop (think 0,2V) and this combined with different A ratings + different thermal dissipation capabilities.

2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

jmz506 avatar image
jmz506 answered ·

Here is a datasheet for Crydom Power Plus DC SSRs: http://www.crydom.com/en/products/catalog/power-plus-dc-series-60-dc-panel-mount.pdf

For the 100A model they list RDS_on = 0.0056 ohms and a maximum voltage drop of 0.56v at the rated 100A current. This means the SSR dispates 56W at the 100A load current. These are common specifications for FETs. Note how the lower current models on the datasheet have a higher RDS_on. Oversizing your relay should make your system more efficient.

I would be happy with knowing the voltage drop of each Victron protect model at their maximum rated load current. This would tell me RDS_on

1 comment
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

kai avatar image kai ♦ commented ·

I would not be surprised if the higher capacity version have more FETs and/or lower RDS_on FETs. Doubling current means 4x ohmic losses, which is a lot to manage just via heatsinking (if the FETs remained the same).

0 Likes 0 ·