SSR heating losses

grizzzman

What would be the best DC TO DC SSR amp rating to keep heating losses the lowest?( or any other method for that reason)
 Thanks

mike95490

There are Solid State Relays   SSR
and there are DC-DC converters.     which are you asking about ?

BB.

If you are talking about SSR's... There are a lot of fake/counterfeit versions out there:

https://www.google.com/search?q=counterfeit+ssr

Some of which are built well (and may even be just wrongly/falsely labeled) with smaller/lower current rated devices inside.

-Bill

mcgivor

Solid state relays inherently generate heat and the larger the switched current, the more heat generated. Subsequently using a larger capacity rating for a smaller load will generate less heat, as it will not be running near it's limitations, but will still have losses. Using mechanical DC rated relays would be the best way to eliminate these losses at the expense of slower switching times. As suggested, use name brand SSR's such as Omron if you do decide on using them, beaware that fakes exist, best to purchase from a reputable distributor rather than unknown vendors. All too often, people go broke trying to save money,  on Ebay and the like.

grizzzman

mcgivor said:

Solid state relays inherently generate heat and the larger the switched current, the more heat generated. Subsequently using a larger capacity rating for a smaller load will generate less heat, as it will not be running near it's limitations, but will still have losses. Using mechanical DC rated relays would be the best way to eliminate these losses at the expense of slower switching times. As suggested, use name brand SSR's such as Omron if you do decide on using them, beaware that fakes exist, best to purchase from a reputable distributor rather than unknown vendors. All too often, people go broke trying to save money,  on Ebay and the like.

So is the switching event causing the heat or a steady on or both?
Thanks

mike95490

Both

BB.

For solid state relays--It is probably mostly the level of current flow and the basic resistance of the device (I^2*R heating losses--current squared * resistance = Watts of heat) that is the heating effect (and possibly needing to mount the SSR on a good heat sink/metal surface).

For high frequency switching, there is gate capacitance that lowers efficiency--But that usually does not apply here (very low frequency switching) where switching is occurring seconds to minutes to hours apart--Vs kHz to MHz of switching frequency. I.e.., there is little to no heat when low current is passed through SSRs, but lots of heat at high current (whether DC or AC current).

-Bill

jonr

Most efficient is a latching relay.   With a DC SSR, higher voltages help (ie, less power lost and heat at 48V than 12V for a given wattage).

grizzzman

jonr said:

Most efficient is a latching relay.   With a DC SSR, higher voltages help (ie, less power lost and heat at 48V than 12V for a given wattage).

I considered a latching relay but I worry of burning contacts during the closing event. I am setting up two solar/battery systems that will tie together during high load events (inverter)

mcgivor

grizzzman said:

jonr said:

Most efficient is a latching relay.   With a DC SSR, higher voltages help (ie, less power lost and heat at 48V than 12V for a given wattage).

I considered a latching relay but I worry of burning contacts during the closing event. I am setting up two solar/battery systems that will tie together during high load events (inverter)

Use a DC rated contactor which is rated for the current, such as these  http://www.ametekswitch.com/products/dc-contactors-list
Always use a contactor with  20% or higher rating, than actual current, SSR's have their place, holding high currents for extended periods is not one of them, short durations are fine.

jonr

Agreed.  Use SSRs for short durations, lower currents (common with higher voltages), fast switching, lots of cycles.