I have a temperature controller with two SPST relay contacts, one each for heating and cooling, and I want to use them to control a Peltier thermoelectric cooler (TEC), plus a fan and pump and potentially a few other widgets.
When either the heating or cooling activates, the auxiliary devices (fan, pump, etc) need to all turn on, with a fixed polarity. However, the TEC needs to have its polarity reversed between heating and cooling, so it can pump the heat in the correct direction.
I have a circuit with the intended behavior, using a series of SPDT relays to handle the 'logic' of reversing the polarity, however there are some issues with it:
I want to be able to run multiple coolers in parallel or perhaps just a single more powerful cooler, but the controller is only rated for 10A, so even two 6A TECs would be too much for this design.
If possible I'd also like to be able to simplify the logic and generally reduce the number of relays I need to use.
I came up with another design that solves some of the issues:
It still draws the current for the auxiliary equipment through the temperature controller's contacts, although in my case that's not an issue since the current is low enough.
In any case though, it feels like there ought to be a simpler way of going about this. How can I simplify or otherwise improve this design?