[rcheshire (Rowland)]

With the internal TEC set at 1.2 volts, which seems to be its optimum and the external TEC set sequentially from 1 - 7 volts, cooling is less effective > 4 volts. Not published here, but from 8 - 11 volts cooling is ~0.5C/V, after which there is no significant benefit.

Without the external TEC fitted (that is, 0v) the internal TEC max delta is ~8C, which is consistent with the trend shown below. The only way to reduce the delta further (which would have been nice last night with cold temps and dew point near freezing), is to reduce the internal TEC voltage in 0.2 - 0.3v increments and see what gives.

The 8 - 12v data was acquired using a good quality SMPS. The reason for not including it here is that the difference between 7 and 11 volts is just 3C, using a 6amp 40 x 40 TEC. At 8 amps the delta is around 20C at 12volts - marginal at best.

EDIT: Not impressed with the latest batch of dc dc convertors. Not robust at all. 8 volts ~3 amps, rated to 6amps, burnt out. Suggest if buying these, limit input to 7 volts or provide lots of cooling.