PlanB wrote: Replacement caps & fets? Do you guys have a service manual or something? So far there is a dead PIPs & Rpi here, casualties of the learning curve. The Pi is a throwaway but we'd be interested in PIPs resurrection.
A fellow who lives near both Kurt and I, had an earlier version of the PIP-4048 for about a year. He had the model where the MPPT was not built in, but was a separate product. He contacted Kurt (and Kurt invited me) to show and tell about the PIP blowups he'd had. The first two times, it was fixed under warranty. He had AGM (lead-acid) cells. The MPPT was not properly controlling the voltage near end-of-charge and was making excursions to 63 V, which is the rating of the PIP's DC bus caps. These caps also had only a short rated life at their maximum ratings -- 2000 hours which is about 3 months. And that's about how long they lasted. Towards the end of this life the caps' impedance would have risen to the point where they could no longer control the inductive voltage spikes from the PWM switching and some MOSFET(s) would blow. The MOSFETs only had a 75 V rating. Hardly any headroom to speak of. It's common to use double the maximum DC bus voltage.
So I researched suitable replacements with higher voltage ratings. It wasn't easy, particularly when limited to 18 mm diameter caps by the PCB layout. But here's what I settled on:
Caps: United Chemi-con EKZN800ELL 182MM40S, 1800uF 80V radial
Digikey part 565-4129-ND
MOSFETs: International Rectifier IRFB4310ZPBF, N-ch 100V 120 A TO-220AB
Digikey part: IRFB4310ZPBF-ND
The caps (4 of) have much lower capacitance than the original Jamicon WLR332M1JL44RT9 caps, which would be bad if it were not for the fact that they have nearly the same 100 kHz impedance.
Capacitance, voltage, ripple, impedance, endurance (at 100 kHz and 105°C)
Original 3300 uF, 63 V, 4.57 A, 15 mR, 2,000 h
Replacement 1800 uF, 80 V, 3.86 A, 17 mR, 10,000 h
Hopefully the 5 times longer endurance more than makes up for the 15% lower ripple current rating.
I note that the "Z" in the replacement MOSFET part number is important. There is a part without the "Z" that is not up to the job. The IRFB4310Z has almost identical specs to the original IRFB3307 except for being 100V instead of 75V. I replaced all 16 MOSFETs. Replaced the silicone thermal washers too, on the 8 that had them, and used a thin smear of heatsink grease on the ones that didn't need insulation from the heatsink. The originals were put on dry, which is bad.
Despite replacing the caps and MOSFETs I have not yet succeeded in fully repairing the PIP. I found some resistors open circuit in the MOSFET driver circuitry as well, and replaced them, but the blowup must have propagated further back up the driver chain.
As Kurt says, I gave his PIP a pre-emptive upgrade. For complicated reasons, I did not end up doing this to the PIP in Monolith #1, which has been running as an off-grid solar power system for 2 months now (PV array 3.5 kW 72 V nominal, Battery LiFePO4 180 Ah 48 V nominal).
Kris, it would be great to know how yours blew up, so we might avoid this, if it isn't too embarrassing.
[Edit: Added Digikey links. Aligned cap specs. Changed "caps (8 of)" to "caps (4 of)".]
One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).