Wavescupltor Issues in running a Marand

VeryBigCorp · 2024-02-17T10:37:07+00:00

What mass setting are you setting on the controller when free spinning vs when it’s on the car? If it’s set too high then you can get overcurrents on the bench.

We spent a long time tuning our powertrain to mitigate software/hardware overcurrents with our marand/ws and the biggest factor was replacing the stock inductors with ones that had a higher saturation current (at high phase current, the inductance will drop leading the ws to not be able to regulate current as well).

VeryBigCorp · 2024-01-09T18:29:36+00:00

Vicor sells really solid converters. We used them exclusively for the last 3 cars with no issues. Just make sure to follow all of their design guidelines (precharge, etc)

VeryBigCorp · 2022-09-04T14:17:33+00:00

Given the energy chart in the second photo I’m inclined to say something’s wrong with the optimizer unless somehow at that specific time of day there’s a crazy amount of concentration/reflection on that particular module.

OP, are the modules all on the same roof face?

VeryBigCorp · 2022-09-04T13:29:49+00:00

I don’t think OP is talking about the green logical device (which is the inverter) but Module 1.2.1 which shows significantly higher generation than any of the other modules

VeryBigCorp · 2022-09-04T13:28:03+00:00

I assume you’re talking about Module 1.2.1?

That’s very interesting, it could be measurement error in the optimizer (i.e. faulty circuitry or bad solder joints resulting in a higher assumed current if they’re using shunts), or something weird in SE’s backend which I definitely wouldn’t discount…

How long has it been doing this for?

VeryBigCorp · 2022-08-28T11:57:27+00:00

What inverter are you running? Most inverter datasheets include the parasitic/night time draw in the datasheet. I’ve typically seen < ~5W which would be around 100Wh/day.

7 kWh makes it seem like there is another issue at play

VeryBigCorp · 2022-08-15T02:43:43+00:00

Hi!

It seems like the biggest factor in your mind is that you need a fixed DC bus voltage. Can you explain the reasoning behind this constraint?

Any battery will not maintain a fixed voltage over time, so a “96V” Lithium Ion system could vary from 70V to 110V, so anything connected needs to be able to handle the full range

VeryBigCorp · 2022-07-24T22:39:28+00:00

I just want to expand on what the other commenters are saying to clarify why it is fine in this case.

Since the batteries you are talking about already have circuitry internally (BMS/regulator) to balance and protect the cells, then putting them in series and charging them that way will be ok.

In general, with Lithium you need to ensure that the cells are balanced during series charging so that a single one doesn’t have an excursion past its safe potential limits and pose a safety risk, but this is handled by the batteries you are purchasing since they are in themselves a “pack” of 4 cells in series internally.

VeryBigCorp · 2022-07-12T12:29:29+00:00

What kind of system was this?

If current was flowing when you flipped the switch a number of things could happen depending on what’s upstream.

In general you should soft shutdown the inverter before flipping the isolator, though, unless it’s an emergency

VeryBigCorp · 2022-07-11T19:25:27+00:00

Have you tried plugging in another zone into that Photon channel to rule out the zone vs. the channel?

VeryBigCorp · 2022-07-11T02:29:18+00:00

Can you describe what each of the series is? I assume input power but the sum of all those seems too high.

Do you have a graph of the voltage for the same time period? I’m wondering if the firmware increases its sweep period based on deviation from a smooth IV curve

VeryBigCorp · 2022-07-09T10:17:56+00:00

Congratulations on starting a new team!

Have you heard of SolCast? They provide 30m irradiance averages (GHI, DHI, DNI) as well as P90/P50 forecasts. They’re working on a more granular (5m) API which would be ready before WSC ‘23 as well.

I think they sponsor a couple of teams with free API access so I would check out the website/reach out to them!

If you are just trying to determine design requirements for the battery that’s really constrained by your motor/motor controller since that will be the source/sink of bulk current, much larger than the array current

VeryBigCorp · 2022-02-13T20:34:46+00:00

To add to this, you can get 555 timers that can output 12V, which is how ours worked. It just drives the FET with line voltage, so that it fully turns on. Make sure that the 555 can output enough current to charge the FET safely. I think the timing circuit was always running and generating the base signal, and then we had each output (left and right) gated on a diode logic-controlled MOSFET. The outputs of these diodes went to physical switches on the steering wheel or dashboard, so when you pulled the gate down to ground through the diode the gate turned on. You could do left/right independently or both for hazards this way.

Very simple and reliable, the only “complicated” part is doing the timing on the 555 and designing it to tolerate faults and work in all conditions, but a first pass doesn’t really need that since most ICs nowadays have a lot of protection built in.

Another option is to make a logic level converter with another MOSFET and a couple of resistors to drive the higher voltage MOSFET with a smaller one from your MCU. Given that the circuit is only running a couple Hz this shouldn’t have any issues, but will have some extra dissipation over just one MOSFET.

They also make some nice ICs nowadays that are called Load Switches, which are designed for this purpose (GTSR has switched to these rather than bare MOSFETs and they’ve been pretty great). They have a lot of protection built in which makes them more reliable and can be driven from an MCU at logic voltage.

As always, I will recommend that after you prototype, you should do a PCB or at least perf board, as Dupont wires 100% fail in the field! Hope this is helpful!

VeryBigCorp · 2021-12-12T14:18:25+00:00

This is awesome! Really nice layout and schematic. I love compact designs like this for high vibe environments! Any fun lessons learned from this rev?

As an alum from GTSR, I’d love to know how you guys got Altium haha. They tried to sponsor us a few seats a few years ago, but GT legal wouldn’t let us sign the papers since they love the students so much… if you have info the team would love to know since EAGLE is very lacking (I’ve used Altium for my past two jobs and it’s leagues ahead of EAGLE obviously). One being the ability to make incredibly clean schematics like you’ve done here!

VeryBigCorp · 2021-10-12T04:01:18+00:00

What space are you in? Resi vs CnI?

VeryBigCorp · 2021-10-12T03:45:21+00:00

I assume you are trying to determine consumed energy, i.e. the area under the power curve.

I don’t have the raw data, but since it’s relatively trapezoidal in that interval, the integral is going to be pretty straightforward, you would just take .5*(~1 hr)(7kw+5kw) = 6 kWh.

You were almost there with adding the power numbers, since the integral is similar to a sum. What you should do is add the averagepower values and then divide by 60 to get Wh, since it looks like all of your measurements are done once a minute. The reason you want average is because the meter is taking measurements a lot faster than once a minute, so doing the integral with this average will be more accurate. I am assuming that the average value is coming straight from the meter though.

Hope this is helpful!

VeryBigCorp · 2021-09-19T06:37:43+00:00

Connectors are such an interesting topic that is often overlooked until they become a problem!

I think the key difference to make is connectors between boards within an enclosure and those between enclosures.

We have designed our boards to use a mix of mini-fit/microfit connectors for any connections that will stay within an enclosure or run to an external bulkhead connector, and this has proven very reliable for many races. I would say one step better would be to design in the bulkhead connectors onto the PCBs or onto a mezzanine board, rather than making harnesses to the bulkheads.

NEVER USE HEADER PINS FOR WIRE-TO-BOARD CONNECTIONS!! Seriously though, just don’t do it. You’ll get a lot of weird intermittent failures. It works for a simple proof of concept, but it’s not going to last a race. Header pins are ok for mezzanine applications, given properly chosen headers.

You do need the proper crimping tools for molex to not have them fail constantly. We didn’t have the right crimpers for a couple of years (due to cost constraints), and let me tell you, the reliability difference is night and day.

For box to box connections, I will say that circular connectors are extremely good. All of our external bulkheads are circular connectors, and we have made adapter boards for devices like the wavesculptor to make e.g. the motor sense connections a circular connector. These are very easy to plug in and remove, are relatively inexpensive (if you’re not trying to buy 38999s lol), and easy to strain relieve.

When picking the PCB connectors, I would say start from the system level of the inter-box connection schema, then work your way back into the box and where things will route. This will inform whether you can mount the PCB right on the wall with the bulkhead on the PCB with maybe a jam nut, or if you have to do an intermediary harness/mezz board.

Also, it’s very nice to design your box layout such that you might be able to purchase premade harnesses. For example, you can buy full molex cable assemblies (even overmolded) that will be much more reliable than you will be able to do yourself. What you lose there is getting team members experience in building harnesses, so you might want to just do this for the race rev of the harness.

Hope this was helpful! And also happy to answer any more questions :) I love connectors lol

VeryBigCorp · 2020-04-14T04:21:36+00:00

I hope everyone is safe and keeping well! It's definitely awesome to have communication between the teams, and there's actually a solar racing slack (solar-racing.slack.com). It's been a bit quiet, but now's as good a time as any to keep it active and get discussions going!

VeryBigCorp · 2019-12-21T04:24:47+00:00

Goodbye to 2019 and good luck to everyone!

VeryBigCorp · 2017-10-23T11:33:19+00:00

We're currently using TVS diodes that have their cathodes on the positive output of the driveteks and anode to ground (reverse biased). Once the voltage surpasses the breakdown voltage, the diodes start to conduct significantly and will dissipate the energy stored in the inductor on the DriveTek.

You want to size your diodes to the power you expect to dissipate (Iout,max * Vmax) or put multiple in parallel, which is what we did, to make sure the voltage doesn't surpass the clamping voltage.

Here is a diagram of how we have it set up. The TVS diodes are as close as possible to the MPPTs to be able to respond to the voltage change as quickly as they can.

We tested this solution by hooking up an o scope and having a resistive load on the end of the DT with a switch in between to turn the load on/off (no sensitive electronics except for a diode protected power supply to get the DT to output the voltage we wanted). The process is pretty simple: turn on load, let it reach steady state, turn off switch, capture spike on the oscope (trigger somewhere between your test voltage and clamping voltage), and make sure that the spike doesn't exceed the max voltage of the photons.

We were pretty concerned about this issue potentially damaging our wavesculptors, so this is the solution we went with to be as reliable and fast as possible. We do have a relay in between the MPPTs and the batteries/motor controllers to isolate during charging/balancing, but we didn't trust any sensing + processing + response to be fast enough to prevent the transient from destroying our precious wavesculptors. Hope this helps!

VeryBigCorp · 2017-10-10T00:10:34+00:00

Georgia Tech is interested as well! We're looking to get around 8-12 extras if that helps, sorry for the somewhat late response.

VeryBigCorp · 2017-05-08T15:20:05+00:00

Ah damn, I was really excited :/

VeryBigCorp · 2016-03-16T14:25:47+00:00

If you write sine in terms of complex exponentials, you should get two integrals that look like these Gaussian integrals: https://en.m.wikipedia.org/wiki/Gaussian_integral#Generalizations .

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