MPPT controller input ripple voltage requirements

Q&A and troubleshooting
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1

We are designing a system utilising a 100 A van alternator charging a stack of Pylontech US5000-1C batteries at a power of 5 kW. We have looked at Balmar charging solution (48 V alternator plus charge controller), which appears to do the job but is ridiculously expensive. The Balmar system does not integrate with our Victron system (Quattro + many Orion dc-dc converters and Orion vehicle battery chargers) and does not meter the charge/voltage or report this to our GX device. We have therefore decided to utilise a Victron MPPT 150/100 in conjunction with a 56 Vdc alternator.

We expect the alternator output to have a ripple voltage of 2.5 Vrms at a frequency of between 2,000 rad/sec and 15,000 rad/sec depending upon the vehicle rpm. We suspect that this level of ripple is unacceptable as the MPPT is merely a buck voltage regulator and will have an unsuitable dynamic response to minimise this ripple requiring us to design a filter between the alternator and MPPT. As the MPPT expects a dc input with no ripple, we suspect its performance may degrade due to any supply line noise.

In addition, it is unclear what level of residual ripple the Pylontech batteries can take without alarming or messing with their BMS.

We are good with designing a filter but are unsure regarding its specification ie what is a maximum ripple voltage that is tolerable at the input to the MPPT. We have designed and modelled a 100 A pi filter, in Matlab Simscape, consisting of a 100 mF capacitor a 200 µH inductor followed by a 10 mF Capacitor. This filter is going to be at least the size of a shoebox, which is undesirable in a vehicle. This brings the ripple down to 1 mVrms. The filter is going to require a soft start mechanism (diode/resistor) due to the large capacitors and is starting to become complicated.

It would be desirable knowing what the maximum tolerable ripple voltage is at the input of the Victron MPPT (between 2,000 rad/sec and 15,000 rad/sec).

In addition, it would be desirable knowing what the minimum dropout voltage of the MPPT is at 100 A ie can it provide 52 V output to bulk charge the batteries with a 56 Vdc input?

In addition, will the algorithm inside the MPPT be ok working with a stiff (big capacitor) 56 Vdc input.

2

If you can source a suitable alternator why not fit it with a Wakespeed WS500 alternator regulator, these can work at 48V nominal and integrate well with Victron equipment and can be controlled by DVCC. The Arco Zeus is similar but I am not familiar with this.

You are unlikely to get answers to your question as this is a community site staffed by volunteers rather than Victron tech support. I doubt that Victron have looked at Vrms on an MPPT as this is a niche use case.

Also, is the stock alternator regulator going to work feeding an MPPT without a battery on the output to dampen the response time, when people have fed a DC to DC charger direct from an alternator they end up with cyclic voltages and currents.

3

Thanks for the suggestions for this we can have a look. There is much blue in the figures so it looks promising regarding Victron. Any suggestions regarding alternator?

Appreciated that the alternator regulator expects to see a battery hence us planning a 100 mF capacitor on the alternator output. Our plan would be soft staring this to 48V using diode and resistor across the MPPT to at least take the voltage to 48V before we crank the vehicle.

With any system which controls regulation by means of the alternator field coils, its not going to do much regarding the ripple voltage. A bit more bedtime reading required here. Suspect a big capacitor :-).

We have raised this with the Victron tech helpline but though that posting would be a good idea too.

4

A Victron MPPT is intended for PV input, full stop. Usage of the device outside of its design is not supported and runs a very real risk of causing damage to itself and/or the other connected components; for your own sake, please do not do this.
Instead, as suggested by @pwfarnell, utilize components that are designed for the intended purpose.

5

No idea on the alternator for 48V.