My house battery starts to feed into the grid when the printer or the heating bed is on. so seems that the inverter does not like.
Probably the regulation of the inverter is slower than the bed.
Does anyone know the “frequency” with which the bed is regulated?
I don’t know if this is healthy for the inverter in the long run or if you can just ignore it. it’s annoying that electricity is “sold”, but because of this I don’t want to invest in HW again which prevents this.
Yes, there is some sort of regulation. I think it’s more PTC than PWM. I measured the power draw decreasing as the bed heated up. Since you are in Europe, I’ll comment that the bed draws about 900W on 240V, compared to 300 or so on 120V. This is more likely the reason for the battery issue.
The Bambu technicians responded quickly and provided me with the necessary information:
The full CE certificate and the relevant information that the bed operates at 1Hz.
I can put together the situation so far that the inverter also works with ~1 Hz but not synchronously with the printer. the “current” is always there when the printer does not need it. so it goes into the power grid.
The question is whether this is unhealthy for the inverter or just a cosmetic problem. (apart from the fact that energy is wasted).
my neighbor is an electronics dude and said an EMI line filter could help. Theoretically, but the capacitor must be large enough?
edit:
ah… I owned some DIY 3d printers and they also had a 230V heating bed. There was no problem.
The switching times of the PID control were more sluggish.
I’m not sure I completely understand what you are saying but it sounds to me like this is due to the response time of your battery inverter and the manner in which it supplements your supply. It sounds like the inverter is switching its output on and off in an attempt to track a load which is also being switched on and off, but out of sync. The response speed of the inverter or it’s sense sampling is not responsive/fast enough. When they are out of sync, the inverter can’t track. I don’t think a UPS will help any (this is for when the supply is cut or for smoothing higher frequency supply transients), neither would an EM filter (which is for higher frequency interference issues). If the inverter has some kind of time response setting or load threshold setting then you could try changing that. I would not have thought it was unhealthy for the inverter as the design should be able to cope with any kind of changing load, it’s just that it is feeding the supply when it doesn’t need to because of the slow response time of its sensing control system. I could be completely misunderstanding the issue, in which case I apologise.
(BTW, carrying on from @holmes4 comment, IF the instantaneous power of the bed is dependent on the supply voltage and IF your printer is compatible with the voltage (check its ratings label or the manufacturer), you could try reducing the instantaneous load by using a 240V to 110V/120V isolating transformer to your printer (like the type tradesmen use for corded tools), but you would need to check first that your model is compatible with a 110V/120V supply and that the isolating transformer has sufficient power rating. Whether it is compatible will depend on the design and whether Bambu have designed in the ability for the same unit to work on a large range of mains voltages or whether they ship different designs for different mains voltages. However, I can’t see that doing this would be a brilliant fix, really, due to the cost of buying and the power losses of the transformer. It’s possible it might work.)
I started reading at the top and was about to say very similar. I have a house battery and through a good part of the year am totally self-sufficient but still see small demands from the grid. I think you nailed it - it can’t instantaneously track the demand. Especially stuff with big startup currents the demand can come and go faster than batteries can track the load. I have my system minimize demand from the grid and still see draw and have watched it in real time as a compressor kicks in.
About it being a problem for the battery and electronics, I would bet it’s not an issue just because it’s pretty common behavior that it has to deal with. I would say anything that can’t roll with it during repeated surge situations is defective in design because PWM and other off/on with surges control of loads is very common.
It sounds like OP may not be on net metering and still has to pay for any electricity that enters the home. Unfortunately, there probably isn’t a way to help that. I’m on net metering so anything comes in from the grid is coming from the net surplus I have banked with my utility and is free. When/if I use that up, any net power from the grid will cost me but that tally comes at the end of the billing period.
Just as an aside, that’s interesting about the way your ‘net surplus’ works. I assume you are in the States. So does your electricity provider allow you a kind of buffer that you can fill and empty? A bit like having your own house battery in the cloud? Effectively, you get paid the same amount for the electricity you produce as the electricity you use so long as it is within this ‘buffer’ amount? How enlightened. Is that how it works? Over what period of time is the net metering period? Do you have to pay more per energy unit compared to a non-net metered tariff?
It used to be like this in the UK when people first got home PV back in the 2000s for anyone with an old spinning disk electricity meter that went backwards when instantaneously net generating. They soon put a stop to that. I bet there are still a handful of people with the old meters and PV, though. Now typically you get paid something like a quarter of the price when generating (exporting) compared to when pulling from the grid. It’s why house batteries and EV batteries are popular, to help locally store the excess.
It’s pretty much like that. For the duration we’re in the house and basically under contract with the electric utility, there is an energy bank associated with our account. We can put energy in and take it out however we want but if we ever draw more energy out than was put in during a year, we get billed for the net out at the going rate. But it is pretty much a cloud-based battery except the sources are gas, coal, wind, and solar here when I’m drawing from the grid.
Pricing is same as other residential customers. We even get the benefit of discounts and settlements that regular customers get. We have some kind of settlement over something at a coal power generating station that reduced my monthly $9 grid connect fee down to $1. It’s actually a very good deal but the utility also sees a lot of extra power into the grid from residential solar during the day - right when they need the most power. So they benefit too. They don’t have to build more power plants.
The down side comes when we sell the house. Our contract ends and if there’s still energy banked, they buy it from us at the producer rate which is very low. It’s not economically attractive for residential system owners to oversize to generate excess. We are restricted to how much power we can put back on the grid to not overload the lighter weight transformers and wiring the last mile, anyway. The limit they set is 10kW. A system can’t put more than that on the grid.
Very interesting, thank you. The domestic grid transfer limit in the UK is just 3.7kW per phase by default, but you can apply for higher. Most houses are single phase connected, but I believe you can pay to get 3-phase.
On my side it seems to be fixed after inserting a filter between socket and power cord.
My issue was the other way around, when my inverter is loading the battery with pv power, it draws the 800W for the printer from grid althouth the inverter should have taken the power from pv.
From my point of view it some kind of EMI problem.
Just seeing this now - all the Bambu printers support 120-240V input - only the power cord varies by country. The bed is driven by line voltage, unlike the rest of the printer, so its power draw is some 4X on 240V what it is on 120V.
Effectively, you get paid the same amount for the electricity you produce as the electricity you use so long as it is within this ‘buffer’ amount? How enlightened. Is that how it works? Over what period of time is the net metering period? Do you have to pay more per energy unit compared to a non-net metered tariff?