Inverter Overloading

[Nordicsoul56]

Hi Jon,
First, thank you for the kind words and welcome to Grand Design's Technical Forum. There's quite a few (retired) engineers here (not me!) so you'll fit right in.

I'm reading your post early in the morning so my brain is still a little foggy--what does "SPS" reference?

EDIT: Now that I'm awake (and I was working on a schematic) it accorded to me that "SPS" is AMSolar's Smart Phase Selector. The relays do not, IMO, alleviate the need for the SPS. Without the SPS only one leg of the camper's 120v circuits will have access to power from the Victron inverter.

Howard

P.S. Continuing this thread is fine.

Good morning Howard,

Actually when using a dog bone adapter whether it be 50 to 30 amp or 50 to 15 amp, line 1 & 2 are connected together at the source, and when you are on 50 amp service and lose power the SSR does as you intended. I think I'm still on target here? The draw back I see is not being able to have the Victron 3000 add load from the batteries since line 1 & 2 are tied together at the 120VAC source.
I'll have to noodle this further.
My intent was saving +$400 of the SPS but then again Crydom's aren't exactly cheap either... so it may be a moot point.

Best regards,

Jon

[howson]

Good morning Howard,

Actually when using a dog bone adapter whether it be 50 to 30 amp or 50 to 15 amp, line 1 & 2 are connected together at the source, and when you are on 50 amp service and lose power the SSR does as you intended. I think I'm still on target here? The draw back I see is not being able to have the Victron 3000 add load from the batteries since line 1 & 2 are tied together at the 120VAC source.
I'll have to noodle this further.
My intent was saving +$400 of the SPS but then again Crydom's aren't exactly cheap either... so it may be a moot point.

Best regards,

Jon

Jon,
The software used on this forum can be wonky sometimes, so the reason your post was "unapproved" was likely you edited it too many times too quickly. The admins have not been able to figure out a fix, so the moderators (me being one of them) have to approve the post for it to be seen. No big deal, just wanted you to know why that happened to your post.

I may not be understanding...so forgive in advance that we may need to reword what's being said a few times before I comprehend.

Let me start with the dogbone. I agree the SPS is acting like a dogbone in that when providing 120V from the inverter it provides power to both legs by combining them. However, power is limited from the inverter (max 25A) just like power is limited from a 30A pedestal connection.

The benefit of the SPS is when connected to a 50A pedestal there is 50A available to separate legs simultaneously--a total of 100A. None of this is being inverted, it's all from shore power. If shore power shuts off, the SPS switches (like an automatic transfer switch should!) but now, even though both legs are connected to the inverter, there is only 25A from the Victron.

The reason for the SSRs is when the loss of shore power is inadvertent. Water heater is on, both air conditioners are humming away, refrigerator is on...and power fails. The SPS kicks over as designed, but now the power demand is outstripping the inverter's capability. The SSRs act as "load shedding devices" and turn off unnecessary items reducing the demand.

I hope that makes sense.

Howard

[Nordicsoul56]

Jon,
The software used on this forum can be wonky sometimes, so the reason your post was "unapproved" was likely you edited it too many times too quickly. The admins have not been able to figure out a fix, so the moderators (me being one of them) have to approve the post for it to be seen. No big deal, just wanted you to know why that happened to your post.

I may not be understanding...so forgive in advance that we may need to reword what's being said a few times before I comprehend.

Let me start with the dogbone. I agree the SPS is acting like a dogbone in that when providing 120V from the inverter it provides power to both legs by combining them. However, power is limited from the inverter (max 25A) just like power is limited from a 30A pedestal connection.

The benefit of the SPS is when connected to a 50A pedestal there is 50A available to separate legs simultaneously--a total of 100A. None of this is being inverted, it's all from shore power. If shore power shuts off, the SPS switches (like an automatic transfer switch should!) but now, even though both legs are connected to the inverter, there is only 25A from the Victron.

The reason for the SSRs is when the loss of shore power is inadvertent. Water heater is on, both air conditioners are humming away, refrigerator is on...and power fails. The SPS kicks over as designed, but now the power demand is outstripping the inverter's capability. The SSRs act as "load shedding devices" and turn off unnecessary items reducing the demand.

I hope that makes sense.

Howard

Thanks for the heads up on the software.

Okay so the more I think about it I'm betting you can't tie the Victron 3000 input and output together (which happens when using a dogbone and no SPS).

I imagine we'll be camping at less than 50 amp locations so the 30amp or 15 amp is a more likely scenario. I was hoping the crydoms might be a less expensive solution.

It was a nice thought while it lasted but it's back to using the SPS :p

Best regards,

Jon

[DkYork]

Hi Howard,

I may have missed it, but did you have the bedroom AC still running like you wanted when you lost shore power? I need a similar solution because we have animals and in hot climates. I'm still building out my entire system and very glad I found your post. I have 3 ACs in my unit, so it will definitely overload. I'm thinking my manual workaround would be to turn off any heavy appliances before we leave, but this is cooler. Lol.

Thanks,

DK

[howson]

Hi Howard,

I may have missed it, but did you have the bedroom AC still running like you wanted when you lost shore power? I need a similar solution because we have animals and in hot climates. I'm still building out my entire system and very glad I found your post. I have 3 ACs in my unit, so it will definitely overload. I'm thinking my manual workaround would be to turn off any heavy appliances before we leave, but this is cooler. Lol.

Thanks,

DK

Yes. I have two small dogs that are crated in the bedroom when we leave the camper. If shore power drops off the bedroom a/c stays on.

I don't think I've mentioned it before, but I added microair easy starts to my air conditioners. They are a worthy upgrade to at least the air conditioner that may run off the inverter.

[steve&renee]

Hi Howard,

I'm still in planning mode for switching from a 4 ea. 6V battery bank to a 4 ea. 12 V bank, so I've been studying a lot of your (much appreciated) diagrams.

In the one above, I just now noticed that it appears you ran 4/0 ground wire between the inverter and the battery bank, but retained the OEM 6 gauge ground to the trailer frame. Is that correct?

Can you explain why its OK to make the frame wire so much smaller? I would have thought that the connection to the trailer frame should be heavy gauge, too.

Thanks.

-Steve

[howson]

Hi Howard,

I'm still in planning mode for switching from a 4 ea. 6V battery bank to a 4 ea. 12 V bank, so I've been studying a lot of your (much appreciated) diagrams.

In the one above, I just now noticed that it appears you ran 4/0 ground wire between the inverter and the battery bank, but retained the OEM 6 gauge ground to the trailer frame. Is that correct?

Can you explain why its OK to make the frame wire so much smaller? I would have thought that the connection to the trailer frame should be heavy gauge, too.

Thanks.

-Steve

The only power that runs through that original 6ga ground wire are circuits related to the OEM trailer wiring. The largest single fuse in that circuit (on the Power Distribution Panel) is 30A (slide fuse).



All of the heavy 12vDC amperage loads to/from the battery/inverter are through the 4/0 and 2/0 wires and are protected by the 400A fuse.

The reason the 6ga wire is connected to the shunt is so the BMV-712 "counts" the amperage being consumed from the batteries by the trailer's OEM circuitry (lights, etc). Every path back to the batteries must go through the BMV's shunt.

Garret does a much better job of explaining:

Let me know if it still doesn't make sense and I'll try explaining differently.

Howard

[JohnD]

Howard,
Great idea on the L2 disconnect on loss of shore power. I have the same concerns that you expressed in your description concerning having my dog unattended in the RV. I plan to incorporate this in my design as well, so thanks for the info.

I looked into the Smart Transfer Switch, and they are backordered, so I'll probably have to do a workaround with a manual switch for the time being. I am curious about the neutral wiring though, as the diagram gives the impression of the neutral being switched in addition to L1 & L2. The Multiplus appears to separate the AC input neutral and the AC output neutral, but I wonder if this is electrically isolated. I'm guessing the Inverter Neutral output (Shore In Neutral) is always passed to the output Neutral of the STS, so I wonder why it is not just a bus bar for the neutral on the STS. The Manual Transfer Switch diagrams I have found always show the Inverter Neutral Output fed to Electrical Panel, with only the L1,L2 switched.

[howson]

Howard,
I am curious about the neutral wiring though, as the diagram gives the impression of the neutral being switched in addition to L1 & L2. The Multiplus appears to separate the AC input neutral and the AC output neutral, but I wonder if this is electrically isolated. I'm guessing the Inverter Neutral output (Shore In Neutral) is always passed to the output Neutral of the STS, so I wonder why it is not just a bus bar for the neutral on the STS. The Manual Transfer Switch diagrams I have found always show the Inverter Neutral Output fed to Electrical Panel, with only the L1,L2 switched.

I'm not knowledgeable enough to answer a question at the depth, John. OffToHavasu, TucsonJim or Jkwilson...help.

[Guest]

Load shedding as Rob stated is commonly used in the auto industry these days where its very effective in not leaving folks stranded. But this is controlled through a sophisticated software program that involves CAN messaging to force off devices. Wondering if a dual EMS might be used for each leg with some wiring mods in a simplified application? It looks like the Inverter is trying to fire but the surge is just too much to handle the load. There are also some large Capacitors out there that may help on the 12V side. We also use those in some applications with the auto stop start feature to keep systems alive while cranking.

Jim

[OffToHavasu]

Howard,
Great idea on the L2 disconnect on loss of shore power. I have the same concerns that you expressed in your description concerning having my dog unattended in the RV. I plan to incorporate this in my design as well, so thanks for the info.

I looked into the Smart Transfer Switch, and they are backordered, so I'll probably have to do a workaround with a manual switch for the time being. I am curious about the neutral wiring though, as the diagram gives the impression of the neutral being switched in addition to L1 & L2. The Multiplus appears to separate the AC input neutral and the AC output neutral, but I wonder if this is electrically isolated. I'm guessing the Inverter Neutral output (Shore In Neutral) is always passed to the output Neutral of the STS, so I wonder why it is not just a bus bar for the neutral on the STS. The Manual Transfer Switch diagrams I have found always show the Inverter Neutral Output fed to Electrical Panel, with only the L1,L2 switched.

Just for clarity, are you asking about the differences of say the transfer switch (SATS or standard) vs. a Passthrough Inverter transfer?

[JohnD]

Just for clarity, are you asking about the differences of say the transfer switch (SATS or standard) vs. a Passthrough Inverter transfer?

I'm new to all these devices, and not familiar with a Passthrough Inverter Transfer. I'm also not familiar with other types of transfer switches other than a manual one. My thought was to install a manual one until I could get an automatic one. Any input on other options is welcome. I was just curious why the SATS gives the appearance of "transferring" or "switching" neutrals (from Gen or Shore to Output) according to Harold's diagram. Perhaps I'm just over thinking it.

[OffToHavasu]

Generator transfer switches (Auto) transfer both legs and the neutral. The grounds are bonded. Inverters the transfer is built in (passthrough) so I'd imagine there's a disconnect of the neutrals in there, but I'm not 100% sure on that.

[Jkwilson]

Howard,
Great idea on the L2 disconnect on loss of shore power. I have the same concerns that you expressed in your description concerning having my dog unattended in the RV. I plan to incorporate this in my design as well, so thanks for the info.

I looked into the Smart Transfer Switch, and they are backordered, so I'll probably have to do a workaround with a manual switch for the time being. I am curious about the neutral wiring though, as the diagram gives the impression of the neutral being switched in addition to L1 & L2. The Multiplus appears to separate the AC input neutral and the AC output neutral, but I wonder if this is electrically isolated. I'm guessing the Inverter Neutral output (Shore In Neutral) is always passed to the output Neutral of the STS, so I wonder why it is not just a bus bar for the neutral on the STS. The Manual Transfer Switch diagrams I have found always show the Inverter Neutral Output fed to Electrical Panel, with only the L1,L2 switched.

When using an onboard AC power source such as a generator or inverter, the power source neutral has to be bonded to ground. When using shore power, the ground and neutral can’t be connected within the RV.

This bonding switching is generally handled by the ATS wiring. If the neutrals weren’t switched, the neutral would always be connected to ground inside the RV. Shore power has the neutral and ground bonded in the panel. Adding another bonding point results in the ground wire carrying part of the neutral current. Not good.

If the output of the inverter has its ground and neutral bonded internally, if you connect shore power neutral to inverter neutral, there will be problems.

[JohnD]

I hope I am not derailing this thread. I would like to understand how the SATS works. (I will probably have to contact AMSolar directly). Since I can't get an SATS for some time due to back order, I was going to do so manually, and I've found a wiring diagram on the internet referencing a Battle Born install. I would like/expect the manual connection to operate the same as the automatic - kind of a sanity check. I intend to position and wire the manual configuration such that it is very easy to replace with the automatic SATS when it becomes available. I will try to clarify my question. The below diagram shows a manual transfer switch before the breaker panel, and the upper left hand corner shows the wiring detail.


In the above diagram with the manual switch, in all scenarios (50A, 30A,15A, No Shore Power), the electric panel neutral is supplied by the Multiplus AC Output Neutral, and all AC current flows through this neutral. In all single phase situations (30A,15A, No Shore Power - manually switched to position 2), the inverter supplies both legs of the panel. In the 50A shore scenario (manually switched to position 1), L2 of the panel is supplied directly by Shore L2, and L1 is supplied by the AC Output of the Multiplus, but again, both legs are returned via the Multiplus AC Output Neutral.


I understand that the SATS configuration automatically powers the two legs of the electric panel based on single/dual phase as described in the manual switch. I'm wondering if/what logic it might apply to the neutrals. Does it always supply the "Shore In" Neutral to the breaker panel as shown in the wiring diagram for the manual switch? If not, what logic is being applied? I was also curious as to whether the Multiplus electrically isolated the AC Output Neutral from the AC Input Neutral.