Charging a higher voltage bank than a PV panel or string? (and a bonus question)

treed678

I should know the answer to this, but I've never done or seen it. E.g., your bank is 36V and you have a 24V panel, but the CC has a 36V bank setting. Will the CC bump the voltage to charge the bank? If not...

Part 2....

What happens if you use a boost converter between a bank and CC? Let's say the converter states or can be adjusted to 36V level charging - e.g., 42V, etc. Can it be assumed that the converter uses a fixed multiplier, and is therefor safe (sort of, ha!) to charge a bank with a different (higher or lower) voltage than the CC is designed for? Seems risky.

Cariboocoot

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

treed678 wrote: »

I should know the answer to this, but I've never done or seen it. E.g., your bank is 36V and you have a 24V panel, but the CC has a 36V bank setting. Will the CC bump the voltage to charge the bank? If not...

Part 2....

What happens if you use a boost converter between a bank and CC? Let's say the converter states or can be adjusted to 36V level charging - e.g., 42V, etc. Can it be assumed that the converter uses a fixed multiplier, and is therefor safe (sort of, ha!) to charge a bank with a different (higher or lower) voltage than the CC is designed for? Seems risky.

The answers are: no, no, and yes it can be done.

The typical charge controller, even MPPT type, will not boost output Voltage.
A few charge controllers such as some made by Genasun will.
Just using a buck booster between the charge controller and battery will be a no-go because the connection needs to be a direct two-way so that the controller can read battery Voltage accordingly. Placing the electronics of a booster in between will interfere with this: they are meant to take a fixed Voltage on one side and convert it to a fixed Voltage on the other. They do not perform the way a transformer would on AC.
You could in theory put a buck booster on the panel(s) and output higher Voltage to the controller's input to begin with. Whether the booster would take the input characteristics of PV (current source, not Voltage source) is another matter.

treed678

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

Figures. It didn't make sense many would boost voltage, but now I know some can!

I mentioned 36V specifically because I haven't seen much selection for solar controllers that support this voltage. Or have I just not looked hard enough? My interest is in how to address uncommon bank voltages (Pb only - no lithium, etc which I believe are less forgiving/more dangerous).

Cariboocoot

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

treed678 wrote: »

Figures. It didn't make sense many would boost voltage, but now I know some can!

I mentioned 36V specifically because I haven't seen much selection for solar controllers that support this voltage. Or have I just not looked hard enough? My interest is in how to address uncommon bank voltages (Pb only - no lithium, etc which I believe are less forgiving/more dangerous).

The higher-end (i.e. expensive) MPPT controllers can usually be programmed for 36 Volts and/or slight variations (+/- 2 Volts say) from standard Voltages. It's one of those things that needs to be checked very carefully before buying a controller as sometimes companies will drop support for 36V just because so few people use it.

treed678

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

Thank you. By the way, I'm curious how your Honda is setup with the OB. I sold the system in my sig, but I plan to build again. I got a lot of questions about 240V. I only used/needed 120. The option is either master/slave w/ 2 inverters or the OB transformer if only 1 inverter, right? Is yours automatic? I plan to use a generator in my next build. The eu2000 a good choice it seems.

Cariboocoot

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

treed678 wrote: »

Thank you. By the way, I'm curious how your Honda is setup with the OB. I sold the system in my sig, but I plan to build again. I got a lot of questions about 240V. I only used/needed 120. The option is either master/slave w/ 2 inverters or the OB transformer if only 1 inverter, right? Is yours automatic? I plan to use a generator in my next build. The eu2000 a good choice it seems.

The EU2000i is 120 VAC. The VFX3524 is 120 VAC. No problem connecting the two. It is all manual: the Honda is manual start only and I just don't need automatic gen start.

I have an autotransformer to power my septic pump which is the only 240 VAC load. It is turned on manually when needed & when power is available.

treed678

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

Ah, ok. I think I remember it being 120 VAC now. Autostart isn't necessary for me either, and what I do next time will most likely be 120 VAC again, so I'll keep it as a consideration. Still curious how 240 VAC could be setup with 1 or 2 OB's, and a different generator could be automatically started (wiring, safety, etc), but I'm just being lazy now. Always so much to learn... This, wind, and hydro could make good winter reading.

Cariboocoot

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

Well if you're really curious Outback has a ton of wiring diagrams showing the various methods of stacking inverters for parallel current applications and serial Voltage applications, including 3 phase output and utilizing autotransformers for balancing and with 240 VAC gen inputs for single charging or double charging. This is a key feature of the FX inverters: their flexibility. It makes nice reading for long Winter nights.

westbranch

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

'Coot, a bit of a technical question/sidebar discussion on this topic please.

WE (the royal we) are in the midst of having the electrician doing the wiring at the new place and now want to wire in a 220V outlet for the dryer, not that we plan on using it much but.... also thinking of the well too...

So how do you do the 120/2440 wiring in a Dist box when you only have 120V (inverter and Gen) incoming? Did you use a separate Dist panel for the Xformer?

Cariboocoot

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

westbranch wrote: »

'Coot, a bit of a technical question/sidebar discussion on this topic please.

WE (the royal we) are in the midst of having the electrician doing the wiring at the new place and now want to wire in a 220V outlet for the dryer, not that we plan on using it much but.... also thinking of the well too...

So how do you do the 120/2440 wiring in a Dist box when you only have 120V (inverter and Gen) incoming? Did you use a separate Dist panel for the Xformer?

Well I don't need a distribution panel for one item: the 120 VAC goes in to the transformer and the 240 VAC comes out the other side. This was an old beast I had laying around and it works fine.

If you're running one of the OB transformers they do make a box for it; just run a suitable 120 line in and 240 line out to the outlet. The output may be required to have its own breaker (and cooling fan): OB expensive box includes breaker http://www.solar-electric.com/psx-240.html

Personally I don't think the output side needs one. If that's overloaded so will the primary be and that breaker should trip.

Having fun with the T-storms knocking out my sat connection every so often.

westbranch

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

Thanks Marc.

I'll talk to the electrician about it, he has a a fair bit of solar system experience out West but we are his first 120V only PV/gen house that are looking forward to the/a possibility of needing 240V. Most he sets up with inverters capable of 240v. He likes OB stuff...

Cariboocoot

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

What are you using for an inverter? Technically a dryer outlet is 30 Amp and that's 7200 Watts - 60 Amps on the 120 Volt side. The dryer itself will not necessary draw that much of course.

treed678

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

This wouldn't address the well pump, but you might look at 120V or different dryer products to avoid such a big load. Personally, how fast clothes dry is about #2,179 on the list of things that must be done as quickly as possible. I wouldn't wanna do a lot of work to dry clothes though.

If the well pump is low wattage I'd look for a lower power, less expensive transformer. OTOH, you could run about anything with the heavy duty OB transformer so that might be handy.

westbranch

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

my starter inverter is a 24V Cotek ST1500W inverter.
I have 2 pumps 240V a 1/3 hp and a 1/2 hp pulled from our well as it was deepened here in town. Both pull about 4 amps each leg, a replacement will be in the 9 - 10 A range. But now I only have a 15 foot head (was >90 ft.) and either pump is way over what I need.
We already have the Bosch stacker set and SWMBO is in love with it...'nuff said. I agree on its prioriy in the scale...

vtmaps

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

treed678 wrote: »

you might look at 120V or different dryer products to avoid such a big load. Personally, how fast clothes dry is about #2,179 on the list of things that must be done as quickly as possible. I wouldn't wanna do a lot of work to dry clothes though.

Lowering the heat on an electric drier means more time tumbling. More time tumbling means more wear on the clothes and lint in the filter.

--vtMaps (with clothesline, no drier)

treed678

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

I'm jealous of you all after parting with my signature list. Anticipation of rebuilding is driving me nuts.

vtmaps wrote: »

Lowering the heat on an electric drier means more time tumbling. More time tumbling means more wear on the clothes and lint in the filter.

--vtMaps (with clothesline, no drier)

Good point. What do you do with the small items? Hanging them seems tedious. I wonder if a net or perforated tray, maybe with a fan above or below, would work well. I saw a product called BreezeDry(?) ...a dehydration closet basically... but it's big and I imagine it costs a fortune. Basically all that's needed is air movement and time.

westbranch

Re: Charging a higher voltage bank than a PV panel or string? (and a bonus question)

this is the ultimate in high tech...a Clothes Horse...http://en.wikipedia.org/wiki/Clothes_horse, we have 2 but not at the cabin, yet..
followed by this http://en.wikipedia.org/wiki/Clothes_line, but there are no trees within 60 feet or so for fire protection....8)