Help...Newbie in town...two cheap inverters on one battery bank ?

Re: Help...Newbie in town...two cheap inverters on one battery bank ?

Welcome to the forum.

You've got a few problems it seems.
As inetdog said much depends on what the loads are drawing. But two things to avoid: adding a second inverter and/or attaching an inverter to the charge controller's LOAD terminals. Here's why:
A second inverter will have its own power consumption, effectively increasing the load on the batteries. This won't make anything better.
No inverter should be connected to LOAD terminals because they are current limited, usually at 20 Amps which is only 240 Watts.

Now onward. On a 12 Volt system wiring size is critical. If it is not large enough the Voltage at the inverter input will drop under load, possibly to the point of triggering th low Voltage alarm. It sounds like this is happening. It also makes a difference how the wiring is connected with two batteries. For optimum performance see method #2 on the Smart Gauge page: http://www.smartgauge.co.uk/batt_con.html

Another thing: if the batteries are not fully charged they will not be able to operate at the higher end of their Voltage range. If all you are charging 230 Amp hours of battery with is two panels totaling 150 Watts they aren't being properly charged. That much panel probably would handle 85 Amp hours @ 12 Volts. Together they might make 8.5 Amps; a mere 3.6% rate - far below the recommended 5% no load minimum.

As it is if the batteries are fully charged they'd have about 1.3 kW hours of stored power. 150 Watts of panel would only supply perhaps 500-600 Watt hours, or about half what the batteries are capable of.

Re: Help...Newbie in town...two cheap inverters on one battery bank ?

Oh goody: a solar "kit".

Begin MOCK MODE:

Part 1: How To Waste Your Time, Effort, And Money Building Panels From Rejected Cells Found On E-bay. You can build your own homemade panels for around 5-6 times as much as a commercial panel costs, and it will have a very high percentage rate of failure (if it works at all) probability with the added detraction of no warranty.

Part 2: Throw away more money on an AIMS MSW inverter.

End MOCK MODE.

That article is out of date in its information, overly simplistic, and useless.

1kW of good panels can be counted on for 2 kW hours of electric in some locations, but the particular location will determine how much power you can actually realize. To make flat statements that "so much" panel will run "this" for "so long" is inaccurate. For one thing, loads run off the batteries, not the panels. The panels recharge the batteries.

The batteries mentioned: two 92 Amp hour 12 Volts totaling 184 Amp hours. The most they would supply would be about 1 kW hour AC. They would serve longer at half that rate. You wouldn't need 1 kW of panels to recharge them either: more like 315 on a PWM controller.

MSW inverters are pretty much a waste of money these days. The pure sine wave versions have come down in price to where they are a better deal as they will handle any type of load providing the power requirement is met.

Expressing the system in terms like having $55 to spend on wiring ... Not good. Every system is different, and you don't know what the wiring needs to be until the rest of it is planned.

Perhaps the worst statement in the article is this: "... it is relatively easy to expand ..."
In a pig's eye it is. Half the questions I answer have to do with expansion and how difficult it is to do once you're locked in to a lower system Voltage. Then there's the problem of finding equipment now that is compatible with what you bought then: panel specs tend to change often these days and mixing them isn't always possible. Most of the time expansion is a matter of starting all over again.

My advice: read the forum, ask questions whenever you like. That's why we're here. An active forum full of engineers, technicians, installers, and people with experience is going to be far better than any single source written by one person.

Re: Help...Newbie in town...two cheap inverters on one battery bank ?

The inverter should be close to the batteries as they are what power it. The longer the wire between batteries and inverter the greater the Voltage drop under heavy current loads and the more likely there will be trouble (such as the Voltage at the inverter falling below the cutoff point even if the batteries are charged).

Next to the "Reply" button is one that says "Reply With Quote"; that will quote that post in your reply.

Re: Help...Newbie in town...two cheap inverters on one battery bank ?

In this case "bolted up" means solid connections on the DC wiring. Good connections are important to keeping the DC input Voltage steady under loads. It's easy for resistance to go high and on 12 Volt systems it can cause big problems.

Your 3.5mm wire is roughly 7 AWG, which is good for around 60 Amps tops or 720 Watts from the inverter. The closer the current draw is to this level, the greater effect any loose connections or high resistance points will have. If you can't get steady output Voltage with no load on the inverter, something is seriously wrong. At that point you start checking everything, from the resting Voltage of the batteries to the Voltage difference between them and the inverter input.

BTW, adding another panel whose Vmp is only 15.84 is not going to help much: by the time its output goes through wiring the Voltage it supplies will be less than the battery charging point. This is why "12 Volt" panels have a Vmp of 17-18.

You can upload digital pictures by clicking "Go Advanced" and "Manage Attachments". Use the "Basic Uploader" to find the file on your computer, send it to the server, and include it in your post.

Re: Help...Newbie in town...two cheap inverters on one battery bank ?

Okay that wiring could do with a bit of re-work.

Think like this: you have four separate but inter-acting circuits: The first is the PV's to the charge controller, the second is the charge controller to the batteries, the third is the batteries to the inverter (and other DC loads), and the fourth is the AC wiring. Each of these will have its own Voltage and current ratings and needs to be wired accordingly (including circuit protection).

Basic wiring rule: it has to be large enough to A). carry the maximum expected continuous current and . conduct the Voltage over distance under load without incurring too much Voltage drop. The circuit protection is then determined by the wire size.

Right now the DC out of the controller and in to the inverter is wired together. This won't "bypass the batteries" exactly, but it's the same size wiring and probably shouldn't be. If the controller is 30 Amps, then the most current seen on that circuit (#2) would be 30 Amps. That on the inverter translates to (30 * 12) approximately 360 Watts. Is that a 500 Watt inverter or a 1500 Watt inverter? Either way, the 10 AWG that would work for the charge controller output is too small for the inverter draw. This can cause Voltage drop under loads. At 500 Watts the wire size should be at least 8 AWG, and larger is always better on an inverter.

So what you're looking to do is:

1). Circuit from panels to charge controller. If more than two panels in parallel each should have its own fuse. Wire sized to handle combined current of panels and (especially important here) not lose too much Voltage over distance.

2). Circuit from charge controller to batteries. Wire and circuit protection to handle maximum current. Voltage drop is usually not an issue here so long as the distance is kept to a minimum. Fuse/breaker according to controller's rating.

3). Circuit from batteries to DC loads including inverter. This will be two circuits for you; one wire set and fuse/breaker large enough to handle the inverter and another for your DC chargers. Voltage drop can be an issue here especially for he inverter as it will draw a lot of current at maximum power. It is best to have the fuses/breakers near the battery so that if one does blow there is not a lot of "live" wire about looking to make a short circuit and cause more trouble.

4). AC lines. Standard household wiring practices apply here.

Does this help?

Re: Help...Newbie in town...two cheap inverters on one battery bank ?

It's a bit difficult to draw diagrams because I'd have to do a new one for each system. Otherwise I'd be drawing "basic" diagrams which could get misinterpreted - and inevitably someone would say "you left out ..."

Although I know I should draw some of these basic diagrams and then "just point". :roll: