superdiy

The more the losses in the mosfets (Ron), the more heat they generate and the bigger the heatsink(s) required to keep them cool.

Apparently they don't sell the 702, only the 700 when I inquired. What do they ask for the cables?

Where are you situated? You can try www.ontrack.co.za, they had the best price on the BMV702, www.rectifier.co.za came in with a R100 more. I don't know whether any of the 2 sell the cables, but both are local Victron agents. Looks like I need to start assembling these cables - opportunity to make some money.

I've came across a post in an overseas forum the other day where someone mentioned a 12V10KW inverter.

I agree with some of the things you've mentioned and would like to add the following. The battery voltage of the UPS/inverter will depend on a lot of things, not only on replacement price of the batteries. 24V in terms of batteries does not equate to 2 batteries and 48V does not equate to batteries. A battery bank can consist of 2V cells or 4V, 6V, 8V etc. batteries and you can even have multiple strings of batteries in parallel. Back to the inverter battery voltage... An important thing to keep in mind when deciding on the system voltage / battery bank voltage is the size of the inverter. The bigger the inverter the more current would be drawn from a lower voltage battery bank than from a higher voltage battery bank for the same inverter output. Here is a comparison without including any losses etc. If you draw 3000W from a 24V inverter, you will draw approximately 3000/24 => 125 ampere from the battery bank. If you draw 3000W from a 48V inverter, you will draw approximately 3000/48 => 62.5 ampere from the battery bank. In real life you rather want to draw less current from a battery bank for various reasons which include the following: The batteries are discharged at a lower rate and will last longer per cycle. For the same reason running the inverter for a specific amount of time the batteries on the lower voltage inverter will be discharged (DoD) more than the batteries on the higher voltage inverter. The battery cables on a higher voltage inverter can be thinner and accessories like fuses and fuse holders etc. will also be cheaper because they don't need to handle such high currents. The connection and electronics inside the inverter can be designed to handle lower currents in the higher voltage inverters which can also result in a lower purchase price for the inverter. Most of the time small inverters <2000W are designed to work on 12V, medium sized inverters 2KW-3KW are designed for 24V and bigger inverters for 48V or higher. Bottom line is that inverter sizes (KVA or KW) usually determine the battery bank voltage.

Not entirely true. Some inverters use high frequency switching (e.g. 100KHz), as in a switch mode power supply and others use low frequency (typically 50/60Hz). The transformers used in HF inverters are small and very light compared to the transformers used in LF inverters of the same rating. These inverters using HF are also sometimes referred to as "transformerless", becauae of the small HF transformers used. Obviously the bigger transformers contain more metal (iron and copper) than the small transformers used in HF inverters and that will influence the weight. The HF inverters are newer technology, which was perhaps not around in the "old toppie's" younger years, but it is not a true measurement of how "long it can operate under load".

It is totally dependent on the type of installation. Stand alone / off grid installations and installations where the whole house is connected to the inverter and the inverter AC input is left unconnected are not a problem. Installations where a part of the installation is powered by the inverter and the inverter is used as a UPS is still a problem. If you are referring to the second type of installation your installer probably do not want to go into detail because he also does the connection it in a certain way which either satisfies SANS or the E/L test when issuing a CoC. Currently we were unable to get a solution which satisfied both SANS and the E/L test required for a CoC in this type of installation. There are 2 possible solutions however, but it is not clear if any one of the two would satisfy the SANS regulation.

Fuses are perfect. When a fuse goes open circuit and needs replacing, there are in any case no current flowing and when you open the fuse holder it will no arc. Regarding the battery fuse: Switch off the inverter and use the bulb trick to slowly charge the capacitors in the inverter before closing the fuse holder after fuse replacement - that will prevent the arc when you close the fuse holder. Regarding the PV fuse: Switch off the inverter and just close the fuse holder after fuse replacement - the current is much lower on the PV line and will not cause such a big arc. Alternatively wait until sunset and then replace the fuse. Battery fuse holder: CMS2258.1 Battery fuse: 2258.100 PV fuse holder: 211PV PV fuse, depending on string current: 10A: 30F10PV 12A: 30F12PV The fuse should have a rating of 25% more than the continues current through it, to avoid nuisance blowing.

Thanks John, when I (one day) develop the requirement to log the BM, I'll experiment a bit more.

It depends if it is a line interactive or online design. Online UPS inverters run all the time. Line interactive only kick in when required.

Regarding the access usage of the inverter I cannot really comment. Claims were made that the infini also uses a lot (250W) on idle. I've bought a din rail meter with digital V, A, W, VA and pf readouts. Plan is to install it next to the changeover switch in a surface mount DB, but in-between the infini and the mains connection in order to do some measurements regarding power consumption by the infini as well. I'll post the results once I have them.

The Axpert inverters cannot feed back to the grid. Yes, some prepaid meters can measure flow in both directions.

Good question. You can install the "horizontal" pieces of unistrut at a slight angle to ensure that water always run out the open ends.

I've also googled a bit just now and came across a few posts, but none mentioned any detail except for pinouts when connecting it to a PI. I've built a USB to DMX "cable" a while back and used a FT232, but I've also added an ISO7220 for galvanic isolation. I think it would maybe be a good idea to do the same in this instance. Which FTDI chip did you use?

This sounds familiar

That might be a way of temporarily "disabling" the internal charger.

If the inverter is still connected to the utility, and operated as a UPS the utility power will still charge the batteries - the internal charger can not be disabled and it will compete with an external charger. If you however use the Axpert as a stand-alone unit, NOT EVER CONNECTED TO THE GRID OR PV PANELS, you can use an external charge controller and use the Axpert as an inverter only.

Problem is that you cannot disable the charger on the Axpert, so the two "chargers" will compete. The other problem with having a separate charge controller is it might be trying to charge the batteries while the inverter draws power from the batteries at the same time which would also cause problems.

Looks like a great product. Anybody know of a local supplier?

Is that the price of a T105 or T105-RE? Quite expensive for T105's. Last price I got from batterypitstop.co.za was R1755.60 incl. VAT - that was in July.

Hi John I don't have 105's or an Axpert. I did an installation for my dad where I've used T875s on a 24V Axpert. Unfortunately the Axpert inverters are not the best type of "chargers" to use with Trojan batteries and not with small battery banks (200Ah-300Ah) either. According to the Trojan datasheets the bulk charge setting for a 24V bank should be 29.6V and for a 48V bank it should be 59.2V. Unfortunately the 24V Axperts can only go up to 29.2V and the 48V Axperts can only go to 58.4V. You'll have to set setting 5 (Battery type) to USE (User-Defined) and setting 26 (Bulk charging voltage) on the Axpert to its highest possible value and setting 27 (Floating charging voltage) to 26.4V on the 24V Axperts and to 52.8V on the 48V Axperts according to the Trojan datasheets. The ideal charge rate should be between 10% and 13% of the battery's 20-hour Ah capacity. For one bank of T105s, that should be between 10% of 225 => 22.5A and 13% of 225 => 29.25 - I would suggest to set it to 25A, but since the Axperts only have 20A or 30A options, I'll use 20A. Setting 2 (Max charging current) should be set to 20A or 70A for the 4KVA and 5KVA Axpert models. Setting 11 (Max Utility charge current) should then be set to 20A. Hopefully you don't have (a lot of) PV panels installed, because you cannot lower the solar charge current and the 60A (minimum) is extremely high for a 225Ah battery bank.

Yes, I've used it. Check the photos in the gallery.

PM'd you.

Can you also supply a HydroLink Watering System for a set of 8 x T105-RE's and for a set of 3 x T875's. Please quote on both.

Hopefully that is the next owner's problem in 20 years' time. There will be other ways of getting them out, but as I've said, the idea is only to retard the theft process.