Hello from Adelaide! + question about charging

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Hello from Adelaide! + question about charging

Postby johnd0787 » Sat Jan 17, 2015 2:10 pm

Hello, I am a self confessed "power freak" and off-grid enthusiast. I have a PV powered 24vdc house power system with inversion to 240vac/50Hz domestic power.

We're currently running 12x Sharp NTR53E3 175w PVs (2.1kW array) charging a 24vdc battery pack via an OutBack MX60 MPPT charge controller. Battery pack is made from 2 strings of 12x Sonneschein 2v cells (making a total battery capacity of 2x 600Ah = 1200 Ah). My house power (240vac/50Hz/single phase) comes from an OutBack VFX 3024E (3kW) inverter / battery charger. I have a MATE v1 connected via HUB4 to the VFX and MX60 and battery’s RTS is connected via the VFX. A laptop is installed in the shed hooked up to my MATE (v1) running WattPlot ‘VisualMate’ software so that I can see what’s going on. I can even see my system status from in front of my TV thanks to smartphone and IPCAM technology :-)

I have a 7.5HP Honda petrol generator as a primary battery charger (output 240vac/50Hz) for when the sky clouds over or its night/party time. I also have an older diesel generator that I am refurbishing with a view to (eventually) using the more reliable diesel as my primary (direct??) battery recharger in the winter months when there isn’t enough sun. I figure I can direct feed my MX's using alternators but thats another story for the Forum!

PV upgrade in progress: I’m adding 6x Trina Honey 250w PVs feeding the same 24Vdc battery pack via their own FM80 MPPT charge controller. The two OutBack charge controllers will run in parallel (synchronised via MATE) and connected via the HUB4. Battery monitoring will be performed via a Xantrex LinkLITE “fuel gauge” meter. This is a work in progress..... (!!) :P
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Re: Hello from Adelaide!

Postby Gordon-Loomberah » Sat Jan 17, 2015 2:43 pm

Welcome to the Energy Matters Forums John :)

It's always great to see another off-gridder join the forum!
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Re: Hello from Adelaide!

Postby johnd0787 » Sat Jan 17, 2015 4:06 pm

Hello Gordon & EM Forum folks! Its great to be here and chatting with like minded people about important things - like off grid power!! :D

I have been trawling the forum today and there may be some good ideas that I can directly to use. You will notice that my "intro" talks about adding a 'direct charge' / engine-alternator set up. This is because I have barely enough PV to charge my batteries if its cloudy and often in winter resort to longer than I would like generator runs.

My question then: what would be a good arrangement for motor-alternator charging of my 1200AH 24vdc battery pack? I have an idea I can use one of my charge controllers (say the MX60) to (as usual) charge the battery pack with the input to the MX60 coming form the alternator.

Is this the best way to achieve a nice ABSORB/FLOAT on my batteries? Looking forward to your thoughts? I have an 11HP diesel and a 10HP petrol engine to spin the alternators.

Thanks.... :geek:
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Re: Hello from Adelaide!

Postby Gordon-Loomberah » Sun Jan 18, 2015 1:17 pm

johnd0787 wrote:My question then: what would be a good arrangement for motor-alternator charging of my 1200AH 24vdc battery pack?


I've only ever used a motor driving an alternator to charge batteries, although most seem to use inverter-chargers that require 240V input- an unnecessary arrangement IMHO. Alternators are reliable and easy to get parts for, and maintenance such as brush replacement is easy. Even diagnosing and replacing a blown diode is pretty straightforward if you are handy with a multimeter and can solder.
Back in the days when I had a 24V (1200AH then 800AH) Lead-acid battery I used a 30A truck alternator belt driven from a small Honda motor. I ran this through a SB50 MPPT charge controller (50A 24V, Max Voc 68V), to get up to 50A from the 30A alternator, by allowing it to run at around 40V, instead of being limited to battery voltage.
For a bit more grunt, 80A or 100A 24V truck alternators can be found at wreckers for a reasonable price- just check the brushes and put in some new bearings and they are generally good to go.

Since going to LiFePO4 (400AH @52V) their superior efficiency has meant that I have had no need for generator charging- just as well, since I dont have a suitable generator!

Is this the best way to achieve a nice ABSORB/FLOAT on my batteries? Looking forward to your thoughts? I have an 11HP diesel and a 10HP petrol engine to spin the alternators.


Short answer- not really. Dont waste fuel doing Absorb (apart perhaps just early stage Absorb for a bit of gassing electrolyte agitation action in flooded cells), just use it for Bulk charging to bring it up to Vabsorb, as it will be fuel inefficient running the motor at very low loads, and not good for the motor in some cases. Use the genny for Bulk, finish off with solar if you can, but don't worry about getting all the way up to 100%SOC every day, otherwise you'll get sick of listening to the motor running, belching fumes into the atmosphere. If you can add some more panels to get you through cloudy weather, you can cut back on generator use significantly.
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Re: Hello from Adelaide!

Postby Bthree » Sun Jan 18, 2015 1:35 pm

Gordon-Loomberah wrote: If you can add some more panels to get you through cloudy weather, you can cut back on generator use significantly.


And Gordon says also .....

"As far as adding more panels goes, have a read of this thread: solar-wind-gear/topic5064.html
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Re: Hello from Adelaide!

Postby johnd0787 » Sun Jan 18, 2015 4:23 pm

Gordon,
Thanks for your post this is very encouraging. I rather like the idea of a running an 80A alternator off my 11HP diesel to produce a BULK charge :) . I have two questions if I may apologies if they are dumb questions - I am not electrically trained;

Q1- I assume that the (quite high) amperage from the alternator cannot be simply run in parallel with whatever is contributed from PV in case daylight/alternator combination causes an over-amp situation with the MX60 charge controller? If this is the case would you suggest adding a manual switch at the input to the MX60 so that I could either run as normal on the PV (day scenario) or divert to the alternator (evening bulk charge scenario)?

Q2 - For a 24v battery system I assume that the MX60 would need to see a voltage from the alternator quite a bit in excess of 24v. I think this is why you modified your alternator to provide a 40v output? If this is true I'm going to have to perform some alternator voltage-regulator mods also. Any thoughts on what I should go looking for in a second hand 24v 80a truck alternator as well as the v-reg mods themselves?

Thanks - much appreciated. I hope the above makes sense. Enjoy the fantastic solar weather! :D
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Re: Hello from Adelaide! + question about charging

Postby Gordon-Loomberah » Sun Jan 18, 2015 5:21 pm

If you can score an 80A alternator, there's no need to run it through a regulator, and it may well damage the regulator, as the FM80 has a max input current of 64A, and the MX60 is no doubt something under that. If you can only find a 40A or less alternator, then it could be run through either charge controller. Just don't run it in daytime, to be safe with your CCs. The rectifying diodes on the alternator output mean that it won't draw any reverse current during the day. I removed the alternators regulator and ran a short length of Nichrome wire in series with the field winding to reduce the current to a satisfactory level (since I was running it at 40V instead of ~28V).
I ran my 30A alternator in parallel with 5 panels and a wind generator, but only when the PV wasn't producing anything, or perhaps an amp or 2. As the alternator heated up, the output current would drop, down to a bit under 45A going into the battery, and it happily worked in parallel with the WTG at night when it wasn't too windy.

No mods required to run the alternator at higher voltage, just spin it fast enough. Voltage is dependent on
RPM, but if you load it up the voltage will drop and current rise, but the current is limited by the temperature rise of the alternator windings (and diodes). Hot wire has higher resistance, so output current drops when you have it maxed out.
Alternators are wound so that sufficient voltage is produced at car engine idle, say 750RPM, * say 2 for pulley ratio, so you only need ~1500RPM to get to ~28V.

Yep, 3 days of sun in a row, but I've been too busy doing other things (like catching egg stealing goannas and driving them a long way away!) to make use of it all :)
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