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Author Topic: Voltage settings for forklift batts  (Read 7263 times)
EccentricAnomaly
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« Reply #15 on: December 23, 2010, 11:16:22 AM »

It may even be worth having a small, cheap 100Ah battery as a "sacrificial buffer battery" that allows the main bank to continue float charge (using a small 250W inverter / charger) after you've switched off the generator.

Not cheap but probably not sacrificial either would be to use some sort of LiFe battery for this function.  They like being at least partly discharged.
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stephendv
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« Reply #16 on: December 23, 2010, 12:50:54 PM »

Thanks for all the input.  I'm going to stick with pure gen charging - no sacrificial additional battery as I'd rather spend that money towards solar panels in the future.  The batteries will never be float charged, the gen will turn off when absorb is done. 

My initial thoughts about battery usage for the next few months were a bit off.  Since they will only really be used while building the cabin for the odd power tool, there will be very little load.  Usage will probably look like this:
- Full charge on Sunday, with a 5 hour absorb, and I'll check SG periodically, if it stops rising over 2 hours I'll note the absorb time and use this + 30 minutes for the next absorb.  Battery will be at 95-100% SoC on sunday night.
- No or minimal load for the week, inverter completely off.
- Should reach saturday with at least 80% SoC.
- Could draw down to 75% SoC by sunday, do a boost charge to bring it to 90%, shorter absorb, maybe 3 hours.
- As above, no or minimal load during the week so they'll be at 90% ish during the week.
- Do a full charge with 5 hour absorb on sunday, i.e. 2 weeks between full charges.

So sticking with the original plan of doing a 2 week interval of full charging, but will spend most of their idle time during the week at at least 85% SoC, then drawn down to 75% on saturdays at the worst (very liberal, realistically I think it would be 80%), then full charge every second sunday, and boost charge every other sunday.

Sensible?

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Justme
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« Reply #17 on: December 23, 2010, 02:14:58 PM »

The long periods of inactivity at low soc will cause sulphation. Could you not fully charge just before they go inactive so that they stay stored at a higher SOC?

Using the one charge cycle to then calc the other absorb times is also risky. Its what the adaptive charge setting does on the Victron. Basically if you charge for x hours at bulk it will then absorb for Y hours. As the bulk time comes down so does the absorb time.

BUT & its a BIG BUT the faster you charge the longer the absorb needs to be. A lo ng slow bulk phase will need a shorter absorb, a hard & fast bulk needs a long & slow absorb. Adaptive does it the wrong way round.

I would look at solar panels. Do the bulk on the genny & the absorb via the PV. Your not going to get the max kwh out of the PV but you will save on fuel.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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« Reply #18 on: December 23, 2010, 02:22:48 PM »

The long periods of inactivity at low soc will cause sulphation. Could you not fully charge just before they go inactive so that they stay stored at a higher SOC?
Yep, that's exactly the idea - maybe I didn't explain it well.  They'll be charged to at least 90% SoC every sunday and left virtually untouched for the week.  Then full charge every other sunday.
I would look at solar panels. Do the bulk on the genny & the absorb via the PV. Your not going to get the max kwh out of the PV but you will save on fuel.

Yeah, will definitely get the PV panels in a few months once the cabin is done.  Don't want to install them yet because the location is quite isolated and it's thieving season.
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Outtasight
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« Reply #19 on: December 23, 2010, 10:59:52 PM »

Another small factor to consider is that lead-antimony flooded cells will self-discharge by around 5-10% a week, just by sitting there, doing nothing, with no load on them!  A bit slower in the cold weather but faster in warm conditions.  A small solar panel will at least compensate for the rate of self-discharge.  If they're lead-calcium types then they self-discharge less (more like 3-5% a week).

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Justme
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« Reply #20 on: December 24, 2010, 11:04:10 AM »

The long periods of inactivity at low soc will cause sulphation. Could you not fully charge just before they go inactive so that they stay stored at a higher SOC?
Yep, that's exactly the idea - maybe I didn't explain it well.  They'll be charged to at least 90% SoC every sunday and left virtually untouched for the week.  Then full charge every other sunday.
I would look at solar panels. Do the bulk on the genny & the absorb via the PV. Your not going to get the max kwh out of the PV but you will save on fuel.

Yeah, will definitely get the PV panels in a few months once the cabin is done.  Don't want to install them yet because the location is quite isolated and it's thieving season.


I was talking about leaving them at 90% for the week. If they are going to be left then fully charge them. Start at 90% take away the self discharge add in the sulphation and each week you are prob going to permanently loose a % or 2 of capacity & a few charge cycles of life. Once you have the PV it wont be so bad as they will (apart from in winter) if sized right stop the self discharge & finish off the full charge cycle.

Just to be clear, what ever you do with a battery is wrong for its capacity & life time / cycles. Even bats that are on float 24 / 7 die in the end. All you can do is do the least damage possible. Its hard but you need some sort of scale of use over cost over bat life & replacement costs to get a "best" for your install & usage. My target is to use less than 500 of Red per year (mostly in the winter) in the genny & have a bat replacement cost of less than 100 per year (we have spent about 550 on bats [used forklift cells] so far & are at year 2.5 & still on the first bank that cost 127, the other bank that is bigger & for the cabin when its finished gets floated when the genny is on to keep it in good condition). This year will be over budget on Red due in the main to building the cabin which needed the genny on in the summer but also to the extra long winter we are getting. 
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
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