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oldspark battery bank w/possible solar


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oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 22, 2012 at 2:13 AM / IP Logged  
Parallel relays...
With fuses for each relay?
For (legislated) AC stuff, that takes special approval. It requires matched contacts and cable resistances to ensure current sharing.
And then if one fails or switches slower so the others take the brunt...
Admittedly the example I am thinking of involved using 3 breakers instead of one for physical reasons. But they were breakers (contactors) so that if overloaded, they would trip off.
Your equivalent is to have each relay fused, though I'd suggest (self-resetting) circuit breakers because short duration high currents are not uncommon when connecting batteries. (And whilst relay contacts and cables may handle it, normal fuses won't.)
There can also be a contact issue if relying on NC contacts. They do not have the electro-magnetic force that keeps them together - merely the spring force. (Hence why NC contacts generally have a lower current rating than NO contacts.)
Multiple relays may also consume more power than their larger counterparts.
I sense a false economy here, but you can suck it and see...
At least using relays between the paralleled batteries negates the need for those long runs to your central switchbox, it should only be one cable for each polarity per bank - ie, 4 cables. (Arguably 3 if one bank is locally grounded.)
But then the series/parallel switching relays can be local too - no need for those 4 cables either...
I'm not sure how using a latching control relay will save much power. Using latching relays for all makes sense, but then there is their cost. (Though I was able to buy 80A SPST latchers for ~AUD$5.)
But I assumed that compared to the load currents, the relay power would be negligible. And the same when charging.
If the load is low, take it from a single battery.
And keep in mind that equal paths is more than equal cabling - it's how they are interconnected. That link I provided compares the cases of 2 and 4 batteries in parallel.
two12 
Copper - Posts: 84
Copper spacespace
Joined: November 24, 2009
Posted: April 02, 2012 at 12:48 AM / IP Logged  
cool van man!
I have a smaller set up that includes 3 AGMs for a total of 360ah but each is isolated.
the only thing I can add that may be of some help here is that I would add at least one solar panel and reputable charge controller just for the sake of battery health/fitness. the modern solar charge controllers are way beyond any other method of charging.
I have 350watts on the roof mounted beteen and just bellow a four yakima brand roof racks, they are mounted in such a way as I can still utilize the roof racks.
I also use a Honda 2000 generator for back up but it is not mounted anywhere just portable.
the problem with trying to actually rely on solar panels is they have to be in the sun so the van will get hot inside in the summer if you have to park it in full sun.
but it will really help your batteries to get at least 100watts worth of PV and a decent PVM solar charge controller just to keep them in tip top shape.
the is also a pretty good AC to DC automotive charger out now too that comes close to solar charging capabilities, it is the black & decker "VEC1093DBD" this combined with a decent inverter/generator (pure sine wave) is the best set-up I have found.
for battery status the Victron BMV 601 series monitors are the only thing I have found to be reliable. it monitors amp in/out and keeps track.
this monitor also logs data and so will the decent solar charge controllers so you will know exactly how the batteries are doing any time.
a homade generator might be oK for bulk charging but be sure to finsih that off with something else.
good luck with the van and keep us posted!
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: April 02, 2012 at 5:40 AM / IP Logged  
two12 wrote:
the modern solar charge controllers are way beyond any other method of charging.
I'm curious how you justify that.
PS - meltmanbob is aiming for cheapness. Solar was an OP suggestion, albeit to power rather than trickle & float charge.   
And I'm glad you too isolate your batteries. Too many learn the hard way!
two12 
Copper - Posts: 84
Copper spacespace
Joined: November 24, 2009
Posted: April 02, 2012 at 8:44 PM / IP Logged  
oldspark wrote:
two12 wrote:
the modern solar charge controllers are way beyond any other method of charging.
I'm curious how you justify that.
from what I have found the solar charge controllers have way more sophisticated/advanced charging algorithms.
they also keep a float charge going as long as they have sunlight.
many are programable and you can input the specs exact from the battery manufacturers.
there are also true deep cycle batteries specifically designed for solar intsallations but these are not recomended for mobil aplications.
hey Oldspice, while I have your attention, I could really use your expertise again on this topic: https://www.the12volt.com/installbay/forum_posts.asp~TID~131100~get~last#655101
thanks
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: April 02, 2012 at 10:16 PM / IP Logged  
Thanks for qualifying...
But normal "intelligent" chargers should have the same capabilities, and do not suffer from the solar situation of insufficient charge current AT LEAST once per day (ie, at night & whenever insufficient solar panel output).
I think normal intelligent chargers still lead the technology and solar follows. Solar merely change the chargers front-end (panels, MPPT etc).
And though multiple charger re-connections itself is questionable, if the charger were always to initially connect in bulk mode (not float mode). I'm sure that would be considered detrimental. (Not all chargers have a "memory" that continue their mode after a power outage.)
FYI - Solar, though expensive, can be good as an "unpowered" trickle charger. But batteries for high power applications like this thread are very expensive and inefficient (and anti-green) as it is, adding copious solar probably makes that far worse.
As to deep cycle batteries, I like what I read this morning at otherpower.com - namely that there are no "deep cycle" (lead-acid) batteries, merely batteries that withstand deep cycling better. And they too say NEVER lower than 50% but preferably under 20% discharge.
[That otherpower link is to their battery comparison page despite their totally wrong specs on the D7 battery (probably obtained during older political propaganda days).]
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: April 04, 2012 at 8:18 PM / IP Logged  
meltmanbob - FYI - I happened upon a Trojan L-16 discharge table (SOC vs voltage) here otherpower.com - battery metering.
Note the lower voltage for ~11.9V for 0% capacity - ie, a 0.8V difference between 100% & 0%.
I mention that because I usually write of my simple "10% per 0.1V" ROT as being conservative, but that is based on a ~1.2V range - ie, 12.67V to ~11.5V (wet cells).
(And I think I mentioned that ROT in this thread.)
Note too what OtherPower say about not discharging more than 20% and never more than 50% without recharging. And that discharging 75%-80% WILL cause damage even if deep-cycle batteries.
[ I don't disagree, but essentially all discharges damage to some extent (except as required for "exercise", and noting small discharges are negligible or normal), but that's a complex area and very dependent on factors like how soon they are recharged etc. ]   
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