v-lux wrote:
Bear in mind also that the main part of this charging will take place in the early stages (batteries suck up lots of power when they're empty) and amperage will tail off as the voltage increases (slower charging)
with the sterling though the rate will be more linear... eg the battery bank might be capable of sucking up 400a or so to begin with... but iwill be limited by the output of the alternator...
even once 75% full the batteries can probably still draw 100a or so (at the higher voltage) so the charging "curve" would be linear due to the bottleneck caused by the alternator
we can also see from the sterling graph that at the higher voltage three times the energy input results in double the energy stored (relative to low voltage charging) - almost certainly this is a result of input energy being wasted as heat
which will mean the useful input charge will be lower than the alternators theoretical max output
Not so, Syncrosimon has the shunt and control unit/display set up running on his Sterling charger and regularly sees over 100a from his 90a alternator. (iirc the peak was something like 112a)
aha.. thats my gotcha backat ya the alternators "rating" is not the same thing as its "theoretical max output" -
though its quite handy to know that the theoretical max output is a bit over 112
youve got to wonder what the implications on the long term health of the alt is from being run so hard though
youve got to wonder what the implications on the long term health of the alt is from being run so hard though
Indeed, ive wondered this myself. Sort of feels like it must be putting quite a strain on doesn't it. However, ive been running the same alternator (which is an old bosch unit from an AAZ that i used to have in my van - possibly as old as 1990's?) before i got the sterling and ever since and surprisingly its still pumping out the volts.
At some point i'm going to upgrade to a 120a alternator which i'm guessing will peak at about 140a (ish) which will cut the charging time down rather nicely!
Just to add = I think some of you might be forgetting one thing.
The Sterling converts whatever voltage (within reason) that is put into it it to an output of 14.x volts to provide a high rate of charge output. ie it has a voltage "step up" function a bit like an inverter (but in this case DC in and 14.x volts DC out).
The Sterling cannot distinguish between voltage from the alternator and the starter battery as these are hard wired in parallel.
So, it is quite capable of using the starter battery as it's source of input voltage and the starter battery is capable of 100's of amps of output. Therefore the Sterling's output is not limited to the output of the alternator. The Alternator is merely running flat out to try to keep up with what the Sterling is taking out of the system as a whole.
Note = I am not familiar with the finer workings of a Sterling charger, but I do have 35 years experience of working with electronic power supplies etc.
i would have thought that, though hardwired, there would be a +2v PD between the alternator terminals and the battery internals, thereby stopping any current flowing from the starter batt through the alt to the leisure batt ??
trentjim wrote:i would have thought that, though hardwired, there would be a +2v PD between the alternator terminals and the battery internals, thereby stopping any current flowing from the starter batt through the alt to the leisure batt ??
Nope.
The only way you can have a PD between alternator and main battery is if the wire has resistance and a current is flowing. As the wire is very heavy and very little current is flowing under normal circumstances then the voltage at the alternator terminal and the battery terminal will be the same = Easy to prove with a digital multi meter.
When the split relay is on, as in when the engine is running, current DOES flow from the starter battery (and alternator, because to all intents and purposes they are one and the same as far as voltage and current are concerned), to the leisure battery. The alternator then "shares" it's output between the two.
[quote="ghost123uk] The only way you can have a PD between alternator and main battery is if the wire has resistance and a current is flowing. As the wire is very heavy and very little current is flowing under normal circumstances then the voltage at the alternator terminal and the battery terminal will be the same = Easy to prove with a digital multi meter.
[/quote]
youre thinking about pd at the wrong place - the battery terminal is to all intents and purposes the same as any point along the wire - the potential difference is between the alt and the cells.
if there were no pd no current would flow and no battery would ever charge - ohms law my friend
a splt charge systems does indeed connect the two so current can flow - but we are talking about a sterling here (hence the +2v pd) which uses MOSFET wizardry to stop juice going the wrong way (at least as far as i understand it)
trentjim wrote:
youre thinking about pd at the wrong place - the battery terminal is to all intents and purposes the same as any point along the wire - the potential difference is between the alt and the cells. If there were no pd no current would flow and no battery would ever charge - ohms law my friend
Aye, we were talking at cross purposes.
When you say "the potential difference is between the alt and the cells" then I took it to mean the +ve terminal on the alternator and the +ve terminal on the battery (no PD)
However when you say "cells" I guess you mean the internal cells in the battery, in which case you are correct of course = PD
My bad, as looking back you did say "battery internals"
I have a t25 viking newly bought. It has 3 way fridge & mains hookup controled via a cf6 zig unit. It also has a water heater (another post).
At present there is no leisure battery but the wire for one got to behind the pessenger seat.
The 12v supply to the fridge is from the main battery via a dodgy looking relay system working of the ignition and additional switch.
My intention is to put a large leisure battery in a newly constructed bay in the bottom of the wardrobe. Isolate this battery from the mian battery using a smartcom auto change relay. The fridge will draw is power directly from the leisure battery (via inline fuse). I also intend to run the ICE directly of the leisure battery. This would make the centre switch of the zig unit redundant (chage/off) as I don't like the idea that you can connect the main battery to the leisure battery without ensuring both are being charged first. Will this work?
As a newbie to zig units I'm amazed at how much they are considering how little technology is in there. For my own camper I am making my own distribution panel with auto charge, auto mains/ invertor isolation, solar charging. ignoring the solar panel and invertor this panel has cost me £25 (plate, switches, fuses, relays, mains charging transformer). definately the way forward.
@ pfield69 = Most of what you said makes sense, but note the reason the 12 Volt side of the fridge is connected via a relay to the main battery is that it is usual to only have the fridge on 12 Volt when the engine is running. Most fridges use 5 to 10 amps and so would flatten a leisure battery in a few hours. When the engine is not running, the only sensible option is to run it of the gas (very efficient )
if it were mine, I would run from gas, but it is a friends who is a fireman and has heard too many nasty stories of CO poisoning and the like. He will be running it off a 210ahr battery so i estimate it will last 20hrs without a recharge.
I have a cheap table top fridge (TESCO) that cost £70. That draws 10a when running but it will last 2 days on a 120ah bmw battery I had laying around. I make sure its cold on mains before setting off. I guess its how effiecent the fridge is and how long the cooler actually runs. this is also running through an invertor.
Thanks for posting the energy consumption of your table top fridge... its close enough to verify my theoretical 46Ah per day for a compressor fridge running off an inverter. (90Ah usable in a 120Ah battery sounds about right to me)
= Easy to prove with a digital multi meter.
