Alternative to an expensive 3 stage charger
Submitted: Sunday, Feb 20, 2005 at 20:33
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Member - Jimbo (VIC)
About a month ago I bought a Projecta "Chargecontroller BM 140" from Bursonsfor $50. This unit goes between the battery charger and the battery and converts your standard battery charger into a two stage charger. Effectively, it lets your charger charge the battery until it is full and then switches to "float" mode. Also has a switch for using Gel or Wet Cell batteries.
My AGM battery will only get to 12.65 volts (after standing for at least 24 hours to get a realistic reading) when charged fron the alternator. With the Projecta gizmo attached and left for four days, after it went into float mode after the first four hours, and then being disconnected and being left to sit for three days, the batt is still showing 12.91 volts.
For a cost effective way to get a battery fully charged I reckon this is a good bit of kit. Gets the batt fully charged without overcharging it.
Jim.
Reply By: Member - Sand Man (SA) - Monday, Feb 21, 2005 at 21:22
Monday, Feb 21, 2005 at 21:22
Not quite David.
If you use a manual solenoid isolator the batteries will be paralleled together for charging/discharging, so you are correct in this case.
However, if you employ a "diode" type Isolator in a dual battery system you won't have that problem.
(Extract from the Piranha WEB site)
"The diode pack battery isolator completely isolates each battery circuit from the other so when one battery is used (or even dead) the other will remain fully charged. The diode isolator acts as a one way valve between the two batteries, the isolator prevents current from flowing from one battery to another. Each battery is isolated and acts as an independent power source. When charging the batteries, it doesn't matter how drained either battery becomes as each battery is always isolated from the other. The alternator is able to recharge each battery according to its own individual needs."
Therefore the batteries in this scenario don't need to be of the same type.
I run an ordinary wet cell starting battery and an AGM secondary battery. Both are controlled by a Piranha DBE150S "diode type" electronic isolator.
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99381
Follow Up By: Member - David C (QLD) - Wednesday, Feb 23, 2005 at 21:48
Wednesday, Feb 23, 2005 at 21:48
Hi Sandman,
I have a DBE150S isolator as
well and it isn't a diode type at all. If you open it up there are relays which do the switching and circuitry for delays, spike protection and current limiting. When the engine is on it parallels the batteries - when off it isolates them. I even measured the voltage in verses out and it is within 0.02 of a volt. If it had diodes then there would be at leset a 0.6 volt drop. A quick search revealed that there are electronic isolators, diode pack isolators and relay isolators around. The diode type are not really used anymore as it introduces a 0.6 volt voltage drop between batteries which means an insufficient charge to one of them. The common fix for this is that the regulator needs to be increased by 0.6 volt to counteract the effect of the diode but then another diode has to be put inline with the starter battery to make the circuit balanced. This isolation works
well on solar regulators where the output can be varied but is not practical for an alternator.
With regards to my problem, I think brett has the right answer in that AGM batteries do not like to be sitting at 14.4 volts forlong periods of time as they are designed to charge at a slightly lower voltage that lead acid batteries.
Please don't think I am saying anyones setup is wrong or won't work but
mine obviously didn't and at the cost of AGM batteries nowadays, it may pay to be mindful.
Regards
David
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Follow Up By: Mad Dog (Victoria) - Wednesday, Feb 23, 2005 at 22:14
Wednesday, Feb 23, 2005 at 22:14
I'm having a few problems coming to grips with this guys. If the batteries are simply paralled by this isolator then how can it treat each battery individually as quoted above from the Piranha website.
Quote: "The alternator is able to recharge each battery according to its own individual needs." Now that's got me stumped.
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Follow Up By: brett - Wednesday, Feb 23, 2005 at 23:03
Wednesday, Feb 23, 2005 at 23:03
That's the million dollar question, I've always suspected that there was not much electronic about the Piranha isolators and David confirms this. They still use relays for the switching like any other isolator, the only electronic bits are for current overload protection and the cut in/out voltages, just the same as most isolators on the market.
Re Piranha's quote it may be misleading but not incorrect, any two battery's in parallel will charge according to their own needs as their own internal resistance governs the charge current, but once fully charged it's a different story, your now talking float voltages which vary depending on type of battery. The only way to do this properly is to virtually build a switchmode inteliigent programmable battery charger and power it off 12V. Far too complicated and expensive for what we're doing.
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Follow Up By: Member - David C (QLD) - Wednesday, Feb 23, 2005 at 23:22
Wednesday, Feb 23, 2005 at 23:22
I think your on the money. However when you put 2 batteries of different states of charge together in a circuit they will equalise very quickly to assume almost identical voltage and capacities.
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Follow Up By: Member - Sand Man (SA) - Thursday, Feb 24, 2005 at 21:00
Thursday, Feb 24, 2005 at 21:00
David,
Yep, you are correct in that the DBE150S is not a "diode" type isolator.
It is an "electronic" isolator providing additional features.
However mate, I don't believe you are correct in your statement:-
"When the engine is on it parallels the batteries - when off it isolates them."
My understanding is that both batteries remain electrically isolated from each other, at all times.
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358201
Follow Up By: Member - David C (QLD) - Thursday, Feb 24, 2005 at 22:57
Thursday, Feb 24, 2005 at 22:57
Hi Sandman,
A quick
test will reveal they aren't. Disconnect the main and aux leads, connect 12 volts to the ignition on of the isolator, wait for approx 45 seconds for it to activate the isolator (in built delay to prevent large transition of current from one battery to the other when they are at different states of charge) and then measure the resistance from main lead to aux lead. You will find it is basically a short circuit. This prooves that it is purely a switch isolator (or relay).
You can also
test whilst connected. With engine running,
check voltage at main battery and voltage at aux battery, if within 0.1 volt (voltage drop of the isolator cable and relay) then they are paralled (best to do when battery voltage has stabilised as when you first start the engine the battery voltage increases slowly so reading a voltage of one battery and then the other will reveal that the volatge has increased a bit due to state of charge rising). Rev the engine and the voltage at the main battery will be exactly the same as the aux. That means there is absolutely no isolation when the isolator is activated.
There are isolators which do a different job and they have the alternator connected directly to the isolator and then the isolator switches in either battery to be charged depending on its voltage. This is a true isolator and I think the Rotronics falls under this catagory (anyone?).
Regards
David
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Follow Up By: Member - Sand Man (SA) - Friday, Feb 25, 2005 at 20:55
Friday, Feb 25, 2005 at 20:55
David,
I believe your testing procedure is faulty.
Some time ago I completely discharged a deep cycle wet cell battery.
There was NO impact to the primary (starting) battery at all.
That's the whole idea of having an isolator in the first place. (whatever the type, or brand)
If what you are saying was correct and the two batteries were connected in parallel, BOTH batteries would discharge, as they would be electrically (physically) connected together.
I will restate my comment that both batteries are electrically isolated from each other. You could run a winch, etc. off the primary battery until it is absolutely flat as a lizard drinking and guess what? The secondary battery will have as near a full charge as before the primary was drained, to the extent that one can physically jump start the vehicle using the secondary battery by PARALLELING it with the primary, or, if the primary was completely buggered, by replacing it with the secondary one altogether.
Cheers.
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