FET based 12v Battery Isolation circuit

Thread Starter

BurnedFingers

Joined Jun 29, 2010
6
The LiPo4 pack is 4 x 150ah that can be charged at about 0.2c so thats 120 amps there
The starter battery is lead acid 90ah and the anchor winch battery is 120ah lead acid
The alternator is a big body capable of sustained current draw for hours, Its from a combine harvester and driven with a serpentine belt. The idea is to quickly bulk up the lipos on rainy winter days before the solar charging takes over to complete the charge with a charge controller. The Lipos are then disconnected from the alternator charging with a battery switch leaving the starter battery

I figure a 200amp fet should be enough and maximum voltage of 15 or 16v depending on how I configure the alternator regulator


I do not need to make a charge controller, just simply a low voltage drop isolator (not zener diodes)
 

LowQCab

Joined Nov 6, 2012
3,929
What is the maximum Current-Output rating of the
Alternator at the specific RPM that it will be expected to be operating at ?

Will the Engine RPM vary ?, or is the Engine-RPM fixed by a Governor ?

What is the Pulley-Ratio between the Engine-Crankshaft and the Alternator ?

How much Current is normally required to operate all
of the other attached accessories on the Machine ?
Will those accessories be in use during external Battery-Charging activities ?

Does the Alternator have an external Voltage-Detection-Wire ?
If this Voltage-Detection-Wire is attached AFTER any Battery-Isolating-Diodes
the Charging-Voltage will remain correct, with a small loss in Maximum-Current-Output.

Will the auxiliary-Batteries remain connected for extended periods with the Machine not running ?
If they will NOT remain connected then no isolation is needed or wanted,
unless the Charging-Rate must be Regulated.

But You stated that You do not want a "Charge-Controller" ( Current-Regulator ) ........ Why ?
It sounds like a Current-Regulator, for each External-Battery, is exactly what You need.

0.2C sounds awfully low at first glance, but it will probably extend the Life-Expectancy of the Batteries.
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Thread Starter

BurnedFingers

Joined Jun 29, 2010
6
What is the maximum Current-Output rating of the
Alternator at the specific RPM that it will be expected to be operating at ?

Will the Engine RPM vary ?, or is the Engine-RPM fixed by a Governor ?

What is the Pulley-Ratio between the Engine-Crankshaft and the Alternator ?

How much Current is normally required to operate all
of the other attached accessories on the Machine ?
Will those accessories be in use during external Battery-Charging activities ?

Does the Alternator have an external Voltage-Detection-Wire ?
If this Voltage-Detection-Wire is attached AFTER any Battery-Isolating-Diodes
the Charging-Voltage will remain correct, with a small loss in Maximum-Current-Output.

Will the auxiliary-Batteries remain connected for extended periods with the Machine not running ?
If they will NOT remain connected then no isolation is needed or wanted,
unless the Charging-Rate must be Regulated.

But You stated that You do not want a "Charge-Controller" ( Current-Regulator ) ........ Why ?
It sounds like a Current-Regulator, for each External-Battery, is exactly what You need.

0.2C sounds awfully low at first glance, but it will probably extend the Life-Expectancy of the Batteries.
.
.
.
Max Current is 160 amps. The engine will operate at different rpms but im not sure how that is relevant?

The voltage regulator is internal and no sensing available

I am just looking for a very simple device.
I dont want to be rude but please accept that the rest of the system has been very thoroughly discussed, VERY
I am trying to avoid going down the rabbit holes of battery chenistry, voltage regulation etc etc etc

All I want to do is build a cheap FET based battery isolator capable of 200 amps at 15v
Thats it
PLEASE )
 

LowQCab

Joined Nov 6, 2012
3,929
"" The engine will operate at different rpms but im not sure how that is relevant? ""

You need to know all of the capabilities of your Alternator.
It will NOT provide 160-Amps at idle-speeds, while still maintaining around ~14.2 Volts.

Maximum-Output will probably be achieved over or around ~6000-RPM Alternator-Shaft-Speed.
Alternators designed specifically for use with Diesel-Engines may peak at lower speeds.

"" All I want to do is build a cheap FET based battery isolator capable of 200 amps at 15v ""

There is no such thing as Cheap+200-Amps.

What is the maximum permissible Charging-Current for a single externally connected Battery ?

Is less-than the maximum permissible Charging-Current ( more Charging-Time )
acceptable for each Battery ?

What is the lowest permissible Charging-Current ? ( longest Charging Time that is acceptable )

What does the Battery manufacturer state as the "Fully-Charged" Voltage-Level for the external Batteries ?

What is the exact Voltage that your Alternator produces with a normal light-Load at Idle-Speeds ?

There is no way to "side-step" or cheat doing the Math.

Going by your description of your external Batteries, especially the low Charge-Rate specified,
You will require some sort of Current and/or Voltage-Regulation for each Battery.

Unless You can tolerate some extended Charging-Times, ( maybe ~2X to ~4X longer ).

This does not have to be crazy expensive, but it is required,
unless You don't mind potentially destroying,
or seriously shortening the Life of,
some very expensive Batteries.

The Battery-Isolator that You linked to may damage your Batteries,
it is designed to work adequately with Automotive-Lead-Acid-Batteries only.
.
.
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Thread Starter

BurnedFingers

Joined Jun 29, 2010
6
[QUOTE

There is no way to "side-step" or cheat doing the Math.
.
[/QUOTE]

SIGH

I have tried to say this politely, but you are not hearing me

Thanks for the warnings, design education, opinions etc

THE DESIGN WORK HAS BEEN DONE
Please try to hear this

Its not a topic for discussion. I am not going to rehash it all here, There is a years worth of effort, testing, discussion pricing etc etc that has occurred in other groups with VERY qualified people

PLEASE TRY TO HEAR THIS



I came here to make one of these
https://www.amazon.co.uk/Victron-Energy-Argo-Battery-Isolators/dp/B078RD87KC

If you can point me to COMPONENTS and a CIRCUIT DESIGN that would be great

CAN YOU D HELP WITH THAT?

If yes great

If not, please let me be ok

Thanks
 

jiggermole

Joined Jul 29, 2016
161
Anything you spec out and design to replace the component you link to is going to be more expensive than the linked to component. You're stated goal of a cheap alternative is a foolish goal. There is no way you're going to out-cheap that chinesium device. Its just not going to happen. Cab's list is all the stuff you have to look at with component selection. All valid information for the task at hand.
 
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