The post explores an innovative automatic dual battery charger with isolator circuit for alternators and engines, which allows monitoring of the charge levels of two individual batteries, and switching them across the loads appropriately. The idea was requested by Mr. Daz.
The Circuit Request
Very promising circuits you've always shared, actually I always visit your blog coz im also electronics hobbyist from Philippines ..
i have read many of your posted electronics design especially on battery charging circuits 🙂 its very simple and yet reliable and efficient circuits, building those circuits using your designs works great and thank you so much swagatam!
but until, i was thinking an solid-state automatic dual battery charger isolator for deep cycle agm 100ah batteries, i am using some of your design charging circuits and delay and relay techniques, but unfortunately, always got me an error...
what should I do sir?. can you guide me with my issues? thanks so much.
here is the step of how the circuit may do...
1. before starting, the two agm batteries 1&2 will combine in parallel connections to be used for starting the engine in order to provide smoother and more power to the start.
2.Then, once the engine is started, the battery 1 will automatically disconnect via a relay for automatic fast charging until float mode is reached.
3.while the battery 2 is connected, a voltage low level cut-off circuit will be monitoring its condition until its voltage reaches 11.5v,4.
When the low volt reaches 11.5v, the circuit will automatically trigger the relay connecting the fully charged battery 1 parallel with battery2.5.
after battery 1 is connected in parallel, a delay relay cut-off will disconnect of battery 2 and engage it for automatic fast charging and to float mode.6.a continuation cycle of relays, monitor, charging. that's it.
I hope you understand of what i mean.
hoping to hear from your sir. i hope you can help me with this circuits to make.
Thank you so much and more power to you sir!
The Circuit Design
Instead of addressing the two batteries as battery#1 and battery#2, I thought it was better identifying them as "charged battery", and "partially charged battery".
The proposed design of an automatic dual battery charger with isolator circuit for alternators may be understood with the following given points:
Initially due to absence of power, the two relays are held at their respective N/C positions which allow the two batteries to get connected in parallel with the load.
How the Batteries are Charged
Let's assume battery#1 as the charged battery, now when the engine is switched ON, both batteries provide their combined power to the alternator via the relevant N/C contacts.
As soon as the alternator starts, it powers the opamp circuit so that the opamps 1 and 2 which are configured as voltage comparators are able to sense the connected battery voltages at their relevant inputs.
As assumed above, since batt#1 has the higher voltage level, triggers opamp1 output high.
This in turn activates T1 and it's relay, which instantly disconnects battery#2 from the load.
Battery#2 now gets connected with the charger via the N/O contacts and starts getting charged at the relevant current.
At this point T1 executes two actions: It clamps the inverting input of opamp1 and non-inverting input of opamp2 to ground, latching their positions. It means the relays now hold their positions without any further interventions from opamp1 and 2.
In course of time, battery#1 starts getting discharged via the connected loads, and this condition is monitored by opamp3. The moment battery#1 charge reaches around 11.5V set by P2, opamp3 output goes low.
Since opamp3 output is connected to the base of T1, the above triggering instantly breaks T1 conduction resetting opamp1 and 2 into its original situation allowing them to yet again track the battery voltages.
This time battery2 being the one having higher potential activates opamp2/T2 and the lower relay.
The actions quickly disconnects battery1 from the load and connects battery#2 with the load.
Opamp4 now monitors battery#2 condition until its voltage also falls below the 11.5V mark when the situations yet again reverts.
The cycle continues as long as the engine and the load remain in the discussed chain.
The capacitors C1, C2 ensure a smooth transition between the relay switching.
As we can see in the above automatic dual battery charger with isolator circuit, the relay N/O contacts are responsible for the required charging of the connected relevant batteries.
Since these batteries need to be charged with an "intelligent" charger, the system should be a step-charger kind of unit.
One such circuit has been discussed in this 3 step battery charger circuit, which may effectively employed here for the proposed method of charging both the batteries.
All resistors are 1/4 watt CFR
R1, R2, R7, R8 = 10k
R3, R4, R5, R6 = 1M
P1, P2 = 10k presets.
D1, D2 = asper load current.
D3---D8 = 1N4007
All zener diodes = 4.7V, 1/2 watt
T1, T2 = 8050
C1, C2 = 220uF/50V
Relays = SPDT, 12V, 30 amps contacts
Opamps = LM324
Note: Connect the emitters of T1/T2 to ground through 1N4148 diodes, this is important otherwise the opamp3/4 outputs won't be able to switch OFF the BJTs correctly.