How to make a cheap isolated dual-battery setup for $50

carbon60

Explorer
yeah thats fine, however if your going to pull some serious amps through the chassis you should have redundant grounding paths for battery/engine (alt).. I once had engine ground strap fail and the path to ground for the starter was a throttle cable, bet yeh can guess how that turned out.

Great advice. I’ve got quite a lot in my 80, but I should replace a couple of them.

A.
 

Lucky j

Explorer
I do not want to interup a conversation here, and hope it will continue, but I just got a flash about the title of this tread.

Are we still in the 50,00$ original target or this tread, or did it turn out that is it not doable? That is in order to have something safe and reliable.

Thank you!
 

Krytos

Adventurer
Renogy has a new DC to DC charger unit on amazon for $129 if anyone is on the fence about solenoids and such. Has 3 stage charge and can handle flooded, agm, gel, and lithium. Output is 20 or 40 amps ($199) depending on model, but 20a is nice for those who don't wanna install huge wire (of course bigger is always better).

Renogy 20A DC to DC Battery Charger for Flooded, Gel, AGM, and Lithium Batteries Using Multi-stage Charging on Amazon

This is the solution I've been exploring as an alternative to the traditional solenoid system but during my research I found this charger which acts as a DC to DC charger with multiple charging profiles (LIFePo, Lead Acid, Gel, etc.) AND also has a built in MPPT solar charge controller and inputs for solar. It's a bit more expensive than the Renogy charger but the added utility of the MPPT charge controller is worth it in my opinion.
 

DorB

Adventurer
Yes.

I've always assumed that the frame is a zero resistance conductor when I use it for the negative return. What do others say?
The body is sitting on rubber bushings, and the original negative wire is not suited for heavy or distant installations.

I’ve added a second negative wire to the frame (10awg easier then replacing the original one).
And added a new negative wire from the frame to the trucks bed.
I can see the difference before and after.
 
This is the solution I've been exploring as an alternative to the traditional solenoid system but during my research I found this charger which acts as a DC to DC charger with multiple charging profiles (LIFePo, Lead Acid, Gel, etc.) AND also has a built in MPPT solar charge controller and inputs for solar. It's a bit more expensive than the Renogy charger but the added utility of the MPPT charge controller is worth it in my opinion.

CTEK also has something similar, with a built in MPPT controller as well. I'm using their 140amp system (the 250sa+smartpass), which I highly recommend (pricing is higher than renogy/your link/what I link below-but it also offers some other features). That's for a different thread however (haven't done a write up yet). The CTEK D250SA outputs up to 20amps, but the downside is that it does not have Lifepo4/lithium profiles. Price wise it's in between the Renogy and what you posted. $246 on amazon
 

john61ct

Adventurer
Apparently the Kisae charger will continue to draw off your starter battery regardless of charge source being active or not ?? !!

Sterling is my reco, fully adjustable user-custom setpoints.

Built-in solar controller fine for keeping batts topped up while not in use, otherwise get a better dedicated one like Victron.

But now thread drift is getting extreme

Sent from my Nexus 6 using Tapatalk
 

dwh

Tail-End Charlie
Apparently the Kisae charger will continue to draw off your starter battery regardless of charge source being active or not ?? !!

Do you mean for powering the on-board electronics, or charging? As to the first, the manual says it'll run from the house battery. As to the second, it has voltage sensing. It will fire up to put a load on the engine battery input and if the voltage is too low, it won't draw from that until the voltage rises over 13.2v.
 

dwh

Tail-End Charlie
Dunno. Didn't bother to study the whole manual. I just didn't buy the idea that a modern B2B would just keep going till it drained the engine battery. And it won't.
 

carbon60

Explorer
The body is sitting on rubber bushings, and the original negative wire is not suited for heavy or distant installations.

That makes sense. Though the original negative wire is quite short, so the resistance should still be minimal. I do think I'll redo that, however.

A.
 

john61ct

Adventurer
Dunno. Didn't bother to study the whole manual. I just didn't buy the idea that a modern B2B would just keep going till it drained the engine battery. And it won't.
Sure it will in this case, unless you set it not too. That's my point about that particular unit.

The 10.5v shutdown in that mode means zero SoC for a lead source battery, and IMO would be quite destructive for LFP.
 

john61ct

Adventurer
Adjustable setpoints are a big point in its favour, may pick one up for testing.

The LVD cutoff could always be controlled by an external relay / BMS.
 

dwh

Tail-End Charlie
Note A: When the battery is charging through CH3 with normal operation (not through Ignition or override setting), the charger will charge for 3 minutes, it will then rest for 5 seconds to verify the Input voltage. During the 5 seconds rest period, if the measured voltage is > Normal Under Voltage Recovery Voltage (> 12.8Vdc on a 12V system or > 25.6Vdc on a 24V system), the unit will continue the charging cycle through CH3. If the measured voltage on CH3 is < Normal Under Voltage Recovery Voltage (< 12.8Vdc on a 12V system or < 25.6Vdc on a 24V system), the unit will switch back to charge from CH2 (PV) until CH3 returns to Normal Start-Up Voltage (13.2V on a 12V System and 26.4V on a 24V system).

Also, during the 3 minutes charging process, if the measured terminal voltage drops below the Under Voltage de-rate voltage (11.5V for a 12V system, 23V for a 24V system), the charger will start to de-rated the output current. This function is used to compensate for the use of long or thin wire between the Input Battery System and the unit terminals. If the input voltage continues to drop below the Under-Voltage Shutdown Voltage (10.5V for a 12V system and 21V for a 24V system), the charging process will terminate and the unit will switch back to charge from CH2 (PV). It will only switch back to CH3 if the CH3 voltage returns to 13.2V on a 12V system or 26.4V on a 24V system



Voltage on alternator input has to be greater than 12.8v. Less than that and it switches to solar and doesn't switch back until alternator input exceeds 13.2v.
 

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