Wiring for LiFePO Battery

Farzad_k

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Hello.

The first thing I am doing to my new 6thGen Hybrid is to figure out wiring for my auxiliary battery that will be charged using the REDARC BCDC1225D charger. I will be drawing from the startup battery, but I am trying to figure out if I can place the additional 30 amp demand on the DC/DC charger that brings power to that end of the vehicle. The REDARC can produce only 25 amps but it can technically draw 35 amps to provide the 25 amps at 12 volts.

I don’t think this would be a problem. If anyone has already done something similar I appreciate any suggestions.

Farzad
 
I am interested in the answer as well. I am working on doing a similar thing. The difference is I have both a Victron 110V charger (30A @ 12V) and a 50A 12V DC to DC converter (programmatically set to 8A input so as not to overload the cigarette lighter) - as redundant approaches, in the hope one will work out. Note: Still building and testing it.
What I have read, is that if the lower spec Hybrid 4Runner (eg Off Road Hybrid) does not have the AUX switches installed from the factory, then it does not have the alternator installed (https://www.4runner6g.com/forum/thr...tor-to-the-iforce-max-hybrid.3853/#post-53338, https://www.4runner6g.com/forum/thr...-in-the-2025-gas-motor.5053/page-2#post-65125, https://www.4runner6g.com/forum/thr...r-output-and-dc-to-dc-system.4846/#post-62475). This means all power for 12V is coming from the Hybrid system - which may limit its current, at least for longer uses like charging. For higher power needs, you may want to add the alternator - it seems.
Note: in adding a brake controller, I have seen that the wiring harness is there for the Aux switches - needs the switches, fuses and relays - and now I understand also probably needs an alternator.
IMG_2064.jpeg
 
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What is a break controller and what does it have to do with an AUX switches?

What is an example of a higher power?
 
A brake controller is for a trailer. The vehicle I came with did not have a brake controller and it is recommended for light trailers and required for heavier trailers - so I need to install one. It controls the brakes on the trailer.
The brake controller was installed into the dash - behind where the AUX switches were. (https://6thgen4runner.com/threads/q...rket-trailer-brake-controllers.604/#post-2955). Hence I saw the wiring.
I do not know the answer to the higher power question. That is why I am also interested in anyone who does know. If the 12V power is getting converted down from the Hybrid system (at ~200V) then it is going to have a limit related to the DC-to-DC converter that does that job. For short bursts of power the 12V Lead Acid "starter battery" can provide the power - but for longer term draws it will fall back to the DC-to-DC connecting the Hybrid system to the 12V needs - I assume.
 
The comment in the link is about the built -in 2400 watt inverter not being able to deliver what it promises even at 1000 watts. That might very well be, and I imagine it is the limitation of the built-in inverter. The inverter may be situated downstream of the built-in DC-DC converter/charger and it is only one of the many circuits it supports. I am focusing on the starter battery and I think I am now seeing the picture.

Thinking out loud:

A “source” keeps the starter battery charged. The source pushes 14 volts into the starter battery when the engine is turned on (when the source is activated). The starter battery, with engine on or off, has four loads connected to it, and those can draw, based on fuse limitation, a maximum of 45 amps from the startup battery if they all came on at the same time. My REDARC, when added in, will be the 5th “load”, and it ants to draw 375 watts to be able to supply 375 watts of power to its load (my LiFePO). The REDARC draws from the startup battery only when it is at 14 volts, meaning it can add 27 amps to the 45 amps for a total demand of 72 amps if all five loads drew at the same time and at maximum fused power.

The question is then about the ability of the starter battery providing 72 amps. And it is clear to me now that the power delivery of the built-in DC-DC charger/converter does not come into picture at all in case of demands from the REDARC. The starter battery is a 70Ah battery.

I feel good about my discovery that I am only dealing with the starter battery and not what is upstream of it (the built-in DC-DC charger). Unless my LIFePO is depleted, the REDARC will not need to supply the maximum 25 amps, and therefore will not be drawing the maximum 27 amps. And I am sure the four circuits fused for 70 amps won’t be drawing that much ordinarily.

I will have to take some current measurements from the four loads I mentioned before. I can also upgrade the starter battery to something with higher capacity, something like a 100 Ah capacity if needed.









IMG_6697.jpeg
 
An interesting thread in another forum:

 
You can only cycle Lead acid batteries over 50% of their rated capacity, without dramatically shortening the battery life. Eg a 100Ah lead acid, you can only use 50Ah.
The Ah is a static charge holding capacity. It is not how much power it can supply at any point in time. Amps is the current being provided at any point in time - it is not the same as Ah the charge being stored.
A 100Ah battery can only give you 50Ah before it needs to be charged again (or a 25A current for 2 hours is another way of looking at it). If you are pulling charge out faster than you are replacing it, that is fine for a short while - but over a long time it creates a problem of taking more that the 50% limit (and ultimately more than a 100%, which is not possible) - whether this is a 100Ah or a 72Ah battery, the long term problem is the same - how much charge is coming in to replenish what you are taking out. It therefore is linked back to what the Hybrid system is able to give the 12V battery and other circuits through a DC to DC converter.
The link I put in my previous post (https://www.4runner6g.com/forum/thr...-2400w-power-output-and-dc-to-dc-system.4846/) talks about both 110V AC and 12V DC. It talks about the 12V DC decaying in current over time to about 9A.
Based on this, albeit 1 data point, if you want to continuously pull more than 8-9A from the 12V circuit, you probably need to add an alternator to give you that current, is my belief. But knowing more about what the Hybrid system can provide and the draws it has on it, would be more informative and definitive.
 

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