Thread: Beware Charging Dual Battery in D4.

Hi Drivesafe,

Not sure that I understand your post. I have 1 standard battery and 2x60AH 2nd/3rd batteries. I am charging the two extra batteries in about 4 hours driving but I cant tell you from what state of charge. All I know is that I am not concerned about the time it takes to charge them... although 10 minutes would be nice

Peter

ahhh and a couple of questions Drivesafe....

What would the rate of charge into the secondary batteries be when they are directly connected to the car charging system as they would be with the Traxide?

Also do you know what the maximum charge rate is that most batteries can take?

What happens when the main battery is say at 80% SoC and the secondaries are at 50% SoC and the car is then started. How does the Traxide system now correctly charge batteries that are different SoC?

Peter

comes down to the types of batteries.

good wet cells that arent below say 50% soc will take a 100Amp charge rate if you need them to but you dont want to try to push that into them once they hit about the 80% charge point..

in super simple terms and without involving the complexities of line drop, temperature, age, damage or charging with a load applied.

if you have all your batteries hooked up in parallel then the ones that have the lowest SOC will draw down on all the other batteries until the batteries all reach about the same SOC

when parallel charging the batteries that need the most current to charge take the lions share of the current until everything's equal and then the rate evens out.

Hi again Peter, first off, from the info you posted, it’s just some basic math that gives a VERY rough idea of how low your two 60 AH batteries were when you started your drive.

On average, if you have taken 4 hours to fully charge the 120 Ah capacity you have, working backwards, ( it will make sense soon ) as it would take your DC-DC device about 90 to 120 minutes to get your batteries from around 80% to 100% SoC. Remember Dc-Dc devices do not charge the last 15-20% of the battery’s capacity at 20 amps, it tapers off as the battery reaches the last stages of it’s charge.

So this leaves 120 to 150 minutes to get the batteries up to around 80% ( about 96 Ah ), which means at 20 amps an hour, you have put 40 to 50 amperes back into you batteries, which in turn means your batteries were not likely to be any lower than about 45% SoC. This equates to about 75 Ah used.

This means if you had an SC80 system, and used the same amount of power, your cranking battery ( a 110 Ah battery ) and you two 60 Ah auxiliary batteries will only be discharged down to about 67% SoC EACH.

So it will take your alternator a lot less time to being all the batteries simultaneously back from 66% SoC to say 95% than is takes your DC-DC device to get your two 60 Ah batteries from 45% to 95%.

As to maximum charge rates, most Standby type AGMs take full inrush currents but this full inrush current can damage them if it’s too high and Standby type AGMs are actually current limited to somewhere between 20% to 35% of the total capacity. For example, a give brand of 100 Ah AGM might have a charge/discharge maximum rate of 25%, so the 100 Ah battery will only tolerate up to 25 amps of charge current.

You need to check the specs for each specific brand and model of Standby type AGM to get the exact charge/discharge maximum rate for that battery.

Flooded wet cell batteries are literally self-regulating and this means you can apply any amount of charge current you want but these types of batteries will only take what the want. This includes Ca/Ca batteries.

Last but not least, if you have one of my SC80 systems fitted then the cranking battery and the auxiliary battery would both be at 75% SoC not 80% and 50%.

Because you are on a great battery explanation, let me ask a couple of added questions.

Why do folks use a "yellow top" battery as a second battery with 2nd battery charging systems, versus an adding a second identical battery as OEM (in my case an MTP-H8 Interstate).

On my boat, the solution to getting a longer cycle use for the 12v systems was to install 2 6volt golf cart batteries, cross them over to make 12v. The battery seeming gives a longer, deeper cycle extending the length of time needed between charges. Would this be an option for some people with trailers, etc. that want more time, and have room for added batteries.

Hi Unseenone, in most cases where the D3 and D4 are concerned, the Optima D34, 55 Ah battery is a perfect fit and while there are other batteries that come close, they usually need some form of modification to be done to get them to fit.

The D34 just drops straight in.

There is a nice advantage to using the D34 in a D3 or D4. The yellow top charges at a much faster rate than most other batteries so in situations where people regularly don’t drive long enough after starting the motor, to fully charge the cranking battery, the Optima in conjunction with the way the SC80 isolator works, means the cranking battery can get a bit of a topping up from the Optima.

This helps to extend the operating life of the cranking battery that would normally, in these situations, end up going flat regularly and having a short life span.

I have had quite a few customers, who were getting low battery messages prier to fitting an SC80 DBS, but once the system was fitted, they never got the message again.

Note, this was not a planned design feature in the way the SC80 works, it just turns out to be an additional benefit to the other features of the way the SC80 works.

Duplicate message, but could not figure out how to delete it.

Originally Posted by unseenone

Because you are on a great battery explanation, let me ask a couple of added questions. Why do folks use a "yellow top" battery as a second battery with 2nd battery charging systems, versus an adding a second identical battery as OEM (in my case an MTP-H8 Interstate). .

The link below is to my Gallery on disco3 where I show off my Traxide dual battery install on my LR3. The battery I used is a CaCa type that looks and acts just like the Interstate H8.

I did try to purchase an exact Interstate H8, but could not get a similar sized one to fit in the driver's side location due to the brake reservoir taking up a bit more space than desirable and also my unwillingness to trim off some plastic angle reinforcing in the lower front of the second battery box area. If I had have trimmed the plastic, I think an Interstate H6 would have fit as it is shorter in length.

My dual battery link section has a number of pdf files of locally available USA sized batteries. The battery I did install was a Made in USA Deka brand; the main reason for the CaCa type was I wanted a shallow cycle battery for engine starting purposes in cold weather, not a deep cycle for running fridges and the like.

DISCO3.CO.UK Photo Gallery - Traxide Dual Battery install in LHDrive