Multistage charging over different battery chemistries. Integrated solar input and regulation. Potential for improved monitoring.

The alternator alone doesn't fully charge your batteries by a good margin, so you're not getting the capacity you paid for and their life is shortened.

Smart alternator

denmonkey wrote:

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then yu can tell everyone you have one :)

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and the winner is ....... :lol:

 

T1 Terry 

Sarge9 wrote:

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And in any case my prefered supplier of things battery and solar..... Blue Apple Solar.... said no, don't waste ya money. When I explained what i was doing, what i had read . They were not going to sell me one.

Good luck.
Sarge.

-- Edited by Sarge9 on Tuesday 29th of October 2019 09:43:51 PM

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 Wow...good to see some companies still have high standards and don't just chase the $s.

Sarge9 wrote:

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It seem to be a relevant question. And bragging rights seem to be the common answer.
I have no expertise. But with my Colorado putting out 14.2 fairly constantly and down to 13.0 as day wears on, I can't see how a DC to DC charger could improve on that. If the tug has an older style simple Alternator with a flat 13 or less out put then may be the DC to DC can do some magic. Or am I just piddling in the wind again. And in any case my prefered supplier of things battery and solar..... Blue Apple Solar.... said no, don't waste ya money. When I explained what i was doing, what i had read . They were not going to sell me one.

Good luck.
Sarge.

-- Edited by Sarge9 on Tuesday 29th of October 2019 09:43:51 PM

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How about I try the maths approach to assist in deciding if a DC to DC charger could be an advantage or just a $$ grabbing gimmick.

First we will use the 14.2v start battery charging as can be found in the early non computer controlled everything vehicles. A basic alternator with either an internal or external regulator.

 

Basic model, start battery and alternator are at the front of the tow vehicle. A cable is run from the start battery to a fuse and then on to the towbar and an Anderson plug, we will ignore the VSR or solenoid for this simplified example, don't do this in your install unless you are willing to unplug the Anderson plug each time you stop to avoid draining the start battery.

Next we have the draw bar on the caravan with the Anderson plug and cable that runs back to the house battery. We will add a fuse in here as well because we would be messing with a disaster with the house battery being the power source for a short any where along the cable back to the start battery fuse. At 14.2v from the start battery we could use 6 B&S cable (13.5mm sq) as this is rated to a safe maximum of 125 amps, we will fit a 100 amp fuse at each end. For the sake of numbers, let's say the alternator can handle a continuous output of 140 amps, rare but it doesn't matter for this example.

Length of cable from the start battery to the towbar allowing for the extra bit to follow a safe path so the cable will avoid being damaged, 10 mtrs say.

Now the caravan draw bar to the house battery, mid mounted, 7 mtrs? Total 17 mtrs of cable, 2 fuses, 2 Anderson plugs and 8 crimp lugs on the positive cable ( battery terminal, fuse in, fuse out, Anderson plug, van Anderson plug, fuse in, fuse out, house battery.) and 4 on the negative, (start battery, Anderson plug, van Anderson plug, house battery) a total of 12 crimp joints. This is important to keep in mind because every joint adds resistance, very little for a really good joint but it can be a lot with a poor joint.

How much battery charging are we expecting, we have a 140 amp alternator after all, let's be gentle and aim for 40 amps the same as the bigger DC to DC chargers can deliver.

So the sum is, 40 amps @ 14.2v over 17 mtrs plus the joints, add what ever number of mtrs you think applicable but we will say every joint is perfect in our perfect world. Feed this into an on line calculator https://www.youtube.com/watch?v=Mvy3g_NIr8s&list=PL2l32K1w0jp-m04Jl-3PHmtapevOuCeIp&index=21&t=0s conductor is copper, cable AWG is 6 (B&S and AWG are close enough to the same for this example) 14vdc, DC voltage, 1 conductor pair,  17 mtrs cable length and 40 amps is what we want to come out the other end, press the magic button and it tells us that 14.2v at 40 amps in one end will come out as 12.4v at 40 amps at the other end.

12.4v will not fully recharge a battery that was only drained to 50% SOC, 12vdc At 50% SOC means there is only 0.4v difference between what is coming in and what is already there .... 40 amps will not flow into a lead acid battery with only a 0.4v difference. If you doubt that statement, try it with a set of jumper leads between a battery at 12.4v and a second battery at 12v, and this is only a few meters of cable.

To even achieve a float voltage at the house battery we have to reduce the current (amps) we expect to see travel through the cable

Back to the on line calculator and we can start reducing the amps till we see 13.8v come out the other end, at 8 amps we can get 13.85vdc out of the other end. 

If you have a 100Ah AGM battery discharged to 50% SOC, you need to put back more than the 50 amps you took out to cover the internal losses, being generous we will say 10% (really around 20%)  so we need 55 Ah and we have an 8 amp charger, it will take around 9 hrs driving if the battery would accept the full 8 amps right up to 100% SOC and there was nothing else running in the caravan, that includes the fridge.

Not going to happen is it .... do the sums  if you have a bigger battery bank, now add in a solar regulator as well, it will try to get the battery up to 14.4v before dropping back to the 13.8v float charge, as soon as the voltage reaches 14.1v in the house battery, less than 1 amp will flow down from the alternator .... all the charging will now be solar charging.

 

Add a DC to DC charger at the house battery end, we want 40 amps at 14.4v max ready to charge the house battery to get it recharged as quick as possible, 40 x 14.4v = 580w output, add 10% for the losses through the DC to DC charger and we now need around 650w.

Let's go back to the first run through the on line calculator, 40 amp @ 14.2v one end comes out as 40 amps @ 12.44v at the other end. 40 x 12.44v = roughly 500w, but we need 650w going into the DC to DC charger to get the 40 amps @ 14.4v out the other end .... more amps required.

55 amp x 11.78v =  647.9w, close enough for our 650w input requirement. (run the 55 amps through the on line calculator and 11.78v is the result)

 

This all hinges on there being a constant 14.2v at the start battery and there is zero resistance through all those crimp, bolted joints, fuses and Anderson plug connections.

 

A long read I know, but does it make any more sense now?

 

T1 Terry  

 

Thanks Terry. Vehicle charging is only one part of the system, we have solar and a 240v charger that puts out 40 amps to the batteries whilst the genset is running for microwave and/or coffee machine.

I will be watching things closely and with interest when we head to Portland on the 19th Nov. It will be the first time with all good batteries, solar, vehicle charging, and the 40 amp AC charger.

Aussie Paul. 

It's not clear how far it actually is from the DC-DC charger to the batteries.

Run the negative cables from the start battery to the DC to DC charger and from the DC to DC charger to the Anderson plug. On the caravan run the negative cable from the Anderson plug to the battery terminal. Using chassis earth links causes more grief in RV electrics than just about any other problem due to the poor contact that often occurs between the cable terminal and the metal chassis surface. These rust or oxidise quickly due to current passing through dissimilar metals and this creates voltage drop.
The cable from the DC to DC through to the house battery sound good enough to carry the current, split the power to the 3 way fridge away from the house battery cable at the Anderson plug but be sure to switch the fridge over to gas as soon as you stop, or better still, use a fridge switch that is virtually a motion sensor that will disconnect the battery power from the fridge 10 mins after you stop moving. I would recommend fitting one of these au.rs-online.com/web/p/rectifier-diodes-schottky-diodes/4859604/ on a heatsink close to the battery on that DC to DC cable to stop the 3 way fridge from trying to use the house battery to power it rather than from the DC to DC charger.
As far as the "Smart Pass" it will be interesting to see how that goes for you. The theory is good, but within 10 mins of the DC to DC running the smart pass doesn't seem to pass much current at all from the tests we have done. Might work better for deeply discharged lead acid batteries, we only work with lithium batteries so all the tests involved recharging lithium batteries and not lead acid batteries.
The only other thing, how much current will the 3 way fridge draw? Just wondering if there will be enough left from the 25 amps from the DC to DC to charge the battery.

T1 Terry

Hi Guys
Many thanks for the advice. This is exactly what I was looking for.
Noting that the -ve connection (Batt to DC/DC) should be cable rather than chassis conflicts with local "Battery expert" but I understand your reasoning, No probs with that as I have heaps of 25mm2 cable. Just passing two of them around bends will be diffficult.
I will check on the 3-way fridge consumption. I think I have a 15amp fuse in there but will check.
I looked at the Diode assembly but not really sure how it shold be connected. Maybe will go with the "fridge switch" as that seems more understandable.
Regards