I have to start putting some thought into our vehicles battery system. Its installed into a Mazda BT50, and I did it this way because I didn't want to interfere with the vehicle computer, and charging system when fitting extra electrics.
The system has an auxiliary battery which is charged via a DC-DC charger. All of the added electrics come off the aux battery, including trailer lights, radios etc, etc. The caravan fridge (12v only) also runs off this battery when traveling, and can fed the caravan 12v system when power is low in the van as an emergency connection.
The trailer lights all go through a series of control relays, fitted by the tow bar supplier.
I have been told by various electrical experts that is a good way to wire the system, and ensures that the chance of a flat vehicle battery is minimized, avoiding any vehicle computer problems caused by trailer lights etc.
I have not seen any other RV vehicles wired up this way, and am now wondering because the life of the aux battery (80AH) is coming to an end, and I need to reduce the weight of the rig, should I
1/ stay with this system and replace the battery with a lithium, perhaps with reduced AH's.
Or 2/ remove the system altogether, and take all the power needed by outside sources from the main vehicle battery.
I would go with a lithium battery that fits in the same spot. No real value in going smaller capacity, the battery will be at least half the weight on the one you take out but quite likely twice the capacity. As it will be a single stand alone battery, not paralleled to another battery, and there are no big loads like an inverter, a drop in will do the job fine. No dea what cycle life you will get from a drop in and I can't really say whether a higher price drop in will give better value or a longer cycle life, they just haven't been around long enough to know. We know our battery will last longer than 10 yrs because we now have some that are 9yrs old and still performing as well as the day they were fitted and load test at better than 100% capacity still available.
T1 Terry
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Alan, that's right, its using a "Intervolt" charger, and I think the program suits lithium charging. But I don't see the harm using two different types of batteries, as they are electrically separated.
Alan, that's right, its using a "Intervolt" charger, and I think the program suits lithium charging. But I don't see the harm using two different types of batteries, as they are electrically separated.
I spoke to a Intervolt techo person a while back..... I have an Intervolt dc2dc and wanted yo use it with a lithium. They would not recomend it but mentioned that some customers have used them on the "AGM" profile. I hooked up a Winston 90ah battery and gave it a go.. as a aux under the bonnet of my LC200.
My findings were.... the AGM profile seems to work ok to charge (6 months so far) .... I have the display in cab so I can see whats going on........ BUT/HOWEVER... once in float.... at 13.2v... non adjustable.... the charger does not seem to contribute to any load on the battery.... as battery supplies load because it is at a higher voltage.... and the big BUT.... the Intervolt will not go from float to bulk again until it "sees" about 12v (it stops charging every now and again to check battery voltage)..... so doesn't sense a slightly discharged lithium (say 13v).
I have got around these issues and can provide detail if interested.
-- Edited by Noelpolar on Thursday 12th of September 2019 08:04:55 PM
Hi Alan, no the aux battery is charged via the DCDC charger, on that they are electrically separated. As for changing the aux to lithium, that's down the track. At the moment I am only applying thought to the fact that the aux supplies everything, including caravan brakes, stop and indicator lights. It is wired up using all the correct circuit breakers and fuses. However the battery is nearing the end of its life, and as it is a vital part of the set up, I have to start thinking of replacement, or re wire the system, and do away with the auxiliary all together.
So far the system has worked flawlessly, and there is no danger of upsetting the vehicle computer no matter what Trailer I tow. In order to cut down on weight I see I have two options here, replace the battery with a lithium, or do away with the aux altogether. The latter will require major rewiring, and also leaves us vulnerable to having a flat battery, however as I understand it most vehicles are wired this way, I have jump started a few : ).
So I am merely throwing some thoughts around my head at this stage. Of course if I take the battery in to be tested, they will deem it U/s, why would they say otherwise, so its just a case of making the plunge when ready.
I have four 26ah batteries charged via Victron DC to DC charger up to 18amps, for 28L fridge & charging phone, camera & torches. Fridge uses about 12 to 15ah per 24 hours.
Have you looked very seriously at other items that you really do not need or replace with lighter alternatives rather than shrinking the battery.
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As I said, easiest and best option is swap out the existing Aux battery for a lithium battery the same physical size. The DC to DC dropping into a float mode of 13.2v is rather annoying, is it were 13.8v that would be find but 13.2v for a lithium battery is close to fully discharged. Maybe Intervolt has a fix for this problem, worth contacting them and asking, or try Noelpolar's idea for a work around. I advise against putting a lithium battery or even an AGM battery under the bonnet where the heat is above 60*C as it will cause an early death to both types of battery. Under bonnet is the realm of flooded cell batteries that you can top up with water when it boils out. If you build a good heat shield and can force cool the battery enclosure with fresh cool air from the grill then under the bonnet is fine.
T1 Terry
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Iana I would suspect that the two batteries are paralled internally when they are charging. I can see two problems with this.
1 The battery with lower internal resistance (lithium) would accept the bulk of the out put until it reaches 14.2 V when the charger switches to float 13.2 V leaving the agm battery with little charge
2 If the Aux battery is also an agm, if it is not similar in capacity to the house battery the smaller may reach the float switch point voltage before the larger is adequately charged. Probably less of a problem than different chemistry.
Oh Sh!t, I see where the thinking has gone wrong, my discussion is about the vehicle start battery and the aux battery fitted to the vehicle, the van batteries are charged via solar, and when traveling are isolated from the vehicle supply, This supply powers the 12v fridge, or any other 12v requirement in the van, when the vehicle is connected. I shall have another read of the manual just to check that. But yes Lithium batteries for the van will be on the list, pity we have just replaced the original's with AGM, but I have also fitted a MPPT controller that's lithium compliant, but that is an issue for the future.
Quote from the manual "Auxiliary Power Input: The power supply terminal Aux In +VE provides an alternative option for powering of the load and float charging of the batteries when mains voltages are not present. This input is to be powered by a suitable +12V system. (i.e. CAR). The voltage of the auxiliary power source should not exceed 14.8 volts." So the aux battery would be providing a "Float" charge only I assume.
-- Edited by iana on Saturday 14th of September 2019 09:34:58 AM
If your happy with the current setup and it does what you want just replace it with another agm as the weight saving is bugger all in the big scheme of things
Otherwise you'll have to set it up differently to suit whichever way you go costing a fair bit of money , though that's up to you , just my observation to your situation
