DC to DC chargers, do you really need one?

[native pepper]

Been using dc-dc chargers for years, got 3-4 on my bus and one on my car. One 24-12v feeds the gel batteries from a 60amp 24v battery, another feeds the 60amp 24v auxiliary battery from the starter batteries and another 12v-12v, feeds the 9amp battery running my new fuel pumps. My late mate put me onto it and it works really well, my lifepo4 pack runs on the roof panels on the bus, if I wanted to charge them from the bus, have another for that, it's 20 amp 12v-12v and can run through a 40amp dedicated lifepo4 charger. Never had to use it though as the lifepo4 never needs anymore than the panels. The gel are used as backup and for the hotwater heater, been to lazy to remove them after installing lifepo4 and they are still functioning properly.

[T1 Terry]

Ok, the charger should be mounted reasonably close to the hose battery to minimise voltage drop. I'm looking at getting DC to DC chargers made that have external voltage sensing, that would minimise that problem but for the moment, all DC to DC chargers I've tested so far sense their output voltage internally, so voltage drop after the charger would effect the voltage/current at the house battery.

Can the BMS system control the DC to DC charger, yes, it would require another SSR (solid state relay) and depending if the solar regulator is a Dingo or PL20 varies the control side wiring, but basically simple straight forward piggy back wiring to the other SSR's in the system.

OK, another bit that came to mind will driving 22hrs @ 90km/h, cause there is a lot of thinking time available Many DC to DC chargers offer a solar regulator function as well and label it an MPPT type controller. Technically they are not stretching the truth, they are a type of MPPT device, but they don't optimise the panel/s output, rather they suck in what ever they can get an pump it out at 14.4v. Some are limited to 16v max input and that is not suitable for most 12v panels as they have an open circuit output of 21v or more. Remember that once the battery is fully charged the DC to DC will stop sucking in the current from the panels and this is when the panel voltage will increase to as high as the open circuit voltage if there is no other path available.
Models such as the CTek D250s can handle both solar and alternator charging at the same time, but only to the 20 amps output limit, if the solar is not capable of supplying all the current required the efficiency is poor, but if there is enough solar to maintain the required current and better than 14v then they work great, the losses are due to the need for voltage boosting and this is not as efficient as voltage reducing, that is the reason most RV type MPPT controllers are voltage reducing only. In realty, if you have that much solar why waste it, fit a PWM controller and get the extra 20 amps from the DC to DC side when driving.

T1 Terry

[native pepper]

Yep, my chargers are situated right next to the batteries being charged, The run from the source on the pumps is about 2m and works excellently.

[bob r]

Terry have you had anything to do with one of these Ivertek dc/dc chargers.

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[Busman]

We run 1 of these for alt charging and another for load control on the eutectic fridge freezer, good pieces of gear

[T1 Terry]

Terry have you had anything to do with one of these Ivertek dc/dc chargers.
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These are solid state relay type DC to DC switches, they can not boost voltage or reduce voltage for 24 to 12v charging, they are a very sophisticated on/off switch but have voltage sensing and current sensing as well

[Busman]

Nope no current sensing, that was the next phase, never happened, then when Jaycar dropped them because of no one that could fix them that was the end of the range in Aussie. Have opened an account with them so I can import my own needs Rich stuff

[T1 Terry]

Nope no current sensing, that was the next phase, never happened, then when Jaycar dropped them because of no one that could fix them that was the end of the range in Aussie. Have opened an account with them so I can import my own needs Rich stuff

Ahhh.... another one of those write the product manual before the device is even made things eh, typical

[bob r]

OK will they work as a DC \ DC charge for lithium batteries?.

Bob

[Busman]

Yes but they will let everything through, they will do up to 100 amps, so your alt must be able to stand it, or you must use the cable as a limit for current.
They will stay connect till liths have reached programmed voltage then disconnect, this can kill some alts I believe. Ours is a huge coach alt, 270 amps at 24 v so it is fine, but smaller ones may die, there is no tapering effect with this device.