Can the 12V battery work as power supply?

Hi everyone,

I’m currently working on a Twizy vehicle the urban-80 model of 2013-2012. The battery seems to discharge every now and then. This version has the old charger which only charges the 12V battery when connected to the wall or when switch is activated ( and not periodically even with ignition off as the new versions ).

I’ve read a lot of posts of people with the old charger having issues with their 12V battery. I’ve already changed the battery, without much improvement. The possibly aggravating cause, is that I have an external 150 to 300W load always connected in the 12V line. Does anyone know if the DC/DC converter is able to supply that kind of power and still be able to charge the auxiliar battery? My intuition tells me, I’m very steady but slowly dischargin the 12V battery. Has anyone test this kind of load with a twizy?.

I know it is a very technical issue, but if anyone can shed some light or recommendation it will be highly appreciated.

Why do you want to have a draw of between 12.5 and 25 amps? sounds a lot for such a small battery. No wonder it has gone flat. A new battery would only last an hour at the most. Have you considered a second battery in the boot. A matched pair of Lead Acid batteries in parallel is fine as long as the lead between the in thick enough.

Hey there thanks for the response, well I cannot really lower my power much more, nonetheless 300W should be unusual (peak). I figured since there is a DC/DC converter I’m not really pulling those amps from the auxiliary battery, but from the main battery (58V), that is IF the DC/DC (58V->12V) can supply that kind of power. It takes a month or so of light-use to discharge the auxiliary battery, which means I’m drawing some power (most of it actually) from the DC/DC. If the specs of the DC/DC converter were available I would be able to tell, if I’m discharging my batteries because of insufficient charge (more power amps draw from the 12V line than supply by the DC/DC) or is it just the problem everyone else is having but aggravated because of my load (old charger not being able to keep the auxiliary battery in good health).

A second battery could certainly work , but I think it would only solve the second hypothesis above, because if the DC/DC that charge the auxiliary battery/batteries cannot supply power to charge a battery and provide me the 150-300W, then a second battery won’t either, it would just take more time to discharge. Another possibility I’ve been thinking is to install a DC/DC converter from the 58V traction battery to 12V with enough power, this would probably solve issues regarding “drawing too much amps from the 12V”, but if the issue is in the charger, then I think the 12V auxiliary battery would eventually discharge, just slower.

For the charger see http://forum.evowners.com/t/12v-battery-purchase/1808/22

As it is a slow discharge stick a 40W solar panel to the Twizy roof and connect tot he 12V battery.

A solar panel would be a great solution, sadly it is not possible to fit one currently in the roof of the Twizy. I performed some tests with lighter loads, trying to find the sweet spot and found some enlightening results:

  1. With a continuous 80W load on the 12V, the 12V line starting to decline (signaling a drop in the battery charge). It declined 700mV (12.5 to 11.8 both measured under 80W load) in the course of 8-10 hours of continous load.

  2. Then the load was dropped to only 25W for around 8 hours. After doing so, I reapplied the 80W load, and found the 12V line increased to 12.4V (signaling that under 25W the batteries were “charging”).

This means I am very tightly close to the power the DC/DC can supply. Nonetheless I am not sure why… the DC/DC is 25Amps (300W) and my tests were performed well below that range. Which other electronics make use of the 12V?, the lights are off 99% of the time, I can only think of the ECU and the panel, but that cannot justify the over 200W in power that I seem to be missing.

Still I believed the most elegant (certainly not the cheapest) solution would be to install a DC/DC 400W directly from the 58V battery. What do you think?

I think there has been two different DC to DC charges used on the Twizy. One that is approx 17ah and one that is 25ah. I cannot tell you how to check or when the swap occurred. However it may explain your results. Also the DC/DC converter is no continuous in as much it only comes on every 20 mins of so. It might on the older Twiys not come at all unless the ignition is turned on.

80w of Solar panel is too big for the Twizy roof anyway and would assume you can park in the sun.